A potential bug in inotify_user.c

[deliverable/linux.git] / fs / inotify_user.c

/*
 * fs/inotify_user.c - inotify support for userspace
 *
 * Authors:
 *      John McCutchan  <ttb@tentacle.dhs.org>
 *      Robert Love     <rml@novell.com>
 *
 * Copyright (C) 2005 John McCutchan
 * Copyright 2006 Hewlett-Packard Development Company, L.P.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2, or (at your option) any
 * later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 */

#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/poll.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/inotify.h>
#include <linux/syscalls.h>
#include <linux/magic.h>

#include <asm/ioctls.h>

static struct kmem_cache *watch_cachep __read_mostly;
static struct kmem_cache *event_cachep __read_mostly;

static struct vfsmount *inotify_mnt __read_mostly;

/* these are configurable via /proc/sys/fs/inotify/ */
int inotify_max_user_instances __read_mostly;
int inotify_max_user_watches __read_mostly;
int inotify_max_queued_events __read_mostly;

/*
 * Lock ordering:
 *
 * inotify_dev->up_mutex (ensures we don't re-add the same watch)
 *      inode->inotify_mutex (protects inode's watch list)
 *              inotify_handle->mutex (protects inotify_handle's watch list)
 *                      inotify_dev->ev_mutex (protects device's event queue)
 */

/*
 * Lifetimes of the main data structures:
 *
 * inotify_device: Lifetime is managed by reference count, from
 * sys_inotify_init() until release.  Additional references can bump the count
 * via get_inotify_dev() and drop the count via put_inotify_dev().
 *
 * inotify_user_watch: Lifetime is from create_watch() to the receipt of an
 * IN_IGNORED event from inotify, or when using IN_ONESHOT, to receipt of the
 * first event, or to inotify_destroy().
 */

/*
 * struct inotify_device - represents an inotify instance
 *
 * This structure is protected by the mutex 'mutex'.
 */
struct inotify_device {
        wait_queue_head_t       wq;             /* wait queue for i/o */
        struct mutex            ev_mutex;       /* protects event queue */
        struct mutex            up_mutex;       /* synchronizes watch updates */
        struct list_head        events;         /* list of queued events */
        atomic_t                count;          /* reference count */
        struct user_struct      *user;          /* user who opened this dev */
        struct inotify_handle   *ih;            /* inotify handle */
        unsigned int            queue_size;     /* size of the queue (bytes) */
        unsigned int            event_count;    /* number of pending events */
        unsigned int            max_events;     /* maximum number of events */
};

/*
 * struct inotify_kernel_event - An inotify event, originating from a watch and
 * queued for user-space.  A list of these is attached to each instance of the
 * device.  In read(), this list is walked and all events that can fit in the
 * buffer are returned.
 *
 * Protected by dev->ev_mutex of the device in which we are queued.
 */
struct inotify_kernel_event {
        struct inotify_event    event;  /* the user-space event */
        struct list_head        list;   /* entry in inotify_device's list */
        char                    *name;  /* filename, if any */
};

/*
 * struct inotify_user_watch - our version of an inotify_watch, we add
 * a reference to the associated inotify_device.
 */
struct inotify_user_watch {
        struct inotify_device   *dev;   /* associated device */
        struct inotify_watch    wdata;  /* inotify watch data */
};

#ifdef CONFIG_SYSCTL

#include <linux/sysctl.h>

static int zero;

ctl_table inotify_table[] = {
        {
                .ctl_name       = INOTIFY_MAX_USER_INSTANCES,
                .procname       = "max_user_instances",
                .data           = &inotify_max_user_instances,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = &proc_dointvec_minmax,
                .strategy       = &sysctl_intvec,
                .extra1         = &zero,
        },
        {
                .ctl_name       = INOTIFY_MAX_USER_WATCHES,
                .procname       = "max_user_watches",
                .data           = &inotify_max_user_watches,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = &proc_dointvec_minmax,
                .strategy       = &sysctl_intvec,
                .extra1         = &zero,
        },
        {
                .ctl_name       = INOTIFY_MAX_QUEUED_EVENTS,
                .procname       = "max_queued_events",
                .data           = &inotify_max_queued_events,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = &proc_dointvec_minmax,
                .strategy       = &sysctl_intvec,
                .extra1         = &zero
        },
        { .ctl_name = 0 }
};
#endif /* CONFIG_SYSCTL */

static inline void get_inotify_dev(struct inotify_device *dev)
{
        atomic_inc(&dev->count);
}

static inline void put_inotify_dev(struct inotify_device *dev)
{
        if (atomic_dec_and_test(&dev->count)) {
                atomic_dec(&dev->user->inotify_devs);
                free_uid(dev->user);
                kfree(dev);
        }
}

/*
 * free_inotify_user_watch - cleans up the watch and its references
 */
static void free_inotify_user_watch(struct inotify_watch *w)
{
        struct inotify_user_watch *watch;
        struct inotify_device *dev;

        watch = container_of(w, struct inotify_user_watch, wdata);
        dev = watch->dev;

        atomic_dec(&dev->user->inotify_watches);
        put_inotify_dev(dev);
        kmem_cache_free(watch_cachep, watch);
}

/*
 * kernel_event - create a new kernel event with the given parameters
 *
 * This function can sleep.
 */
static struct inotify_kernel_event * kernel_event(s32 wd, u32 mask, u32 cookie,
                                                  const char *name)
{
        struct inotify_kernel_event *kevent;

        kevent = kmem_cache_alloc(event_cachep, GFP_NOFS);
        if (unlikely(!kevent))
                return NULL;

        /* we hand this out to user-space, so zero it just in case */
        memset(&kevent->event, 0, sizeof(struct inotify_event));

        kevent->event.wd = wd;
        kevent->event.mask = mask;
        kevent->event.cookie = cookie;

        INIT_LIST_HEAD(&kevent->list);

        if (name) {
                size_t len, rem, event_size = sizeof(struct inotify_event);

                /*
                 * We need to pad the filename so as to properly align an
                 * array of inotify_event structures.  Because the structure is
                 * small and the common case is a small filename, we just round
                 * up to the next multiple of the structure's sizeof.  This is
                 * simple and safe for all architectures.
                 */
                len = strlen(name) + 1;
                rem = event_size - len;
                if (len > event_size) {
                        rem = event_size - (len % event_size);
                        if (len % event_size == 0)
                                rem = 0;
                }

                kevent->name = kmalloc(len + rem, GFP_KERNEL);
                if (unlikely(!kevent->name)) {
                        kmem_cache_free(event_cachep, kevent);
                        return NULL;
                }
                memcpy(kevent->name, name, len);
                if (rem)
                        memset(kevent->name + len, 0, rem);
                kevent->event.len = len + rem;
        } else {
                kevent->event.len = 0;
                kevent->name = NULL;
        }

        return kevent;
}

/*
 * inotify_dev_get_event - return the next event in the given dev's queue
 *
 * Caller must hold dev->ev_mutex.
 */
static inline struct inotify_kernel_event *
inotify_dev_get_event(struct inotify_device *dev)
{
        return list_entry(dev->events.next, struct inotify_kernel_event, list);
}

/*
 * inotify_dev_get_last_event - return the last event in the given dev's queue
 *
 * Caller must hold dev->ev_mutex.
 */
static inline struct inotify_kernel_event *
inotify_dev_get_last_event(struct inotify_device *dev)
{
        if (list_empty(&dev->events))
                return NULL;
        return list_entry(dev->events.prev, struct inotify_kernel_event, list);
}

/*
 * inotify_dev_queue_event - event handler registered with core inotify, adds
 * a new event to the given device
 *
 * Can sleep (calls kernel_event()).
 */
static void inotify_dev_queue_event(struct inotify_watch *w, u32 wd, u32 mask,
                                    u32 cookie, const char *name,
                                    struct inode *ignored)
{
        struct inotify_user_watch *watch;
        struct inotify_device *dev;
        struct inotify_kernel_event *kevent, *last;

        watch = container_of(w, struct inotify_user_watch, wdata);
        dev = watch->dev;

        mutex_lock(&dev->ev_mutex);

        /* we can safely put the watch as we don't reference it while
         * generating the event
         */
        if (mask & IN_IGNORED || mask & IN_ONESHOT)
                put_inotify_watch(w); /* final put */

        /* coalescing: drop this event if it is a dupe of the previous */
        last = inotify_dev_get_last_event(dev);
        if (last && last->event.mask == mask && last->event.wd == wd &&
                        last->event.cookie == cookie) {
                const char *lastname = last->name;

                if (!name && !lastname)
                        goto out;
                if (name && lastname && !strcmp(lastname, name))
                        goto out;
        }

        /* the queue overflowed and we already sent the Q_OVERFLOW event */
        if (unlikely(dev->event_count > dev->max_events))
                goto out;

        /* if the queue overflows, we need to notify user space */
        if (unlikely(dev->event_count == dev->max_events))
                kevent = kernel_event(-1, IN_Q_OVERFLOW, cookie, NULL);
        else
                kevent = kernel_event(wd, mask, cookie, name);

        if (unlikely(!kevent))
                goto out;

        /* queue the event and wake up anyone waiting */
        dev->event_count++;
        dev->queue_size += sizeof(struct inotify_event) + kevent->event.len;
        list_add_tail(&kevent->list, &dev->events);
        wake_up_interruptible(&dev->wq);

out:
        mutex_unlock(&dev->ev_mutex);
}

/*
 * remove_kevent - cleans up and ultimately frees the given kevent
 *
 * Caller must hold dev->ev_mutex.
 */
static void remove_kevent(struct inotify_device *dev,
                          struct inotify_kernel_event *kevent)
{
        list_del(&kevent->list);

        dev->event_count--;
        dev->queue_size -= sizeof(struct inotify_event) + kevent->event.len;

        kfree(kevent->name);
        kmem_cache_free(event_cachep, kevent);
}

/*
 * inotify_dev_event_dequeue - destroy an event on the given device
 *
 * Caller must hold dev->ev_mutex.
 */
static void inotify_dev_event_dequeue(struct inotify_device *dev)
{
        if (!list_empty(&dev->events)) {
                struct inotify_kernel_event *kevent;
                kevent = inotify_dev_get_event(dev);
                remove_kevent(dev, kevent);
        }
}

/*
 * find_inode - resolve a user-given path to a specific inode and return a nd
 */
static int find_inode(const char __user *dirname, struct nameidata *nd,
                      unsigned flags)
{
        int error;

        error = __user_walk(dirname, flags, nd);
        if (error)
                return error;
        /* you can only watch an inode if you have read permissions on it */
        error = vfs_permission(nd, MAY_READ);
        if (error)
                path_release(nd);
        return error;
}

/*
 * create_watch - creates a watch on the given device.
 *
 * Callers must hold dev->up_mutex.
 */
static int create_watch(struct inotify_device *dev, struct inode *inode,
                        u32 mask)
{
        struct inotify_user_watch *watch;
        int ret;

        if (atomic_read(&dev->user->inotify_watches) >=
                        inotify_max_user_watches)
                return -ENOSPC;

        watch = kmem_cache_alloc(watch_cachep, GFP_KERNEL);
        if (unlikely(!watch))
                return -ENOMEM;

        /* save a reference to device and bump the count to make it official */
        get_inotify_dev(dev);
        watch->dev = dev;

        atomic_inc(&dev->user->inotify_watches);

        inotify_init_watch(&watch->wdata);
        ret = inotify_add_watch(dev->ih, &watch->wdata, inode, mask);
        if (ret < 0)
                free_inotify_user_watch(&watch->wdata);

        return ret;
}

/* Device Interface */

static unsigned int inotify_poll(struct file *file, poll_table *wait)
{
        struct inotify_device *dev = file->private_data;
        int ret = 0;

        poll_wait(file, &dev->wq, wait);
        mutex_lock(&dev->ev_mutex);
        if (!list_empty(&dev->events))
                ret = POLLIN | POLLRDNORM;
        mutex_unlock(&dev->ev_mutex);

        return ret;
}

static ssize_t inotify_read(struct file *file, char __user *buf,
                            size_t count, loff_t *pos)
{
        size_t event_size = sizeof (struct inotify_event);
        struct inotify_device *dev;
        char __user *start;
        int ret;
        DEFINE_WAIT(wait);

        start = buf;
        dev = file->private_data;

        while (1) {
                int events;

                prepare_to_wait(&dev->wq, &wait, TASK_INTERRUPTIBLE);

                mutex_lock(&dev->ev_mutex);
                events = !list_empty(&dev->events);
                mutex_unlock(&dev->ev_mutex);
                if (events) {
                        ret = 0;
                        break;
                }

                if (file->f_flags & O_NONBLOCK) {
                        ret = -EAGAIN;
                        break;
                }

                if (signal_pending(current)) {
                        ret = -EINTR;
                        break;
                }

                schedule();
        }

        finish_wait(&dev->wq, &wait);
        if (ret)
                return ret;

        mutex_lock(&dev->ev_mutex);
        while (1) {
                struct inotify_kernel_event *kevent;

                ret = buf - start;
                if (list_empty(&dev->events))
                        break;

                kevent = inotify_dev_get_event(dev);
                if (event_size + kevent->event.len > count) {
                        if (ret == 0 && count > 0) {
                                /*
                                 * could not get a single event because we
                                 * didn't have enough buffer space.
                                 */
                                ret = -EINVAL;
                        }
                        break;
                }

                if (copy_to_user(buf, &kevent->event, event_size)) {
                        ret = -EFAULT;
                        break;
                }
                buf += event_size;
                count -= event_size;

                if (kevent->name) {
                        if (copy_to_user(buf, kevent->name, kevent->event.len)){
                                ret = -EFAULT;
                                break;
                        }
                        buf += kevent->event.len;
                        count -= kevent->event.len;
                }

                remove_kevent(dev, kevent);
        }
        mutex_unlock(&dev->ev_mutex);

        return ret;
}

static int inotify_release(struct inode *ignored, struct file *file)
{
        struct inotify_device *dev = file->private_data;

        inotify_destroy(dev->ih);

        /* destroy all of the events on this device */
        mutex_lock(&dev->ev_mutex);
        while (!list_empty(&dev->events))
                inotify_dev_event_dequeue(dev);
        mutex_unlock(&dev->ev_mutex);

        /* free this device: the put matching the get in inotify_init() */
        put_inotify_dev(dev);

        return 0;
}

static long inotify_ioctl(struct file *file, unsigned int cmd,
                          unsigned long arg)
{
        struct inotify_device *dev;
        void __user *p;
        int ret = -ENOTTY;

        dev = file->private_data;
        p = (void __user *) arg;

        switch (cmd) {
        case FIONREAD:
                ret = put_user(dev->queue_size, (int __user *) p);
                break;
        }

        return ret;
}

static const struct file_operations inotify_fops = {
        .poll           = inotify_poll,
        .read           = inotify_read,
        .release        = inotify_release,
        .unlocked_ioctl = inotify_ioctl,
        .compat_ioctl   = inotify_ioctl,
};

static const struct inotify_operations inotify_user_ops = {
        .handle_event   = inotify_dev_queue_event,
        .destroy_watch  = free_inotify_user_watch,
};

asmlinkage long sys_inotify_init(void)
{
        struct inotify_device *dev;
        struct inotify_handle *ih;
        struct user_struct *user;
        struct file *filp;
        int fd, ret;

        fd = get_unused_fd();
        if (fd < 0)
                return fd;

        filp = get_empty_filp();
        if (!filp) {
                ret = -ENFILE;
                goto out_put_fd;
        }

        user = get_uid(current->user);
        if (unlikely(atomic_read(&user->inotify_devs) >=
                        inotify_max_user_instances)) {
                ret = -EMFILE;
                goto out_free_uid;
        }

        dev = kmalloc(sizeof(struct inotify_device), GFP_KERNEL);
        if (unlikely(!dev)) {
                ret = -ENOMEM;
                goto out_free_uid;
        }

        ih = inotify_init(&inotify_user_ops);
        if (unlikely(IS_ERR(ih))) {
                ret = PTR_ERR(ih);
                goto out_free_dev;
        }
        dev->ih = ih;

        filp->f_op = &inotify_fops;
        filp->f_path.mnt = mntget(inotify_mnt);
        filp->f_path.dentry = dget(inotify_mnt->mnt_root);
        filp->f_mapping = filp->f_path.dentry->d_inode->i_mapping;
        filp->f_mode = FMODE_READ;
        filp->f_flags = O_RDONLY;
        filp->private_data = dev;

        INIT_LIST_HEAD(&dev->events);
        init_waitqueue_head(&dev->wq);
        mutex_init(&dev->ev_mutex);
        mutex_init(&dev->up_mutex);
        dev->event_count = 0;
        dev->queue_size = 0;
        dev->max_events = inotify_max_queued_events;
        dev->user = user;
        atomic_set(&dev->count, 0);

        get_inotify_dev(dev);
        atomic_inc(&user->inotify_devs);
        fd_install(fd, filp);

        return fd;
out_free_dev:
        kfree(dev);
out_free_uid:
        free_uid(user);
        put_filp(filp);
out_put_fd:
        put_unused_fd(fd);
        return ret;
}

asmlinkage long sys_inotify_add_watch(int fd, const char __user *path, u32 mask)
{
        struct inode *inode;
        struct inotify_device *dev;
        struct nameidata nd;
        struct file *filp;
        int ret, fput_needed;
        unsigned flags = 0;

        filp = fget_light(fd, &fput_needed);
        if (unlikely(!filp))
                return -EBADF;

        /* verify that this is indeed an inotify instance */
        if (unlikely(filp->f_op != &inotify_fops)) {
                ret = -EINVAL;
                goto fput_and_out;
        }

        if (!(mask & IN_DONT_FOLLOW))
                flags |= LOOKUP_FOLLOW;
        if (mask & IN_ONLYDIR)
                flags |= LOOKUP_DIRECTORY;

        ret = find_inode(path, &nd, flags);
        if (unlikely(ret))
                goto fput_and_out;

        /* inode held in place by reference to nd; dev by fget on fd */
        inode = nd.dentry->d_inode;
        dev = filp->private_data;

        mutex_lock(&dev->up_mutex);
        ret = inotify_find_update_watch(dev->ih, inode, mask);
        if (ret == -ENOENT)
                ret = create_watch(dev, inode, mask);
        mutex_unlock(&dev->up_mutex);

        path_release(&nd);
fput_and_out:
        fput_light(filp, fput_needed);
        return ret;
}

asmlinkage long sys_inotify_rm_watch(int fd, u32 wd)
{
        struct file *filp;
        struct inotify_device *dev;
        int ret, fput_needed;

        filp = fget_light(fd, &fput_needed);
        if (unlikely(!filp))
                return -EBADF;

        /* verify that this is indeed an inotify instance */
        if (unlikely(filp->f_op != &inotify_fops)) {
                ret = -EINVAL;
                goto out;
        }

        dev = filp->private_data;

        /* we free our watch data when we get IN_IGNORED */
        ret = inotify_rm_wd(dev->ih, wd);

out:
        fput_light(filp, fput_needed);
        return ret;
}

static int
inotify_get_sb(struct file_system_type *fs_type, int flags,
               const char *dev_name, void *data, struct vfsmount *mnt)
{
        return get_sb_pseudo(fs_type, "inotify", NULL,
                        INOTIFYFS_SUPER_MAGIC, mnt);
}

static struct file_system_type inotify_fs_type = {
    .name           = "inotifyfs",
    .get_sb         = inotify_get_sb,
    .kill_sb        = kill_anon_super,
};

/*
 * inotify_user_setup - Our initialization function.  Note that we cannnot return
 * error because we have compiled-in VFS hooks.  So an (unlikely) failure here
 * must result in panic().
 */
static int __init inotify_user_setup(void)
{
        int ret;

        ret = register_filesystem(&inotify_fs_type);
        if (unlikely(ret))
                panic("inotify: register_filesystem returned %d!\n", ret);

        inotify_mnt = kern_mount(&inotify_fs_type);
        if (IS_ERR(inotify_mnt))
                panic("inotify: kern_mount ret %ld!\n", PTR_ERR(inotify_mnt));

        inotify_max_queued_events = 16384;
        inotify_max_user_instances = 128;
        inotify_max_user_watches = 8192;

        watch_cachep = kmem_cache_create("inotify_watch_cache",
                                         sizeof(struct inotify_user_watch),
                                         0, SLAB_PANIC, NULL);
        event_cachep = kmem_cache_create("inotify_event_cache",
                                         sizeof(struct inotify_kernel_event),
                                         0, SLAB_PANIC, NULL);

        return 0;
}

module_init(inotify_user_setup);