exec.c

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/*
 *  linux/fs/exec.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

/*
 * #!-checking implemented by tytso.
 */
/*
 * Demand-loading implemented 01.12.91 - no need to read anything but
 * the header into memory. The inode of the executable is put into
 * "current->executable", and page faults do the actual loading. Clean.
 *
 * Once more I can proudly say that linux stood up to being changed: it
 * was less than 2 hours work to get demand-loading completely implemented.
 *
 * Demand loading changed July 1993 by Eric Youngdale.   Use mmap instead,
 * current->executable is only used by the procfs.  This allows a dispatch
 * table to check for several different types  of binary formats.  We keep
 * trying until we recognize the file or we run out of supported binary
 * formats. 
 */

#include <linux/slab.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/mm.h>
#include <linux/stat.h>
#include <linux/fcntl.h>
#include <linux/swap.h>
#include <linux/string.h>
#include <linux/init.h>
#include <linux/pagemap.h>
#include <linux/perf_event.h>
#include <linux/highmem.h>
#include <linux/spinlock.h>
#include <linux/key.h>
#include <linux/personality.h>
#include <linux/binfmts.h>
#include <linux/utsname.h>
#include <linux/pid_namespace.h>
#include <linux/module.h>
#include <linux/namei.h>
#include <linux/mount.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/tsacct_kern.h>
#include <linux/cn_proc.h>
#include <linux/audit.h>
#include <linux/tracehook.h>
#include <linux/kmod.h>
#include <linux/fsnotify.h>
#include <linux/fs_struct.h>
#include <linux/pipe_fs_i.h>
#include <linux/oom.h>
#include <linux/compat.h>

#include <asm/uaccess.h>
#include <asm/mmu_context.h>
#include <asm/tlb.h>

#include <trace/events/task.h>
#include "internal.h"
#include "coredump.h"

#include <trace/events/sched.h>

int suid_dumpable = 0;

static LIST_HEAD(formats);
static DEFINE_RWLOCK(binfmt_lock);

void __register_binfmt(struct linux_binfmt * fmt, int insert)
{
    BUG_ON(!fmt);
    write_lock(&binfmt_lock);
    insert ? list_add(&fmt->lh, &formats) :
         list_add_tail(&fmt->lh, &formats);
    write_unlock(&binfmt_lock);
}

EXPORT_SYMBOL(__register_binfmt);

void unregister_binfmt(struct linux_binfmt * fmt)
{
    write_lock(&binfmt_lock);
    list_del(&fmt->lh);
    write_unlock(&binfmt_lock);
}

EXPORT_SYMBOL(unregister_binfmt);

static inline void put_binfmt(struct linux_binfmt * fmt)
{
    module_put(fmt->module);
}

/*
 * Note that a shared library must be both readable and executable due to
 * security reasons.
 *
 * Also note that we take the address to load from from the file itself.
 */
SYSCALL_DEFINE1(uselib, const char __user *, library)
{
    struct file *file;
    struct filename *tmp = getname(library);
    int error = PTR_ERR(tmp);
    static const struct open_flags uselib_flags = {
        .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC,
        .acc_mode = MAY_READ | MAY_EXEC | MAY_OPEN,
        .intent = LOOKUP_OPEN
    };

    if (IS_ERR(tmp))
        goto out;

    file = do_filp_open(AT_FDCWD, tmp, &uselib_flags, LOOKUP_FOLLOW);
    putname(tmp);
    error = PTR_ERR(file);
    if (IS_ERR(file))
        goto out;

    error = -EINVAL;
    if (!S_ISREG(file->f_path.dentry->d_inode->i_mode))
        goto exit;

    error = -EACCES;
    if (file->f_path.mnt->mnt_flags & MNT_NOEXEC)
        goto exit;

    fsnotify_open(file);

    error = -ENOEXEC;
    if(file->f_op) {
        struct linux_binfmt * fmt;

        read_lock(&binfmt_lock);
        list_for_each_entry(fmt, &formats, lh) {
            if (!fmt->load_shlib)
                continue;
            if (!try_module_get(fmt->module))
                continue;
            read_unlock(&binfmt_lock);
            error = fmt->load_shlib(file);
            read_lock(&binfmt_lock);
            put_binfmt(fmt);
            if (error != -ENOEXEC)
                break;
        }
        read_unlock(&binfmt_lock);
    }
exit:
    fput(file);
out:
    return error;
}

#ifdef CONFIG_MMU
/*
 * The nascent bprm->mm is not visible until exec_mmap() but it can
 * use a lot of memory, account these pages in current->mm temporary
 * for oom_badness()->get_mm_rss(). Once exec succeeds or fails, we
 * change the counter back via acct_arg_size(0).
 */
static void acct_arg_size(struct linux_binprm *bprm, unsigned long pages)
{
    struct mm_struct *mm = current->mm;
    long diff = (long)(pages - bprm->vma_pages);

    if (!mm || !diff)
        return;

    bprm->vma_pages = pages;
    add_mm_counter(mm, MM_ANONPAGES, diff);
}

static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
        int write)
{
    struct page *page;
    int ret;

#ifdef CONFIG_STACK_GROWSUP
    if (write) {
        ret = expand_downwards(bprm->vma, pos);
        if (ret < 0)
            return NULL;
    }
#endif
    ret = get_user_pages(current, bprm->mm, pos,
            1, write, 1, &page, NULL);
    if (ret <= 0)
        return NULL;

    if (write) {
        unsigned long size = bprm->vma->vm_end - bprm->vma->vm_start;
        struct rlimit *rlim;

        acct_arg_size(bprm, size / PAGE_SIZE);

        /*
         * We've historically supported up to 32 pages (ARG_MAX)
         * of argument strings even with small stacks
         */
        if (size <= ARG_MAX)
            return page;

        /*
         * Limit to 1/4-th the stack size for the argv+env strings.
         * This ensures that:
         *  - the remaining binfmt code will not run out of stack space,
         *  - the program will have a reasonable amount of stack left
         *    to work from.
         */
        rlim = current->signal->rlim;
        if (size > ACCESS_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4) {
            put_page(page);
            return NULL;
        }
    }

    return page;
}

static void put_arg_page(struct page *page)
{
    put_page(page);
}

static void free_arg_page(struct linux_binprm *bprm, int i)
{
}

static void free_arg_pages(struct linux_binprm *bprm)
{
}

static void flush_arg_page(struct linux_binprm *bprm, unsigned long pos,
        struct page *page)
{
    flush_cache_page(bprm->vma, pos, page_to_pfn(page));
}

static int __bprm_mm_init(struct linux_binprm *bprm)
{
    int err;
    struct vm_area_struct *vma = NULL;
    struct mm_struct *mm = bprm->mm;

    bprm->vma = vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
    if (!vma)
        return -ENOMEM;

    down_write(&mm->mmap_sem);
    vma->vm_mm = mm;

    /*
     * Place the stack at the largest stack address the architecture
     * supports. Later, we'll move this to an appropriate place. We don't
     * use STACK_TOP because that can depend on attributes which aren't
     * configured yet.
     */
    BUILD_BUG_ON(VM_STACK_FLAGS & VM_STACK_INCOMPLETE_SETUP);
    vma->vm_end = STACK_TOP_MAX;
    vma->vm_start = vma->vm_end - PAGE_SIZE;
    vma->vm_flags = VM_STACK_FLAGS | VM_STACK_INCOMPLETE_SETUP;
    vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
    INIT_LIST_HEAD(&vma->anon_vma_chain);

    err = insert_vm_struct(mm, vma);
    if (err)
        goto err;

    mm->stack_vm = mm->total_vm = 1;
    up_write(&mm->mmap_sem);
    bprm->p = vma->vm_end - sizeof(void *);
    return 0;
err:
    up_write(&mm->mmap_sem);
    bprm->vma = NULL;
    kmem_cache_free(vm_area_cachep, vma);
    return err;
}

static bool valid_arg_len(struct linux_binprm *bprm, long len)
{
    return len <= MAX_ARG_STRLEN;
}

#else

static inline void acct_arg_size(struct linux_binprm *bprm, unsigned long pages)
{
}

static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
        int write)
{
    struct page *page;

    page = bprm->page[pos / PAGE_SIZE];
    if (!page && write) {
        page = alloc_page(GFP_HIGHUSER|__GFP_ZERO);
        if (!page)
            return NULL;
        bprm->page[pos / PAGE_SIZE] = page;
    }

    return page;
}

static void put_arg_page(struct page *page)
{
}

static void free_arg_page(struct linux_binprm *bprm, int i)
{
    if (bprm->page[i]) {
        __free_page(bprm->page[i]);
        bprm->page[i] = NULL;
    }
}

static void free_arg_pages(struct linux_binprm *bprm)
{
    int i;

    for (i = 0; i < MAX_ARG_PAGES; i++)
        free_arg_page(bprm, i);
}

static void flush_arg_page(struct linux_binprm *bprm, unsigned long pos,
        struct page *page)
{
}

static int __bprm_mm_init(struct linux_binprm *bprm)
{
    bprm->p = PAGE_SIZE * MAX_ARG_PAGES - sizeof(void *);
    return 0;
}

static bool valid_arg_len(struct linux_binprm *bprm, long len)
{
    return len <= bprm->p;
}

#endif /* CONFIG_MMU */

/*
 * Create a new mm_struct and populate it with a temporary stack
 * vm_area_struct.  We don't have enough context at this point to set the stack
 * flags, permissions, and offset, so we use temporary values.  We'll update
 * them later in setup_arg_pages().
 */
int bprm_mm_init(struct linux_binprm *bprm)
{
    int err;
    struct mm_struct *mm = NULL;

    bprm->mm = mm = mm_alloc();
    err = -ENOMEM;
    if (!mm)
        goto err;

    err = init_new_context(current, mm);
    if (err)
        goto err;

    err = __bprm_mm_init(bprm);
    if (err)
        goto err;

    return 0;

err:
    if (mm) {
        bprm->mm = NULL;
        mmdrop(mm);
    }

    return err;
}

struct user_arg_ptr {
#ifdef CONFIG_COMPAT
    bool is_compat;
#endif
    union {
        const char __user *const __user *native;
#ifdef CONFIG_COMPAT
        const compat_uptr_t __user *compat;
#endif
    } ptr;
};

static const char __user *get_user_arg_ptr(struct user_arg_ptr argv, int nr)
{
    const char __user *native;

#ifdef CONFIG_COMPAT
    if (unlikely(argv.is_compat)) {
        compat_uptr_t compat;

        if (get_user(compat, argv.ptr.compat + nr))
            return ERR_PTR(-EFAULT);

        return compat_ptr(compat);
    }
#endif

    if (get_user(native, argv.ptr.native + nr))
        return ERR_PTR(-EFAULT);

    return native;
}

/*
 * count() counts the number of strings in array ARGV.
 */
static int count(struct user_arg_ptr argv, int max)
{
    int i = 0;

    if (argv.ptr.native != NULL) {
        for (;;) {
            const char __user *p = get_user_arg_ptr(argv, i);

            if (!p)
                break;

            if (IS_ERR(p))
                return -EFAULT;

            if (i++ >= max)
                return -E2BIG;

            if (fatal_signal_pending(current))
                return -ERESTARTNOHAND;
            cond_resched();
        }
    }
    return i;
}

/*
 * 'copy_strings()' copies argument/environment strings from the old
 * processes's memory to the new process's stack.  The call to get_user_pages()
 * ensures the destination page is created and not swapped out.
 */
static int copy_strings(int argc, struct user_arg_ptr argv,
            struct linux_binprm *bprm)
{
    struct page *kmapped_page = NULL;
    char *kaddr = NULL;
    unsigned long kpos = 0;
    int ret;

    while (argc-- > 0) {
        const char __user *str;
        int len;
        unsigned long pos;

        ret = -EFAULT;
        str = get_user_arg_ptr(argv, argc);
        if (IS_ERR(str))
            goto out;

        len = strnlen_user(str, MAX_ARG_STRLEN);
        if (!len)
            goto out;

        ret = -E2BIG;
        if (!valid_arg_len(bprm, len))
            goto out;

        /* We're going to work our way backwords. */
        pos = bprm->p;
        str += len;
        bprm->p -= len;

        while (len > 0) {
            int offset, bytes_to_copy;

            if (fatal_signal_pending(current)) {
                ret = -ERESTARTNOHAND;
                goto out;
            }
            cond_resched();

            offset = pos % PAGE_SIZE;
            if (offset == 0)
                offset = PAGE_SIZE;

            bytes_to_copy = offset;
            if (bytes_to_copy > len)
                bytes_to_copy = len;

            offset -= bytes_to_copy;
            pos -= bytes_to_copy;
            str -= bytes_to_copy;
            len -= bytes_to_copy;

            if (!kmapped_page || kpos != (pos & PAGE_MASK)) {
                struct page *page;

                page = get_arg_page(bprm, pos, 1);
                if (!page) {
                    ret = -E2BIG;
                    goto out;
                }

                if (kmapped_page) {
                    flush_kernel_dcache_page(kmapped_page);
                    kunmap(kmapped_page);
                    put_arg_page(kmapped_page);
                }
                kmapped_page = page;
                kaddr = kmap(kmapped_page);
                kpos = pos & PAGE_MASK;
                flush_arg_page(bprm, kpos, kmapped_page);
            }
            if (copy_from_user(kaddr+offset, str, bytes_to_copy)) {
                ret = -EFAULT;
                goto out;
            }
        }
    }
    ret = 0;
out:
    if (kmapped_page) {
        flush_kernel_dcache_page(kmapped_page);
        kunmap(kmapped_page);
        put_arg_page(kmapped_page);
    }
    return ret;
}

/*
 * Like copy_strings, but get argv and its values from kernel memory.
 */
int copy_strings_kernel(int argc, const char *const *__argv,
            struct linux_binprm *bprm)
{
    int r;
    mm_segment_t oldfs = get_fs();
    struct user_arg_ptr argv = {
        .ptr.native = (const char __user *const  __user *)__argv,
    };

    set_fs(KERNEL_DS);
    r = copy_strings(argc, argv, bprm);
    set_fs(oldfs);

    return r;
}
EXPORT_SYMBOL(copy_strings_kernel);

#ifdef CONFIG_MMU

/*
 * During bprm_mm_init(), we create a temporary stack at STACK_TOP_MAX.  Once
 * the binfmt code determines where the new stack should reside, we shift it to
 * its final location.  The process proceeds as follows:
 *
 * 1) Use shift to calculate the new vma endpoints.
 * 2) Extend vma to cover both the old and new ranges.  This ensures the
 *    arguments passed to subsequent functions are consistent.
 * 3) Move vma's page tables to the new range.
 * 4) Free up any cleared pgd range.
 * 5) Shrink the vma to cover only the new range.
 */
static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift)
{
    struct mm_struct *mm = vma->vm_mm;
    unsigned long old_start = vma->vm_start;
    unsigned long old_end = vma->vm_end;
    unsigned long length = old_end - old_start;
    unsigned long new_start = old_start - shift;
    unsigned long new_end = old_end - shift;
    struct mmu_gather tlb;

    BUG_ON(new_start > new_end);

    /*
     * ensure there are no vmas between where we want to go
     * and where we are
     */
    if (vma != find_vma(mm, new_start))
        return -EFAULT;

    /*
     * cover the whole range: [new_start, old_end)
     */
    if (vma_adjust(vma, new_start, old_end, vma->vm_pgoff, NULL))
        return -ENOMEM;

    /*
     * move the page tables downwards, on failure we rely on
     * process cleanup to remove whatever mess we made.
     */
    if (length != move_page_tables(vma, old_start,
                       vma, new_start, length, false))
        return -ENOMEM;

    lru_add_drain();
    tlb_gather_mmu(&tlb, mm, 0);
    if (new_end > old_start) {
        /*
         * when the old and new regions overlap clear from new_end.
         */
        free_pgd_range(&tlb, new_end, old_end, new_end,
            vma->vm_next ? vma->vm_next->vm_start : 0);
    } else {
        /*
         * otherwise, clean from old_start; this is done to not touch
         * the address space in [new_end, old_start) some architectures
         * have constraints on va-space that make this illegal (IA64) -
         * for the others its just a little faster.
         */
        free_pgd_range(&tlb, old_start, old_end, new_end,
            vma->vm_next ? vma->vm_next->vm_start : 0);
    }
    tlb_finish_mmu(&tlb, new_end, old_end);

    /*
     * Shrink the vma to just the new range.  Always succeeds.
     */
    vma_adjust(vma, new_start, new_end, vma->vm_pgoff, NULL);

    return 0;
}

/*
 * Finalizes the stack vm_area_struct. The flags and permissions are updated,
 * the stack is optionally relocated, and some extra space is added.
 */
int setup_arg_pages(struct linux_binprm *bprm,
            unsigned long stack_top,
            int executable_stack)
{
    unsigned long ret;
    unsigned long stack_shift;
    struct mm_struct *mm = current->mm;
    struct vm_area_struct *vma = bprm->vma;
    struct vm_area_struct *prev = NULL;
    unsigned long vm_flags;
    unsigned long stack_base;
    unsigned long stack_size;
    unsigned long stack_expand;
    unsigned long rlim_stack;

#ifdef CONFIG_STACK_GROWSUP
    /* Limit stack size to 1GB */
    stack_base = rlimit_max(RLIMIT_STACK);
    if (stack_base > (1 << 30))
        stack_base = 1 << 30;

    /* Make sure we didn't let the argument array grow too large. */
    if (vma->vm_end - vma->vm_start > stack_base)
        return -ENOMEM;

    stack_base = PAGE_ALIGN(stack_top - stack_base);

    stack_shift = vma->vm_start - stack_base;
    mm->arg_start = bprm->p - stack_shift;
    bprm->p = vma->vm_end - stack_shift;
#else
    stack_top = arch_align_stack(stack_top);
    stack_top = PAGE_ALIGN(stack_top);

    if (unlikely(stack_top < mmap_min_addr) ||
        unlikely(vma->vm_end - vma->vm_start >= stack_top - mmap_min_addr))
        return -ENOMEM;

    stack_shift = vma->vm_end - stack_top;

    bprm->p -= stack_shift;
    mm->arg_start = bprm->p;
#endif

    if (bprm->loader)
        bprm->loader -= stack_shift;
    bprm->exec -= stack_shift;

    down_write(&mm->mmap_sem);
    vm_flags = VM_STACK_FLAGS;

    /*
     * Adjust stack execute permissions; explicitly enable for
     * EXSTACK_ENABLE_X, disable for EXSTACK_DISABLE_X and leave alone
     * (arch default) otherwise.
     */
    if (unlikely(executable_stack == EXSTACK_ENABLE_X))
        vm_flags |= VM_EXEC;
    else if (executable_stack == EXSTACK_DISABLE_X)
        vm_flags &= ~VM_EXEC;
    vm_flags |= mm->def_flags;
    vm_flags |= VM_STACK_INCOMPLETE_SETUP;

    ret = mprotect_fixup(vma, &prev, vma->vm_start, vma->vm_end,
            vm_flags);
    if (ret)
        goto out_unlock;
    BUG_ON(prev != vma);

    /* Move stack pages down in memory. */
    if (stack_shift) {
        ret = shift_arg_pages(vma, stack_shift);
        if (ret)
            goto out_unlock;
    }

    /* mprotect_fixup is overkill to remove the temporary stack flags */
    vma->vm_flags &= ~VM_STACK_INCOMPLETE_SETUP;

    stack_expand = 131072UL; /* randomly 32*4k (or 2*64k) pages */
    stack_size = vma->vm_end - vma->vm_start;
    /*
     * Align this down to a page boundary as expand_stack
     * will align it up.
     */
    rlim_stack = rlimit(RLIMIT_STACK) & PAGE_MASK;
#ifdef CONFIG_STACK_GROWSUP
    if (stack_size + stack_expand > rlim_stack)
        stack_base = vma->vm_start + rlim_stack;
    else
        stack_base = vma->vm_end + stack_expand;
#else
    if (stack_size + stack_expand > rlim_stack)
        stack_base = vma->vm_end - rlim_stack;
    else
        stack_base = vma->vm_start - stack_expand;
#endif
    current->mm->start_stack = bprm->p;
    ret = expand_stack(vma, stack_base);
    if (ret)
        ret = -EFAULT;

out_unlock:
    up_write(&mm->mmap_sem);
    return ret;
}
EXPORT_SYMBOL(setup_arg_pages);

#endif /* CONFIG_MMU */

struct file *open_exec(const char *name)
{
    struct file *file;
    int err;
    struct filename tmp = { .name = name };
    static const struct open_flags open_exec_flags = {
        .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC,
        .acc_mode = MAY_EXEC | MAY_OPEN,
        .intent = LOOKUP_OPEN
    };

    file = do_filp_open(AT_FDCWD, &tmp, &open_exec_flags, LOOKUP_FOLLOW);
    if (IS_ERR(file))
        goto out;

    err = -EACCES;
    if (!S_ISREG(file->f_path.dentry->d_inode->i_mode))
        goto exit;

    if (file->f_path.mnt->mnt_flags & MNT_NOEXEC)
        goto exit;

    fsnotify_open(file);

    err = deny_write_access(file);
    if (err)
        goto exit;

out:
    return file;

exit:
    fput(file);
    return ERR_PTR(err);
}
EXPORT_SYMBOL(open_exec);

int kernel_read(struct file *file, loff_t offset,
        char *addr, unsigned long count)
{
    mm_segment_t old_fs;
    loff_t pos = offset;
    int result;

    old_fs = get_fs();
    set_fs(get_ds());
    /* The cast to a user pointer is valid due to the set_fs() */
    result = vfs_read(file, (void __user *)addr, count, &pos);
    set_fs(old_fs);
    return result;
}

EXPORT_SYMBOL(kernel_read);

static int exec_mmap(struct mm_struct *mm)
{
    struct task_struct *tsk;
    struct mm_struct * old_mm, *active_mm;

    /* Notify parent that we're no longer interested in the old VM */
    tsk = current;
    old_mm = current->mm;
    mm_release(tsk, old_mm);

    if (old_mm) {
        sync_mm_rss(old_mm);
        /*
         * Make sure that if there is a core dump in progress
         * for the old mm, we get out and die instead of going
         * through with the exec.  We must hold mmap_sem around
         * checking core_state and changing tsk->mm.
         */
        down_read(&old_mm->mmap_sem);
        if (unlikely(old_mm->core_state)) {
            up_read(&old_mm->mmap_sem);
            return -EINTR;
        }
    }
    task_lock(tsk);
    active_mm = tsk->active_mm;
    tsk->mm = mm;
    tsk->active_mm = mm;
    activate_mm(active_mm, mm);
    task_unlock(tsk);
    arch_pick_mmap_layout(mm);
    if (old_mm) {
        up_read(&old_mm->mmap_sem);
        BUG_ON(active_mm != old_mm);
        setmax_mm_hiwater_rss(&tsk->signal->maxrss, old_mm);
        mm_update_next_owner(old_mm);
        mmput(old_mm);
        return 0;
    }
    mmdrop(active_mm);
    return 0;
}

/*
 * This function makes sure the current process has its own signal table,
 * so that flush_signal_handlers can later reset the handlers without
 * disturbing other processes.  (Other processes might share the signal
 * table via the CLONE_SIGHAND option to clone().)
 */
static int de_thread(struct task_struct *tsk)
{
    struct signal_struct *sig = tsk->signal;
    struct sighand_struct *oldsighand = tsk->sighand;
    spinlock_t *lock = &oldsighand->siglock;

    if (thread_group_empty(tsk))
        goto no_thread_group;

    /*
     * Kill all other threads in the thread group.
     */
    spin_lock_irq(lock);
    if (signal_group_exit(sig)) {
        /*
         * Another group action in progress, just
         * return so that the signal is processed.
         */
        spin_unlock_irq(lock);
        return -EAGAIN;
    }

    sig->group_exit_task = tsk;
    sig->notify_count = zap_other_threads(tsk);
    if (!thread_group_leader(tsk))
        sig->notify_count--;

    while (sig->notify_count) {
        __set_current_state(TASK_KILLABLE);
        spin_unlock_irq(lock);
        schedule();
        if (unlikely(__fatal_signal_pending(tsk)))
            goto killed;
        spin_lock_irq(lock);
    }
    spin_unlock_irq(lock);

    /*
     * At this point all other threads have exited, all we have to
     * do is to wait for the thread group leader to become inactive,
     * and to assume its PID:
     */
    if (!thread_group_leader(tsk)) {
        struct task_struct *leader = tsk->group_leader;

        sig->notify_count = -1; /* for exit_notify() */
        for (;;) {
            write_lock_irq(&tasklist_lock);
            if (likely(leader->exit_state))
                break;
            __set_current_state(TASK_KILLABLE);
            write_unlock_irq(&tasklist_lock);
            schedule();
            if (unlikely(__fatal_signal_pending(tsk)))
                goto killed;
        }

        /*
         * The only record we have of the real-time age of a
         * process, regardless of execs it's done, is start_time.
         * All the past CPU time is accumulated in signal_struct
         * from sister threads now dead.  But in this non-leader
         * exec, nothing survives from the original leader thread,
         * whose birth marks the true age of this process now.
         * When we take on its identity by switching to its PID, we
         * also take its birthdate (always earlier than our own).
         */
        tsk->start_time = leader->start_time;

        BUG_ON(!same_thread_group(leader, tsk));
        BUG_ON(has_group_leader_pid(tsk));
        /*
         * An exec() starts a new thread group with the
         * TGID of the previous thread group. Rehash the
         * two threads with a switched PID, and release
         * the former thread group leader:
         */

        /* Become a process group leader with the old leader's pid.
         * The old leader becomes a thread of the this thread group.
         * Note: The old leader also uses this pid until release_task
         *       is called.  Odd but simple and correct.
         */
        detach_pid(tsk, PIDTYPE_PID);
        tsk->pid = leader->pid;
        attach_pid(tsk, PIDTYPE_PID,  task_pid(leader));
        transfer_pid(leader, tsk, PIDTYPE_PGID);
        transfer_pid(leader, tsk, PIDTYPE_SID);

        list_replace_rcu(&leader->tasks, &tsk->tasks);
        list_replace_init(&leader->sibling, &tsk->sibling);

        tsk->group_leader = tsk;
        leader->group_leader = tsk;

        tsk->exit_signal = SIGCHLD;
        leader->exit_signal = -1;

        BUG_ON(leader->exit_state != EXIT_ZOMBIE);
        leader->exit_state = EXIT_DEAD;

        /*
         * We are going to release_task()->ptrace_unlink() silently,
         * the tracer can sleep in do_wait(). EXIT_DEAD guarantees
         * the tracer wont't block again waiting for this thread.
         */
        if (unlikely(leader->ptrace))
            __wake_up_parent(leader, leader->parent);
        write_unlock_irq(&tasklist_lock);

        release_task(leader);
    }

    sig->group_exit_task = NULL;
    sig->notify_count = 0;

no_thread_group:
    /* we have changed execution domain */
    tsk->exit_signal = SIGCHLD;

    exit_itimers(sig);
    flush_itimer_signals();

    if (atomic_read(&oldsighand->count) != 1) {
        struct sighand_struct *newsighand;
        /*
         * This ->sighand is shared with the CLONE_SIGHAND
         * but not CLONE_THREAD task, switch to the new one.
         */
        newsighand = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
        if (!newsighand)
            return -ENOMEM;

        atomic_set(&newsighand->count, 1);
        memcpy(newsighand->action, oldsighand->action,
               sizeof(newsighand->action));

        write_lock_irq(&tasklist_lock);
        spin_lock(&oldsighand->siglock);
        rcu_assign_pointer(tsk->sighand, newsighand);
        spin_unlock(&oldsighand->siglock);
        write_unlock_irq(&tasklist_lock);

        __cleanup_sighand(oldsighand);
    }

    BUG_ON(!thread_group_leader(tsk));
    return 0;

killed:
    /* protects against exit_notify() and __exit_signal() */
    read_lock(&tasklist_lock);
    sig->group_exit_task = NULL;
    sig->notify_count = 0;
    read_unlock(&tasklist_lock);
    return -EAGAIN;
}

char *get_task_comm(char *buf, struct task_struct *tsk)
{
    /* buf must be at least sizeof(tsk->comm) in size */
    task_lock(tsk);
    strncpy(buf, tsk->comm, sizeof(tsk->comm));
    task_unlock(tsk);
    return buf;
}
EXPORT_SYMBOL_GPL(get_task_comm);

/*
 * These functions flushes out all traces of the currently running executable
 * so that a new one can be started
 */

void set_task_comm(struct task_struct *tsk, char *buf)
{
    task_lock(tsk);

    trace_task_rename(tsk, buf);

    /*
     * Threads may access current->comm without holding
     * the task lock, so write the string carefully.
     * Readers without a lock may see incomplete new
     * names but are safe from non-terminating string reads.
     */
    memset(tsk->comm, 0, TASK_COMM_LEN);
    wmb();
    strlcpy(tsk->comm, buf, sizeof(tsk->comm));
    task_unlock(tsk);
    perf_event_comm(tsk);
}

static void filename_to_taskname(char *tcomm, const char *fn, unsigned int len)
{
    int i, ch;

    /* Copies the binary name from after last slash */
    for (i = 0; (ch = *(fn++)) != '\0';) {
        if (ch == '/')
            i = 0; /* overwrite what we wrote */
        else
            if (i < len - 1)
                tcomm[i++] = ch;
    }
    tcomm[i] = '\0';
}

int flush_old_exec(struct linux_binprm * bprm)
{
    int retval;

    /*
     * Make sure we have a private signal table and that
     * we are unassociated from the previous thread group.
     */
    retval = de_thread(current);
    if (retval)
        goto out;

    set_mm_exe_file(bprm->mm, bprm->file);

    filename_to_taskname(bprm->tcomm, bprm->filename, sizeof(bprm->tcomm));
    /*
     * Release all of the old mmap stuff
     */
    acct_arg_size(bprm, 0);
    retval = exec_mmap(bprm->mm);
    if (retval)
        goto out;

    bprm->mm = NULL;        /* We're using it now */

    set_fs(USER_DS);
    current->flags &=
        ~(PF_RANDOMIZE | PF_FORKNOEXEC | PF_KTHREAD | PF_NOFREEZE);
    flush_thread();
    current->personality &= ~bprm->per_clear;

    return 0;

out:
    return retval;
}
EXPORT_SYMBOL(flush_old_exec);

void would_dump(struct linux_binprm *bprm, struct file *file)
{
    if (inode_permission(file->f_path.dentry->d_inode, MAY_READ) < 0)
        bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
}
EXPORT_SYMBOL(would_dump);

void setup_new_exec(struct linux_binprm * bprm)
{
    arch_pick_mmap_layout(current->mm);

    /* This is the point of no return */
    current->sas_ss_sp = current->sas_ss_size = 0;

    if (uid_eq(current_euid(), current_uid()) && gid_eq(current_egid(), current_gid()))
        set_dumpable(current->mm, SUID_DUMPABLE_ENABLED);
    else
        set_dumpable(current->mm, suid_dumpable);

    set_task_comm(current, bprm->tcomm);

    /* Set the new mm task size. We have to do that late because it may
     * depend on TIF_32BIT which is only updated in flush_thread() on
     * some architectures like powerpc
     */
    current->mm->task_size = TASK_SIZE;

    /* install the new credentials */
    if (!uid_eq(bprm->cred->uid, current_euid()) ||
        !gid_eq(bprm->cred->gid, current_egid())) {
        current->pdeath_signal = 0;
    } else {
        would_dump(bprm, bprm->file);
        if (bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP)
            set_dumpable(current->mm, suid_dumpable);
    }

    /*
     * Flush performance counters when crossing a
     * security domain:
     */
    if (!get_dumpable(current->mm))
        perf_event_exit_task(current);

    /* An exec changes our domain. We are no longer part of the thread
       group */

    current->self_exec_id++;
            
    flush_signal_handlers(current, 0);
    do_close_on_exec(current->files);
}
EXPORT_SYMBOL(setup_new_exec);

/*
 * Prepare credentials and lock ->cred_guard_mutex.
 * install_exec_creds() commits the new creds and drops the lock.
 * Or, if exec fails before, free_bprm() should release ->cred and
 * and unlock.
 */
int prepare_bprm_creds(struct linux_binprm *bprm)
{
    if (mutex_lock_interruptible(&current->signal->cred_guard_mutex))
        return -ERESTARTNOINTR;

    bprm->cred = prepare_exec_creds();
    if (likely(bprm->cred))
        return 0;

    mutex_unlock(&current->signal->cred_guard_mutex);
    return -ENOMEM;
}

void free_bprm(struct linux_binprm *bprm)
{
    free_arg_pages(bprm);
    if (bprm->cred) {
        mutex_unlock(&current->signal->cred_guard_mutex);
        abort_creds(bprm->cred);
    }
    kfree(bprm);
}

/*
 * install the new credentials for this executable
 */
void install_exec_creds(struct linux_binprm *bprm)
{
    security_bprm_committing_creds(bprm);

    commit_creds(bprm->cred);
    bprm->cred = NULL;
    /*
     * cred_guard_mutex must be held at least to this point to prevent
     * ptrace_attach() from altering our determination of the task's
     * credentials; any time after this it may be unlocked.
     */
    security_bprm_committed_creds(bprm);
    mutex_unlock(&current->signal->cred_guard_mutex);
}
EXPORT_SYMBOL(install_exec_creds);

/*
 * determine how safe it is to execute the proposed program
 * - the caller must hold ->cred_guard_mutex to protect against
 *   PTRACE_ATTACH
 */
static int check_unsafe_exec(struct linux_binprm *bprm)
{
    struct task_struct *p = current, *t;
    unsigned n_fs;
    int res = 0;

    if (p->ptrace) {
        if (p->ptrace & PT_PTRACE_CAP)
            bprm->unsafe |= LSM_UNSAFE_PTRACE_CAP;
        else
            bprm->unsafe |= LSM_UNSAFE_PTRACE;
    }

    /*
     * This isn't strictly necessary, but it makes it harder for LSMs to
     * mess up.
     */
    if (current->no_new_privs)
        bprm->unsafe |= LSM_UNSAFE_NO_NEW_PRIVS;

    n_fs = 1;
    spin_lock(&p->fs->lock);
    rcu_read_lock();
    for (t = next_thread(p); t != p; t = next_thread(t)) {
        if (t->fs == p->fs)
            n_fs++;
    }
    rcu_read_unlock();

    if (p->fs->users > n_fs) {
        bprm->unsafe |= LSM_UNSAFE_SHARE;
    } else {
        res = -EAGAIN;
        if (!p->fs->in_exec) {
            p->fs->in_exec = 1;
            res = 1;
        }
    }
    spin_unlock(&p->fs->lock);

    return res;
}

/* 
 * Fill the binprm structure from the inode. 
 * Check permissions, then read the first 128 (BINPRM_BUF_SIZE) bytes
 *
 * This may be called multiple times for binary chains (scripts for example).
 */
int prepare_binprm(struct linux_binprm *bprm)
{
    umode_t mode;
    struct inode * inode = bprm->file->f_path.dentry->d_inode;
    int retval;

    mode = inode->i_mode;
    if (bprm->file->f_op == NULL)
        return -EACCES;

    /* clear any previous set[ug]id data from a previous binary */
    bprm->cred->euid = current_euid();
    bprm->cred->egid = current_egid();

    if (!(bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) &&
        !current->no_new_privs) {
        /* Set-uid? */
        if (mode & S_ISUID) {
            if (!kuid_has_mapping(bprm->cred->user_ns, inode->i_uid))
                return -EPERM;
            bprm->per_clear |= PER_CLEAR_ON_SETID;
            bprm->cred->euid = inode->i_uid;

        }

        /* Set-gid? */
        /*
         * If setgid is set but no group execute bit then this
         * is a candidate for mandatory locking, not a setgid
         * executable.
         */
        if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
            if (!kgid_has_mapping(bprm->cred->user_ns, inode->i_gid))
                return -EPERM;
            bprm->per_clear |= PER_CLEAR_ON_SETID;
            bprm->cred->egid = inode->i_gid;
        }
    }

    /* fill in binprm security blob */
    retval = security_bprm_set_creds(bprm);
    if (retval)
        return retval;
    bprm->cred_prepared = 1;

    memset(bprm->buf, 0, BINPRM_BUF_SIZE);
    return kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
}

EXPORT_SYMBOL(prepare_binprm);

/*
 * Arguments are '\0' separated strings found at the location bprm->p
 * points to; chop off the first by relocating brpm->p to right after
 * the first '\0' encountered.
 */
int remove_arg_zero(struct linux_binprm *bprm)
{
    int ret = 0;
    unsigned long offset;
    char *kaddr;
    struct page *page;

    if (!bprm->argc)
        return 0;

    do {
        offset = bprm->p & ~PAGE_MASK;
        page = get_arg_page(bprm, bprm->p, 0);
        if (!page) {
            ret = -EFAULT;
            goto out;
        }
        kaddr = kmap_atomic(page);

        for (; offset < PAGE_SIZE && kaddr[offset];
                offset++, bprm->p++)
            ;

        kunmap_atomic(kaddr);
        put_arg_page(page);

        if (offset == PAGE_SIZE)
            free_arg_page(bprm, (bprm->p >> PAGE_SHIFT) - 1);
    } while (offset == PAGE_SIZE);

    bprm->p++;
    bprm->argc--;
    ret = 0;

out:
    return ret;
}
EXPORT_SYMBOL(remove_arg_zero);

/*
 * cycle the list of binary formats handler, until one recognizes the image
 */
int search_binary_handler(struct linux_binprm *bprm,struct pt_regs *regs)
{
    unsigned int depth = bprm->recursion_depth;
    int try,retval;
    struct linux_binfmt *fmt;
    pid_t old_pid, old_vpid;

    retval = security_bprm_check(bprm);
    if (retval)
        return retval;

    retval = audit_bprm(bprm);
    if (retval)
        return retval;

    /* Need to fetch pid before load_binary changes it */
    old_pid = current->pid;
    rcu_read_lock();
    old_vpid = task_pid_nr_ns(current, task_active_pid_ns(current->parent));
    rcu_read_unlock();

    retval = -ENOENT;
    for (try=0; try<2; try++) {
        read_lock(&binfmt_lock);
        list_for_each_entry(fmt, &formats, lh) {
            int (*fn)(struct linux_binprm *, struct pt_regs *) = fmt->load_binary;
            if (!fn)
                continue;
            if (!try_module_get(fmt->module))
                continue;
            read_unlock(&binfmt_lock);
            retval = fn(bprm, regs);
            /*
             * Restore the depth counter to its starting value
             * in this call, so we don't have to rely on every
             * load_binary function to restore it on return.
             */
            bprm->recursion_depth = depth;
            if (retval >= 0) {
                if (depth == 0) {
                    trace_sched_process_exec(current, old_pid, bprm);
                    ptrace_event(PTRACE_EVENT_EXEC, old_vpid);
                }
                put_binfmt(fmt);
                allow_write_access(bprm->file);
                if (bprm->file)
                    fput(bprm->file);
                bprm->file = NULL;
                current->did_exec = 1;
                proc_exec_connector(current);
                return retval;
            }
            read_lock(&binfmt_lock);
            put_binfmt(fmt);
            if (retval != -ENOEXEC || bprm->mm == NULL)
                break;
            if (!bprm->file) {
                read_unlock(&binfmt_lock);
                return retval;
            }
        }
        read_unlock(&binfmt_lock);
#ifdef CONFIG_MODULES
        if (retval != -ENOEXEC || bprm->mm == NULL) {
            break;
        } else {
#define printable(c) (((c)=='\t') || ((c)=='\n') || (0x20<=(c) && (c)<=0x7e))
            if (printable(bprm->buf[0]) &&
                printable(bprm->buf[1]) &&
                printable(bprm->buf[2]) &&
                printable(bprm->buf[3]))
                break; /* -ENOEXEC */
            if (try)
                break; /* -ENOEXEC */
            request_module("binfmt-%04x", *(unsigned short *)(&bprm->buf[2]));
        }
#else
        break;
#endif
    }
    return retval;
}

EXPORT_SYMBOL(search_binary_handler);

/*
 * sys_execve() executes a new program.
 */
static int do_execve_common(const char *filename,
                struct user_arg_ptr argv,
                struct user_arg_ptr envp,
                struct pt_regs *regs)
{
    struct linux_binprm *bprm;
    struct file *file;
    struct files_struct *displaced;
    bool clear_in_exec;
    int retval;
    const struct cred *cred = current_cred();

    /*
     * We move the actual failure in case of RLIMIT_NPROC excess from
     * set*uid() to execve() because too many poorly written programs
     * don't check setuid() return code.  Here we additionally recheck
     * whether NPROC limit is still exceeded.
     */
    if ((current->flags & PF_NPROC_EXCEEDED) &&
        atomic_read(&cred->user->processes) > rlimit(RLIMIT_NPROC)) {
        retval = -EAGAIN;
        goto out_ret;
    }

    /* We're below the limit (still or again), so we don't want to make
     * further execve() calls fail. */
    current->flags &= ~PF_NPROC_EXCEEDED;

    retval = unshare_files(&displaced);
    if (retval)
        goto out_ret;

    retval = -ENOMEM;
    bprm = kzalloc(sizeof(*bprm), GFP_KERNEL);
    if (!bprm)
        goto out_files;

    retval = prepare_bprm_creds(bprm);
    if (retval)
        goto out_free;

    retval = check_unsafe_exec(bprm);
    if (retval < 0)
        goto out_free;
    clear_in_exec = retval;
    current->in_execve = 1;

    file = open_exec(filename);
    retval = PTR_ERR(file);
    if (IS_ERR(file))
        goto out_unmark;

    sched_exec();

    bprm->file = file;
    bprm->filename = filename;
    bprm->interp = filename;

    retval = bprm_mm_init(bprm);
    if (retval)
        goto out_file;

    bprm->argc = count(argv, MAX_ARG_STRINGS);
    if ((retval = bprm->argc) < 0)
        goto out;

    bprm->envc = count(envp, MAX_ARG_STRINGS);
    if ((retval = bprm->envc) < 0)
        goto out;

    retval = prepare_binprm(bprm);
    if (retval < 0)
        goto out;

    retval = copy_strings_kernel(1, &bprm->filename, bprm);
    if (retval < 0)
        goto out;

    bprm->exec = bprm->p;
    retval = copy_strings(bprm->envc, envp, bprm);
    if (retval < 0)
        goto out;

    retval = copy_strings(bprm->argc, argv, bprm);
    if (retval < 0)
        goto out;

    retval = search_binary_handler(bprm,regs);
    if (retval < 0)
        goto out;

    /* execve succeeded */
    current->fs->in_exec = 0;
    current->in_execve = 0;
    acct_update_integrals(current);
    free_bprm(bprm);
    if (displaced)
        put_files_struct(displaced);
    return retval;

out:
    if (bprm->mm) {
        acct_arg_size(bprm, 0);
        mmput(bprm->mm);
    }

out_file:
    if (bprm->file) {
        allow_write_access(bprm->file);
        fput(bprm->file);
    }

out_unmark:
    if (clear_in_exec)
        current->fs->in_exec = 0;
    current->in_execve = 0;

out_free:
    free_bprm(bprm);

out_files:
    if (displaced)
        reset_files_struct(displaced);
out_ret:
    return retval;
}

int do_execve(const char *filename,
    const char __user *const __user *__argv,
    const char __user *const __user *__envp,
    struct pt_regs *regs)
{
    struct user_arg_ptr argv = { .ptr.native = __argv };
    struct user_arg_ptr envp = { .ptr.native = __envp };
    return do_execve_common(filename, argv, envp, regs);
}

#ifdef CONFIG_COMPAT
int compat_do_execve(const char *filename,
    const compat_uptr_t __user *__argv,
    const compat_uptr_t __user *__envp,
    struct pt_regs *regs)
{
    struct user_arg_ptr argv = {
        .is_compat = true,
        .ptr.compat = __argv,
    };
    struct user_arg_ptr envp = {
        .is_compat = true,
        .ptr.compat = __envp,
    };
    return do_execve_common(filename, argv, envp, regs);
}
#endif

void set_binfmt(struct linux_binfmt *new)
{
    struct mm_struct *mm = current->mm;

    if (mm->binfmt)
        module_put(mm->binfmt->module);

    mm->binfmt = new;
    if (new)
        __module_get(new->module);
}

EXPORT_SYMBOL(set_binfmt);

/*
 * set_dumpable converts traditional three-value dumpable to two flags and
 * stores them into mm->flags.  It modifies lower two bits of mm->flags, but
 * these bits are not changed atomically.  So get_dumpable can observe the
 * intermediate state.  To avoid doing unexpected behavior, get get_dumpable
 * return either old dumpable or new one by paying attention to the order of
 * modifying the bits.
 *
 * dumpable |   mm->flags (binary)
 * old  new | initial interim  final
 * ---------+-----------------------
 *  0    1  |   00      01      01
 *  0    2  |   00      10(*)   11
 *  1    0  |   01      00      00
 *  1    2  |   01      11      11
 *  2    0  |   11      10(*)   00
 *  2    1  |   11      11      01
 *
 * (*) get_dumpable regards interim value of 10 as 11.
 */
void set_dumpable(struct mm_struct *mm, int value)
{
    switch (value) {
    case SUID_DUMPABLE_DISABLED:
        clear_bit(MMF_DUMPABLE, &mm->flags);
        smp_wmb();
        clear_bit(MMF_DUMP_SECURELY, &mm->flags);
        break;
    case SUID_DUMPABLE_ENABLED:
        set_bit(MMF_DUMPABLE, &mm->flags);
        smp_wmb();
        clear_bit(MMF_DUMP_SECURELY, &mm->flags);
        break;
    case SUID_DUMPABLE_SAFE:
        set_bit(MMF_DUMP_SECURELY, &mm->flags);
        smp_wmb();
        set_bit(MMF_DUMPABLE, &mm->flags);
        break;
    }
}

int __get_dumpable(unsigned long mm_flags)
{
    int ret;

    ret = mm_flags & MMF_DUMPABLE_MASK;
    return (ret > SUID_DUMPABLE_ENABLED) ? SUID_DUMPABLE_SAFE : ret;
}

int get_dumpable(struct mm_struct *mm)
{
    return __get_dumpable(mm->flags);
}

#ifdef __ARCH_WANT_SYS_EXECVE
SYSCALL_DEFINE3(execve,
        const char __user *, filename,
        const char __user *const __user *, argv,
        const char __user *const __user *, envp)
{
    struct filename *path = getname(filename);
    int error = PTR_ERR(path);
    if (!IS_ERR(path)) {
        error = do_execve(path->name, argv, envp, current_pt_regs());
        putname(path);
    }
    return error;
}
#ifdef CONFIG_COMPAT
asmlinkage long compat_sys_execve(const char __user * filename,
    const compat_uptr_t __user * argv,
    const compat_uptr_t __user * envp)
{
    struct filename *path = getname(filename);
    int error = PTR_ERR(path);
    if (!IS_ERR(path)) {
        error = compat_do_execve(path->name, argv, envp,
                            current_pt_regs());
        putname(path);
    }
    return error;
}
#endif
#endif

#ifdef __ARCH_WANT_KERNEL_EXECVE
int kernel_execve(const char *filename,
          const char *const argv[],
          const char *const envp[])
{
    struct pt_regs *p = current_pt_regs();
    int ret;

    ret = do_execve(filename,
            (const char __user *const __user *)argv,
            (const char __user *const __user *)envp, p);
    if (ret < 0)
        return ret;

    /*
     * We were successful.  We won't be returning to our caller, but
     * instead to user space by manipulating the kernel stack.
     */
    ret_from_kernel_execve(p);
}
#endif