coredump.c

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#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/coredump.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 <asm/exec.h>

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

#include <trace/events/sched.h>

int core_uses_pid;
char core_pattern[CORENAME_MAX_SIZE] = "core";
unsigned int core_pipe_limit;

struct core_name {
    char *corename;
    int used, size;
};
static atomic_t call_count = ATOMIC_INIT(1);

/* The maximal length of core_pattern is also specified in sysctl.c */

static int expand_corename(struct core_name *cn)
{
    char *old_corename = cn->corename;

    cn->size = CORENAME_MAX_SIZE * atomic_inc_return(&call_count);
    cn->corename = krealloc(old_corename, cn->size, GFP_KERNEL);

    if (!cn->corename) {
        kfree(old_corename);
        return -ENOMEM;
    }

    return 0;
}

static int cn_printf(struct core_name *cn, const char *fmt, ...)
{
    char *cur;
    int need;
    int ret;
    va_list arg;

    va_start(arg, fmt);
    need = vsnprintf(NULL, 0, fmt, arg);
    va_end(arg);

    if (likely(need < cn->size - cn->used - 1))
        goto out_printf;

    ret = expand_corename(cn);
    if (ret)
        goto expand_fail;

out_printf:
    cur = cn->corename + cn->used;
    va_start(arg, fmt);
    vsnprintf(cur, need + 1, fmt, arg);
    va_end(arg);
    cn->used += need;
    return 0;

expand_fail:
    return ret;
}

static void cn_escape(char *str)
{
    for (; *str; str++)
        if (*str == '/')
            *str = '!';
}

static int cn_print_exe_file(struct core_name *cn)
{
    struct file *exe_file;
    char *pathbuf, *path;
    int ret;

    exe_file = get_mm_exe_file(current->mm);
    if (!exe_file) {
        char *commstart = cn->corename + cn->used;
        ret = cn_printf(cn, "%s (path unknown)", current->comm);
        cn_escape(commstart);
        return ret;
    }

    pathbuf = kmalloc(PATH_MAX, GFP_TEMPORARY);
    if (!pathbuf) {
        ret = -ENOMEM;
        goto put_exe_file;
    }

    path = d_path(&exe_file->f_path, pathbuf, PATH_MAX);
    if (IS_ERR(path)) {
        ret = PTR_ERR(path);
        goto free_buf;
    }

    cn_escape(path);

    ret = cn_printf(cn, "%s", path);

free_buf:
    kfree(pathbuf);
put_exe_file:
    fput(exe_file);
    return ret;
}

/* format_corename will inspect the pattern parameter, and output a
 * name into corename, which must have space for at least
 * CORENAME_MAX_SIZE bytes plus one byte for the zero terminator.
 */
static int format_corename(struct core_name *cn, struct coredump_params *cprm)
{
    const struct cred *cred = current_cred();
    const char *pat_ptr = core_pattern;
    int ispipe = (*pat_ptr == '|');
    int pid_in_pattern = 0;
    int err = 0;

    cn->size = CORENAME_MAX_SIZE * atomic_read(&call_count);
    cn->corename = kmalloc(cn->size, GFP_KERNEL);
    cn->used = 0;

    if (!cn->corename)
        return -ENOMEM;

    /* Repeat as long as we have more pattern to process and more output
       space */
    while (*pat_ptr) {
        if (*pat_ptr != '%') {
            if (*pat_ptr == 0)
                goto out;
            err = cn_printf(cn, "%c", *pat_ptr++);
        } else {
            switch (*++pat_ptr) {
            /* single % at the end, drop that */
            case 0:
                goto out;
            /* Double percent, output one percent */
            case '%':
                err = cn_printf(cn, "%c", '%');
                break;
            /* pid */
            case 'p':
                pid_in_pattern = 1;
                err = cn_printf(cn, "%d",
                          task_tgid_vnr(current));
                break;
            /* uid */
            case 'u':
                err = cn_printf(cn, "%d", cred->uid);
                break;
            /* gid */
            case 'g':
                err = cn_printf(cn, "%d", cred->gid);
                break;
            case 'd':
                err = cn_printf(cn, "%d",
                    __get_dumpable(cprm->mm_flags));
                break;
            /* signal that caused the coredump */
            case 's':
                err = cn_printf(cn, "%ld", cprm->siginfo->si_signo);
                break;
            /* UNIX time of coredump */
            case 't': {
                struct timeval tv;
                do_gettimeofday(&tv);
                err = cn_printf(cn, "%lu", tv.tv_sec);
                break;
            }
            /* hostname */
            case 'h': {
                char *namestart = cn->corename + cn->used;
                down_read(&uts_sem);
                err = cn_printf(cn, "%s",
                          utsname()->nodename);
                up_read(&uts_sem);
                cn_escape(namestart);
                break;
            }
            /* executable */
            case 'e': {
                char *commstart = cn->corename + cn->used;
                err = cn_printf(cn, "%s", current->comm);
                cn_escape(commstart);
                break;
            }
            case 'E':
                err = cn_print_exe_file(cn);
                break;
            /* core limit size */
            case 'c':
                err = cn_printf(cn, "%lu",
                          rlimit(RLIMIT_CORE));
                break;
            default:
                break;
            }
            ++pat_ptr;
        }

        if (err)
            return err;
    }

    /* Backward compatibility with core_uses_pid:
     *
     * If core_pattern does not include a %p (as is the default)
     * and core_uses_pid is set, then .%pid will be appended to
     * the filename. Do not do this for piped commands. */
    if (!ispipe && !pid_in_pattern && core_uses_pid) {
        err = cn_printf(cn, ".%d", task_tgid_vnr(current));
        if (err)
            return err;
    }
out:
    return ispipe;
}

static int zap_process(struct task_struct *start, int exit_code)
{
    struct task_struct *t;
    int nr = 0;

    start->signal->flags = SIGNAL_GROUP_EXIT;
    start->signal->group_exit_code = exit_code;
    start->signal->group_stop_count = 0;

    t = start;
    do {
        task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
        if (t != current && t->mm) {
            sigaddset(&t->pending.signal, SIGKILL);
            signal_wake_up(t, 1);
            nr++;
        }
    } while_each_thread(start, t);

    return nr;
}

static inline int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
                struct core_state *core_state, int exit_code)
{
    struct task_struct *g, *p;
    unsigned long flags;
    int nr = -EAGAIN;

    spin_lock_irq(&tsk->sighand->siglock);
    if (!signal_group_exit(tsk->signal)) {
        mm->core_state = core_state;
        nr = zap_process(tsk, exit_code);
    }
    spin_unlock_irq(&tsk->sighand->siglock);
    if (unlikely(nr < 0))
        return nr;

    if (atomic_read(&mm->mm_users) == nr + 1)
        goto done;
    /*
     * We should find and kill all tasks which use this mm, and we should
     * count them correctly into ->nr_threads. We don't take tasklist
     * lock, but this is safe wrt:
     *
     * fork:
     *  None of sub-threads can fork after zap_process(leader). All
     *  processes which were created before this point should be
     *  visible to zap_threads() because copy_process() adds the new
     *  process to the tail of init_task.tasks list, and lock/unlock
     *  of ->siglock provides a memory barrier.
     *
     * do_exit:
     *  The caller holds mm->mmap_sem. This means that the task which
     *  uses this mm can't pass exit_mm(), so it can't exit or clear
     *  its ->mm.
     *
     * de_thread:
     *  It does list_replace_rcu(&leader->tasks, &current->tasks),
     *  we must see either old or new leader, this does not matter.
     *  However, it can change p->sighand, so lock_task_sighand(p)
     *  must be used. Since p->mm != NULL and we hold ->mmap_sem
     *  it can't fail.
     *
     *  Note also that "g" can be the old leader with ->mm == NULL
     *  and already unhashed and thus removed from ->thread_group.
     *  This is OK, __unhash_process()->list_del_rcu() does not
     *  clear the ->next pointer, we will find the new leader via
     *  next_thread().
     */
    rcu_read_lock();
    for_each_process(g) {
        if (g == tsk->group_leader)
            continue;
        if (g->flags & PF_KTHREAD)
            continue;
        p = g;
        do {
            if (p->mm) {
                if (unlikely(p->mm == mm)) {
                    lock_task_sighand(p, &flags);
                    nr += zap_process(p, exit_code);
                    unlock_task_sighand(p, &flags);
                }
                break;
            }
        } while_each_thread(g, p);
    }
    rcu_read_unlock();
done:
    atomic_set(&core_state->nr_threads, nr);
    return nr;
}

static int coredump_wait(int exit_code, struct core_state *core_state)
{
    struct task_struct *tsk = current;
    struct mm_struct *mm = tsk->mm;
    int core_waiters = -EBUSY;

    init_completion(&core_state->startup);
    core_state->dumper.task = tsk;
    core_state->dumper.next = NULL;

    down_write(&mm->mmap_sem);
    if (!mm->core_state)
        core_waiters = zap_threads(tsk, mm, core_state, exit_code);
    up_write(&mm->mmap_sem);

    if (core_waiters > 0) {
        struct core_thread *ptr;

        wait_for_completion(&core_state->startup);
        /*
         * Wait for all the threads to become inactive, so that
         * all the thread context (extended register state, like
         * fpu etc) gets copied to the memory.
         */
        ptr = core_state->dumper.next;
        while (ptr != NULL) {
            wait_task_inactive(ptr->task, 0);
            ptr = ptr->next;
        }
    }

    return core_waiters;
}

static void coredump_finish(struct mm_struct *mm)
{
    struct core_thread *curr, *next;
    struct task_struct *task;

    next = mm->core_state->dumper.next;
    while ((curr = next) != NULL) {
        next = curr->next;
        task = curr->task;
        /*
         * see exit_mm(), curr->task must not see
         * ->task == NULL before we read ->next.
         */
        smp_mb();
        curr->task = NULL;
        wake_up_process(task);
    }

    mm->core_state = NULL;
}

static void wait_for_dump_helpers(struct file *file)
{
    struct pipe_inode_info *pipe;

    pipe = file->f_path.dentry->d_inode->i_pipe;

    pipe_lock(pipe);
    pipe->readers++;
    pipe->writers--;

    while ((pipe->readers > 1) && (!signal_pending(current))) {
        wake_up_interruptible_sync(&pipe->wait);
        kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
        pipe_wait(pipe);
    }

    pipe->readers--;
    pipe->writers++;
    pipe_unlock(pipe);

}

/*
 * umh_pipe_setup
 * helper function to customize the process used
 * to collect the core in userspace.  Specifically
 * it sets up a pipe and installs it as fd 0 (stdin)
 * for the process.  Returns 0 on success, or
 * PTR_ERR on failure.
 * Note that it also sets the core limit to 1.  This
 * is a special value that we use to trap recursive
 * core dumps
 */
static int umh_pipe_setup(struct subprocess_info *info, struct cred *new)
{
    struct file *files[2];
    struct coredump_params *cp = (struct coredump_params *)info->data;
    int err = create_pipe_files(files, 0);
    if (err)
        return err;

    cp->file = files[1];

    err = replace_fd(0, files[0], 0);
    fput(files[0]);
    /* and disallow core files too */
    current->signal->rlim[RLIMIT_CORE] = (struct rlimit){1, 1};

    return err;
}

void do_coredump(siginfo_t *siginfo, struct pt_regs *regs)
{
    struct core_state core_state;
    struct core_name cn;
    struct mm_struct *mm = current->mm;
    struct linux_binfmt * binfmt;
    const struct cred *old_cred;
    struct cred *cred;
    int retval = 0;
    int flag = 0;
    int ispipe;
    struct files_struct *displaced;
    bool need_nonrelative = false;
    static atomic_t core_dump_count = ATOMIC_INIT(0);
    struct coredump_params cprm = {
        .siginfo = siginfo,
        .regs = regs,
        .limit = rlimit(RLIMIT_CORE),
        /*
         * We must use the same mm->flags while dumping core to avoid
         * inconsistency of bit flags, since this flag is not protected
         * by any locks.
         */
        .mm_flags = mm->flags,
    };

    audit_core_dumps(siginfo->si_signo);

    binfmt = mm->binfmt;
    if (!binfmt || !binfmt->core_dump)
        goto fail;
    if (!__get_dumpable(cprm.mm_flags))
        goto fail;

    cred = prepare_creds();
    if (!cred)
        goto fail;
    /*
     * We cannot trust fsuid as being the "true" uid of the process
     * nor do we know its entire history. We only know it was tainted
     * so we dump it as root in mode 2, and only into a controlled
     * environment (pipe handler or fully qualified path).
     */
    if (__get_dumpable(cprm.mm_flags) == SUID_DUMPABLE_SAFE) {
        /* Setuid core dump mode */
        flag = O_EXCL;      /* Stop rewrite attacks */
        cred->fsuid = GLOBAL_ROOT_UID;  /* Dump root private */
        need_nonrelative = true;
    }

    retval = coredump_wait(siginfo->si_signo, &core_state);
    if (retval < 0)
        goto fail_creds;

    old_cred = override_creds(cred);

    /*
     * Clear any false indication of pending signals that might
     * be seen by the filesystem code called to write the core file.
     */
    clear_thread_flag(TIF_SIGPENDING);

    ispipe = format_corename(&cn, &cprm);

    if (ispipe) {
        int dump_count;
        char **helper_argv;

        if (ispipe < 0) {
            printk(KERN_WARNING "format_corename failed\n");
            printk(KERN_WARNING "Aborting core\n");
            goto fail_corename;
        }

        if (cprm.limit == 1) {
            /* See umh_pipe_setup() which sets RLIMIT_CORE = 1.
             *
             * Normally core limits are irrelevant to pipes, since
             * we're not writing to the file system, but we use
             * cprm.limit of 1 here as a speacial value, this is a
             * consistent way to catch recursive crashes.
             * We can still crash if the core_pattern binary sets
             * RLIM_CORE = !1, but it runs as root, and can do
             * lots of stupid things.
             *
             * Note that we use task_tgid_vnr here to grab the pid
             * of the process group leader.  That way we get the
             * right pid if a thread in a multi-threaded
             * core_pattern process dies.
             */
            printk(KERN_WARNING
                "Process %d(%s) has RLIMIT_CORE set to 1\n",
                task_tgid_vnr(current), current->comm);
            printk(KERN_WARNING "Aborting core\n");
            goto fail_unlock;
        }
        cprm.limit = RLIM_INFINITY;

        dump_count = atomic_inc_return(&core_dump_count);
        if (core_pipe_limit && (core_pipe_limit < dump_count)) {
            printk(KERN_WARNING "Pid %d(%s) over core_pipe_limit\n",
                   task_tgid_vnr(current), current->comm);
            printk(KERN_WARNING "Skipping core dump\n");
            goto fail_dropcount;
        }

        helper_argv = argv_split(GFP_KERNEL, cn.corename+1, NULL);
        if (!helper_argv) {
            printk(KERN_WARNING "%s failed to allocate memory\n",
                   __func__);
            goto fail_dropcount;
        }

        retval = call_usermodehelper_fns(helper_argv[0], helper_argv,
                    NULL, UMH_WAIT_EXEC, umh_pipe_setup,
                    NULL, &cprm);
        argv_free(helper_argv);
        if (retval) {
            printk(KERN_INFO "Core dump to %s pipe failed\n",
                   cn.corename);
            goto close_fail;
        }
    } else {
        struct inode *inode;

        if (cprm.limit < binfmt->min_coredump)
            goto fail_unlock;

        if (need_nonrelative && cn.corename[0] != '/') {
            printk(KERN_WARNING "Pid %d(%s) can only dump core "\
                "to fully qualified path!\n",
                task_tgid_vnr(current), current->comm);
            printk(KERN_WARNING "Skipping core dump\n");
            goto fail_unlock;
        }

        cprm.file = filp_open(cn.corename,
                 O_CREAT | 2 | O_NOFOLLOW | O_LARGEFILE | flag,
                 0600);
        if (IS_ERR(cprm.file))
            goto fail_unlock;

        inode = cprm.file->f_path.dentry->d_inode;
        if (inode->i_nlink > 1)
            goto close_fail;
        if (d_unhashed(cprm.file->f_path.dentry))
            goto close_fail;
        /*
         * AK: actually i see no reason to not allow this for named
         * pipes etc, but keep the previous behaviour for now.
         */
        if (!S_ISREG(inode->i_mode))
            goto close_fail;
        /*
         * Dont allow local users get cute and trick others to coredump
         * into their pre-created files.
         */
        if (!uid_eq(inode->i_uid, current_fsuid()))
            goto close_fail;
        if (!cprm.file->f_op || !cprm.file->f_op->write)
            goto close_fail;
        if (do_truncate(cprm.file->f_path.dentry, 0, 0, cprm.file))
            goto close_fail;
    }

    /* get us an unshared descriptor table; almost always a no-op */
    retval = unshare_files(&displaced);
    if (retval)
        goto close_fail;
    if (displaced)
        put_files_struct(displaced);
    retval = binfmt->core_dump(&cprm);
    if (retval)
        current->signal->group_exit_code |= 0x80;

    if (ispipe && core_pipe_limit)
        wait_for_dump_helpers(cprm.file);
close_fail:
    if (cprm.file)
        filp_close(cprm.file, NULL);
fail_dropcount:
    if (ispipe)
        atomic_dec(&core_dump_count);
fail_unlock:
    kfree(cn.corename);
fail_corename:
    coredump_finish(mm);
    revert_creds(old_cred);
fail_creds:
    put_cred(cred);
fail:
    return;
}

/*
 * Core dumping helper functions.  These are the only things you should
 * do on a core-file: use only these functions to write out all the
 * necessary info.
 */
int dump_write(struct file *file, const void *addr, int nr)
{
    return access_ok(VERIFY_READ, addr, nr) && file->f_op->write(file, addr, nr, &file->f_pos) == nr;
}
EXPORT_SYMBOL(dump_write);

int dump_seek(struct file *file, loff_t off)
{
    int ret = 1;

    if (file->f_op->llseek && file->f_op->llseek != no_llseek) {
        if (file->f_op->llseek(file, off, SEEK_CUR) < 0)
            return 0;
    } else {
        char *buf = (char *)get_zeroed_page(GFP_KERNEL);

        if (!buf)
            return 0;
        while (off > 0) {
            unsigned long n = off;

            if (n > PAGE_SIZE)
                n = PAGE_SIZE;
            if (!dump_write(file, buf, n)) {
                ret = 0;
                break;
            }
            off -= n;
        }
        free_page((unsigned long)buf);
    }
    return ret;
}
EXPORT_SYMBOL(dump_seek);