fcntl.c

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

#include <linux/syscalls.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/capability.h>
#include <linux/dnotify.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/pipe_fs_i.h>
#include <linux/security.h>
#include <linux/ptrace.h>
#include <linux/signal.h>
#include <linux/rcupdate.h>
#include <linux/pid_namespace.h>
#include <linux/user_namespace.h>

#include <asm/poll.h>
#include <asm/siginfo.h>
#include <asm/uaccess.h>

#define SETFL_MASK (O_APPEND | O_NONBLOCK | O_NDELAY | O_DIRECT | O_NOATIME)

static int setfl(int fd, struct file * filp, unsigned long arg)
{
    struct inode * inode = filp->f_path.dentry->d_inode;
    int error = 0;

    /*
     * O_APPEND cannot be cleared if the file is marked as append-only
     * and the file is open for write.
     */
    if (((arg ^ filp->f_flags) & O_APPEND) && IS_APPEND(inode))
        return -EPERM;

    /* O_NOATIME can only be set by the owner or superuser */
    if ((arg & O_NOATIME) && !(filp->f_flags & O_NOATIME))
        if (!inode_owner_or_capable(inode))
            return -EPERM;

    /* required for strict SunOS emulation */
    if (O_NONBLOCK != O_NDELAY)
           if (arg & O_NDELAY)
           arg |= O_NONBLOCK;

    if (arg & O_DIRECT) {
        if (!filp->f_mapping || !filp->f_mapping->a_ops ||
            !filp->f_mapping->a_ops->direct_IO)
                return -EINVAL;
    }

    if (filp->f_op && filp->f_op->check_flags)
        error = filp->f_op->check_flags(arg);
    if (error)
        return error;

    /*
     * ->fasync() is responsible for setting the FASYNC bit.
     */
    if (((arg ^ filp->f_flags) & FASYNC) && filp->f_op &&
            filp->f_op->fasync) {
        error = filp->f_op->fasync(fd, filp, (arg & FASYNC) != 0);
        if (error < 0)
            goto out;
        if (error > 0)
            error = 0;
    }
    spin_lock(&filp->f_lock);
    filp->f_flags = (arg & SETFL_MASK) | (filp->f_flags & ~SETFL_MASK);
    spin_unlock(&filp->f_lock);

 out:
    return error;
}

static void f_modown(struct file *filp, struct pid *pid, enum pid_type type,
                     int force)
{
    write_lock_irq(&filp->f_owner.lock);
    if (force || !filp->f_owner.pid) {
        put_pid(filp->f_owner.pid);
        filp->f_owner.pid = get_pid(pid);
        filp->f_owner.pid_type = type;

        if (pid) {
            const struct cred *cred = current_cred();
            filp->f_owner.uid = cred->uid;
            filp->f_owner.euid = cred->euid;
        }
    }
    write_unlock_irq(&filp->f_owner.lock);
}

int __f_setown(struct file *filp, struct pid *pid, enum pid_type type,
        int force)
{
    int err;

    err = security_file_set_fowner(filp);
    if (err)
        return err;

    f_modown(filp, pid, type, force);
    return 0;
}
EXPORT_SYMBOL(__f_setown);

int f_setown(struct file *filp, unsigned long arg, int force)
{
    enum pid_type type;
    struct pid *pid;
    int who = arg;
    int result;
    type = PIDTYPE_PID;
    if (who < 0) {
        type = PIDTYPE_PGID;
        who = -who;
    }
    rcu_read_lock();
    pid = find_vpid(who);
    result = __f_setown(filp, pid, type, force);
    rcu_read_unlock();
    return result;
}
EXPORT_SYMBOL(f_setown);

void f_delown(struct file *filp)
{
    f_modown(filp, NULL, PIDTYPE_PID, 1);
}

pid_t f_getown(struct file *filp)
{
    pid_t pid;
    read_lock(&filp->f_owner.lock);
    pid = pid_vnr(filp->f_owner.pid);
    if (filp->f_owner.pid_type == PIDTYPE_PGID)
        pid = -pid;
    read_unlock(&filp->f_owner.lock);
    return pid;
}

static int f_setown_ex(struct file *filp, unsigned long arg)
{
    struct f_owner_ex __user *owner_p = (void __user *)arg;
    struct f_owner_ex owner;
    struct pid *pid;
    int type;
    int ret;

    ret = copy_from_user(&owner, owner_p, sizeof(owner));
    if (ret)
        return -EFAULT;

    switch (owner.type) {
    case F_OWNER_TID:
        type = PIDTYPE_MAX;
        break;

    case F_OWNER_PID:
        type = PIDTYPE_PID;
        break;

    case F_OWNER_PGRP:
        type = PIDTYPE_PGID;
        break;

    default:
        return -EINVAL;
    }

    rcu_read_lock();
    pid = find_vpid(owner.pid);
    if (owner.pid && !pid)
        ret = -ESRCH;
    else
        ret = __f_setown(filp, pid, type, 1);
    rcu_read_unlock();

    return ret;
}

static int f_getown_ex(struct file *filp, unsigned long arg)
{
    struct f_owner_ex __user *owner_p = (void __user *)arg;
    struct f_owner_ex owner;
    int ret = 0;

    read_lock(&filp->f_owner.lock);
    owner.pid = pid_vnr(filp->f_owner.pid);
    switch (filp->f_owner.pid_type) {
    case PIDTYPE_MAX:
        owner.type = F_OWNER_TID;
        break;

    case PIDTYPE_PID:
        owner.type = F_OWNER_PID;
        break;

    case PIDTYPE_PGID:
        owner.type = F_OWNER_PGRP;
        break;

    default:
        WARN_ON(1);
        ret = -EINVAL;
        break;
    }
    read_unlock(&filp->f_owner.lock);

    if (!ret) {
        ret = copy_to_user(owner_p, &owner, sizeof(owner));
        if (ret)
            ret = -EFAULT;
    }
    return ret;
}

#ifdef CONFIG_CHECKPOINT_RESTORE
static int f_getowner_uids(struct file *filp, unsigned long arg)
{
    struct user_namespace *user_ns = current_user_ns();
    uid_t __user *dst = (void __user *)arg;
    uid_t src[2];
    int err;

    read_lock(&filp->f_owner.lock);
    src[0] = from_kuid(user_ns, filp->f_owner.uid);
    src[1] = from_kuid(user_ns, filp->f_owner.euid);
    read_unlock(&filp->f_owner.lock);

    err  = put_user(src[0], &dst[0]);
    err |= put_user(src[1], &dst[1]);

    return err;
}
#else
static int f_getowner_uids(struct file *filp, unsigned long arg)
{
    return -EINVAL;
}
#endif

static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
        struct file *filp)
{
    long err = -EINVAL;

    switch (cmd) {
    case F_DUPFD:
        err = f_dupfd(arg, filp, 0);
        break;
    case F_DUPFD_CLOEXEC:
        err = f_dupfd(arg, filp, O_CLOEXEC);
        break;
    case F_GETFD:
        err = get_close_on_exec(fd) ? FD_CLOEXEC : 0;
        break;
    case F_SETFD:
        err = 0;
        set_close_on_exec(fd, arg & FD_CLOEXEC);
        break;
    case F_GETFL:
        err = filp->f_flags;
        break;
    case F_SETFL:
        err = setfl(fd, filp, arg);
        break;
    case F_GETLK:
        err = fcntl_getlk(filp, (struct flock __user *) arg);
        break;
    case F_SETLK:
    case F_SETLKW:
        err = fcntl_setlk(fd, filp, cmd, (struct flock __user *) arg);
        break;
    case F_GETOWN:
        /*
         * XXX If f_owner is a process group, the
         * negative return value will get converted
         * into an error.  Oops.  If we keep the
         * current syscall conventions, the only way
         * to fix this will be in libc.
         */
        err = f_getown(filp);
        force_successful_syscall_return();
        break;
    case F_SETOWN:
        err = f_setown(filp, arg, 1);
        break;
    case F_GETOWN_EX:
        err = f_getown_ex(filp, arg);
        break;
    case F_SETOWN_EX:
        err = f_setown_ex(filp, arg);
        break;
    case F_GETOWNER_UIDS:
        err = f_getowner_uids(filp, arg);
        break;
    case F_GETSIG:
        err = filp->f_owner.signum;
        break;
    case F_SETSIG:
        /* arg == 0 restores default behaviour. */
        if (!valid_signal(arg)) {
            break;
        }
        err = 0;
        filp->f_owner.signum = arg;
        break;
    case F_GETLEASE:
        err = fcntl_getlease(filp);
        break;
    case F_SETLEASE:
        err = fcntl_setlease(fd, filp, arg);
        break;
    case F_NOTIFY:
        err = fcntl_dirnotify(fd, filp, arg);
        break;
    case F_SETPIPE_SZ:
    case F_GETPIPE_SZ:
        err = pipe_fcntl(filp, cmd, arg);
        break;
    default:
        break;
    }
    return err;
}

static int check_fcntl_cmd(unsigned cmd)
{
    switch (cmd) {
    case F_DUPFD:
    case F_DUPFD_CLOEXEC:
    case F_GETFD:
    case F_SETFD:
    case F_GETFL:
        return 1;
    }
    return 0;
}

SYSCALL_DEFINE3(fcntl, unsigned int, fd, unsigned int, cmd, unsigned long, arg)
{   
    struct fd f = fdget_raw(fd);
    long err = -EBADF;

    if (!f.file)
        goto out;

    if (unlikely(f.file->f_mode & FMODE_PATH)) {
        if (!check_fcntl_cmd(cmd))
            goto out1;
    }

    err = security_file_fcntl(f.file, cmd, arg);
    if (!err)
        err = do_fcntl(fd, cmd, arg, f.file);

out1:
    fdput(f);
out:
    return err;
}

#if BITS_PER_LONG == 32
SYSCALL_DEFINE3(fcntl64, unsigned int, fd, unsigned int, cmd,
        unsigned long, arg)
{   
    struct fd f = fdget_raw(fd);
    long err = -EBADF;

    if (!f.file)
        goto out;

    if (unlikely(f.file->f_mode & FMODE_PATH)) {
        if (!check_fcntl_cmd(cmd))
            goto out1;
    }

    err = security_file_fcntl(f.file, cmd, arg);
    if (err)
        goto out1;
    
    switch (cmd) {
        case F_GETLK64:
            err = fcntl_getlk64(f.file, (struct flock64 __user *) arg);
            break;
        case F_SETLK64:
        case F_SETLKW64:
            err = fcntl_setlk64(fd, f.file, cmd,
                    (struct flock64 __user *) arg);
            break;
        default:
            err = do_fcntl(fd, cmd, arg, f.file);
            break;
    }
out1:
    fdput(f);
out:
    return err;
}
#endif

/* Table to convert sigio signal codes into poll band bitmaps */

static const long band_table[NSIGPOLL] = {
    POLLIN | POLLRDNORM,            /* POLL_IN */
    POLLOUT | POLLWRNORM | POLLWRBAND,  /* POLL_OUT */
    POLLIN | POLLRDNORM | POLLMSG,      /* POLL_MSG */
    POLLERR,                /* POLL_ERR */
    POLLPRI | POLLRDBAND,           /* POLL_PRI */
    POLLHUP | POLLERR           /* POLL_HUP */
};

static inline int sigio_perm(struct task_struct *p,
                             struct fown_struct *fown, int sig)
{
    const struct cred *cred;
    int ret;

    rcu_read_lock();
    cred = __task_cred(p);
    ret = ((uid_eq(fown->euid, GLOBAL_ROOT_UID) ||
        uid_eq(fown->euid, cred->suid) || uid_eq(fown->euid, cred->uid) ||
        uid_eq(fown->uid,  cred->suid) || uid_eq(fown->uid,  cred->uid)) &&
           !security_file_send_sigiotask(p, fown, sig));
    rcu_read_unlock();
    return ret;
}

static void send_sigio_to_task(struct task_struct *p,
                   struct fown_struct *fown,
                   int fd, int reason, int group)
{
    /*
     * F_SETSIG can change ->signum lockless in parallel, make
     * sure we read it once and use the same value throughout.
     */
    int signum = ACCESS_ONCE(fown->signum);

    if (!sigio_perm(p, fown, signum))
        return;

    switch (signum) {
        siginfo_t si;
        default:
            /* Queue a rt signal with the appropriate fd as its
               value.  We use SI_SIGIO as the source, not 
               SI_KERNEL, since kernel signals always get 
               delivered even if we can't queue.  Failure to
               queue in this case _should_ be reported; we fall
               back to SIGIO in that case. --sct */
            si.si_signo = signum;
            si.si_errno = 0;
                si.si_code  = reason;
            /* Make sure we are called with one of the POLL_*
               reasons, otherwise we could leak kernel stack into
               userspace.  */
            BUG_ON((reason & __SI_MASK) != __SI_POLL);
            if (reason - POLL_IN >= NSIGPOLL)
                si.si_band  = ~0L;
            else
                si.si_band = band_table[reason - POLL_IN];
            si.si_fd    = fd;
            if (!do_send_sig_info(signum, &si, p, group))
                break;
        /* fall-through: fall back on the old plain SIGIO signal */
        case 0:
            do_send_sig_info(SIGIO, SEND_SIG_PRIV, p, group);
    }
}

void send_sigio(struct fown_struct *fown, int fd, int band)
{
    struct task_struct *p;
    enum pid_type type;
    struct pid *pid;
    int group = 1;
    
    read_lock(&fown->lock);

    type = fown->pid_type;
    if (type == PIDTYPE_MAX) {
        group = 0;
        type = PIDTYPE_PID;
    }

    pid = fown->pid;
    if (!pid)
        goto out_unlock_fown;
    
    read_lock(&tasklist_lock);
    do_each_pid_task(pid, type, p) {
        send_sigio_to_task(p, fown, fd, band, group);
    } while_each_pid_task(pid, type, p);
    read_unlock(&tasklist_lock);
 out_unlock_fown:
    read_unlock(&fown->lock);
}

static void send_sigurg_to_task(struct task_struct *p,
                struct fown_struct *fown, int group)
{
    if (sigio_perm(p, fown, SIGURG))
        do_send_sig_info(SIGURG, SEND_SIG_PRIV, p, group);
}

int send_sigurg(struct fown_struct *fown)
{
    struct task_struct *p;
    enum pid_type type;
    struct pid *pid;
    int group = 1;
    int ret = 0;
    
    read_lock(&fown->lock);

    type = fown->pid_type;
    if (type == PIDTYPE_MAX) {
        group = 0;
        type = PIDTYPE_PID;
    }

    pid = fown->pid;
    if (!pid)
        goto out_unlock_fown;

    ret = 1;
    
    read_lock(&tasklist_lock);
    do_each_pid_task(pid, type, p) {
        send_sigurg_to_task(p, fown, group);
    } while_each_pid_task(pid, type, p);
    read_unlock(&tasklist_lock);
 out_unlock_fown:
    read_unlock(&fown->lock);
    return ret;
}

static DEFINE_SPINLOCK(fasync_lock);
static struct kmem_cache *fasync_cache __read_mostly;

static void fasync_free_rcu(struct rcu_head *head)
{
    kmem_cache_free(fasync_cache,
            container_of(head, struct fasync_struct, fa_rcu));
}

/*
 * Remove a fasync entry. If successfully removed, return
 * positive and clear the FASYNC flag. If no entry exists,
 * do nothing and return 0.
 *
 * NOTE! It is very important that the FASYNC flag always
 * match the state "is the filp on a fasync list".
 *
 */
int fasync_remove_entry(struct file *filp, struct fasync_struct **fapp)
{
    struct fasync_struct *fa, **fp;
    int result = 0;

    spin_lock(&filp->f_lock);
    spin_lock(&fasync_lock);
    for (fp = fapp; (fa = *fp) != NULL; fp = &fa->fa_next) {
        if (fa->fa_file != filp)
            continue;

        spin_lock_irq(&fa->fa_lock);
        fa->fa_file = NULL;
        spin_unlock_irq(&fa->fa_lock);

        *fp = fa->fa_next;
        call_rcu(&fa->fa_rcu, fasync_free_rcu);
        filp->f_flags &= ~FASYNC;
        result = 1;
        break;
    }
    spin_unlock(&fasync_lock);
    spin_unlock(&filp->f_lock);
    return result;
}

struct fasync_struct *fasync_alloc(void)
{
    return kmem_cache_alloc(fasync_cache, GFP_KERNEL);
}

/*
 * NOTE! This can be used only for unused fasync entries:
 * entries that actually got inserted on the fasync list
 * need to be released by rcu - see fasync_remove_entry.
 */
void fasync_free(struct fasync_struct *new)
{
    kmem_cache_free(fasync_cache, new);
}

/*
 * Insert a new entry into the fasync list.  Return the pointer to the
 * old one if we didn't use the new one.
 *
 * NOTE! It is very important that the FASYNC flag always
 * match the state "is the filp on a fasync list".
 */
struct fasync_struct *fasync_insert_entry(int fd, struct file *filp, struct fasync_struct **fapp, struct fasync_struct *new)
{
        struct fasync_struct *fa, **fp;

    spin_lock(&filp->f_lock);
    spin_lock(&fasync_lock);
    for (fp = fapp; (fa = *fp) != NULL; fp = &fa->fa_next) {
        if (fa->fa_file != filp)
            continue;

        spin_lock_irq(&fa->fa_lock);
        fa->fa_fd = fd;
        spin_unlock_irq(&fa->fa_lock);
        goto out;
    }

    spin_lock_init(&new->fa_lock);
    new->magic = FASYNC_MAGIC;
    new->fa_file = filp;
    new->fa_fd = fd;
    new->fa_next = *fapp;
    rcu_assign_pointer(*fapp, new);
    filp->f_flags |= FASYNC;

out:
    spin_unlock(&fasync_lock);
    spin_unlock(&filp->f_lock);
    return fa;
}

/*
 * Add a fasync entry. Return negative on error, positive if
 * added, and zero if did nothing but change an existing one.
 */
static int fasync_add_entry(int fd, struct file *filp, struct fasync_struct **fapp)
{
    struct fasync_struct *new;

    new = fasync_alloc();
    if (!new)
        return -ENOMEM;

    /*
     * fasync_insert_entry() returns the old (update) entry if
     * it existed.
     *
     * So free the (unused) new entry and return 0 to let the
     * caller know that we didn't add any new fasync entries.
     */
    if (fasync_insert_entry(fd, filp, fapp, new)) {
        fasync_free(new);
        return 0;
    }

    return 1;
}

/*
 * fasync_helper() is used by almost all character device drivers
 * to set up the fasync queue, and for regular files by the file
 * lease code. It returns negative on error, 0 if it did no changes
 * and positive if it added/deleted the entry.
 */
int fasync_helper(int fd, struct file * filp, int on, struct fasync_struct **fapp)
{
    if (!on)
        return fasync_remove_entry(filp, fapp);
    return fasync_add_entry(fd, filp, fapp);
}

EXPORT_SYMBOL(fasync_helper);

/*
 * rcu_read_lock() is held
 */
static void kill_fasync_rcu(struct fasync_struct *fa, int sig, int band)
{
    while (fa) {
        struct fown_struct *fown;
        unsigned long flags;

        if (fa->magic != FASYNC_MAGIC) {
            printk(KERN_ERR "kill_fasync: bad magic number in "
                   "fasync_struct!\n");
            return;
        }
        spin_lock_irqsave(&fa->fa_lock, flags);
        if (fa->fa_file) {
            fown = &fa->fa_file->f_owner;
            /* Don't send SIGURG to processes which have not set a
               queued signum: SIGURG has its own default signalling
               mechanism. */
            if (!(sig == SIGURG && fown->signum == 0))
                send_sigio(fown, fa->fa_fd, band);
        }
        spin_unlock_irqrestore(&fa->fa_lock, flags);
        fa = rcu_dereference(fa->fa_next);
    }
}

void kill_fasync(struct fasync_struct **fp, int sig, int band)
{
    /* First a quick test without locking: usually
     * the list is empty.
     */
    if (*fp) {
        rcu_read_lock();
        kill_fasync_rcu(rcu_dereference(*fp), sig, band);
        rcu_read_unlock();
    }
}
EXPORT_SYMBOL(kill_fasync);

static int __init fcntl_init(void)
{
    /*
     * Please add new bits here to ensure allocation uniqueness.
     * Exceptions: O_NONBLOCK is a two bit define on parisc; O_NDELAY
     * is defined as O_NONBLOCK on some platforms and not on others.
     */
    BUILD_BUG_ON(19 - 1 /* for O_RDONLY being 0 */ != HWEIGHT32(
        O_RDONLY    | O_WRONLY  | O_RDWR    |
        O_CREAT     | O_EXCL    | O_NOCTTY  |
        O_TRUNC     | O_APPEND  | /* O_NONBLOCK | */
        __O_SYNC    | O_DSYNC   | FASYNC    |
        O_DIRECT    | O_LARGEFILE   | O_DIRECTORY   |
        O_NOFOLLOW  | O_NOATIME | O_CLOEXEC |
        __FMODE_EXEC    | O_PATH
        ));

    fasync_cache = kmem_cache_create("fasync_cache",
        sizeof(struct fasync_struct), 0, SLAB_PANIC, NULL);
    return 0;
}

module_init(fcntl_init)