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block/loop: Use global lock for ioctl() operation. 

commit 310ca162d7 upstream.

syzbot is reporting NULL pointer dereference [1] which is caused by
race condition between ioctl(loop_fd, LOOP_CLR_FD, 0) versus
ioctl(other_loop_fd, LOOP_SET_FD, loop_fd) due to traversing other
loop devices at loop_validate_file() without holding corresponding
lo->lo_ctl_mutex locks.

Since ioctl() request on loop devices is not frequent operation, we don't
need fine grained locking. Let's use global lock in order to allow safe
traversal at loop_validate_file().

Note that syzbot is also reporting circular locking dependency between
bdev->bd_mutex and lo->lo_ctl_mutex [2] which is caused by calling
blkdev_reread_part() with lock held. This patch does not address it.

[1] https://syzkaller.appspot.com/bug?id=f3cfe26e785d85f9ee259f385515291d21bd80a3
[2] https://syzkaller.appspot.com/bug?id=bf154052f0eea4bc7712499e4569505907d15889

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+bf89c128e05dd6c62523@syzkaller.appspotmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Tetsuo Handa 2018-11-08 14:01:02 +01:00 committed by Greg Kroah-Hartman
parent 02862eb917
commit 3ae3d167f5
2 changed files with 21 additions and 22 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

42
drivers/block/loop.c
View File

@ -82,6 +82,7 @@
static DEFINE_IDR(loop_index_idr);
static DEFINE_MUTEX(loop_index_mutex);
static DEFINE_MUTEX(loop_ctl_mutex);
static int max_part;
static int part_shift;
@ -1033,7 +1034,7 @@ static int loop_clr_fd(struct loop_device *lo)
*/
if (atomic_read(&lo->lo_refcnt) > 1) {
lo->lo_flags |= LO_FLAGS_AUTOCLEAR;
mutex_unlock(&lo->lo_ctl_mutex);
mutex_unlock(&loop_ctl_mutex);
return 0;
}
@ -1082,12 +1083,12 @@ static int loop_clr_fd(struct loop_device *lo)
if (!part_shift)
lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;
loop_unprepare_queue(lo);
mutex_unlock(&lo->lo_ctl_mutex);
mutex_unlock(&loop_ctl_mutex);
/*
* Need not hold lo_ctl_mutex to fput backing file.
* Calling fput holding lo_ctl_mutex triggers a circular
* Need not hold loop_ctl_mutex to fput backing file.
* Calling fput holding loop_ctl_mutex triggers a circular
* lock dependency possibility warning as fput can take
* bd_mutex which is usually taken before lo_ctl_mutex.
* bd_mutex which is usually taken before loop_ctl_mutex.
*/
fput(filp);
return 0;
@ -1350,7 +1351,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
struct loop_device *lo = bdev->bd_disk->private_data;
int err;
mutex_lock_nested(&lo->lo_ctl_mutex, 1);
mutex_lock_nested(&loop_ctl_mutex, 1);
switch (cmd) {
case LOOP_SET_FD:
err = loop_set_fd(lo, mode, bdev, arg);
@ -1359,7 +1360,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
err = loop_change_fd(lo, bdev, arg);
break;
case LOOP_CLR_FD:
/* loop_clr_fd would have unlocked lo_ctl_mutex on success */
/* loop_clr_fd would have unlocked loop_ctl_mutex on success */
err = loop_clr_fd(lo);
if (!err)
goto out_unlocked;
@ -1395,7 +1396,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
default:
err = lo->ioctl ? lo->ioctl(lo, cmd, arg) : -EINVAL;
}
mutex_unlock(&lo->lo_ctl_mutex);
mutex_unlock(&loop_ctl_mutex);
out_unlocked:
return err;
@ -1528,16 +1529,16 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode,
switch(cmd) {
case LOOP_SET_STATUS:
mutex_lock(&lo->lo_ctl_mutex);
mutex_lock(&loop_ctl_mutex);
err = loop_set_status_compat(
lo, (const struct compat_loop_info __user *) arg);
mutex_unlock(&lo->lo_ctl_mutex);
mutex_unlock(&loop_ctl_mutex);
break;
case LOOP_GET_STATUS:
mutex_lock(&lo->lo_ctl_mutex);
mutex_lock(&loop_ctl_mutex);
err = loop_get_status_compat(
lo, (struct compat_loop_info __user *) arg);
mutex_unlock(&lo->lo_ctl_mutex);
mutex_unlock(&loop_ctl_mutex);
break;
case LOOP_SET_CAPACITY:
case LOOP_CLR_FD:
@ -1581,7 +1582,7 @@ static void __lo_release(struct loop_device *lo)
if (atomic_dec_return(&lo->lo_refcnt))
return;
mutex_lock(&lo->lo_ctl_mutex);
mutex_lock(&loop_ctl_mutex);
if (lo->lo_flags & LO_FLAGS_AUTOCLEAR) {
/*
* In autoclear mode, stop the loop thread
@ -1598,7 +1599,7 @@ static void __lo_release(struct loop_device *lo)
loop_flush(lo);
}
mutex_unlock(&lo->lo_ctl_mutex);
mutex_unlock(&loop_ctl_mutex);
}
static void lo_release(struct gendisk *disk, fmode_t mode)
@ -1644,10 +1645,10 @@ static int unregister_transfer_cb(int id, void *ptr, void *data)
struct loop_device *lo = ptr;
struct loop_func_table *xfer = data;
mutex_lock(&lo->lo_ctl_mutex);
mutex_lock(&loop_ctl_mutex);
if (lo->lo_encryption == xfer)
loop_release_xfer(lo);
mutex_unlock(&lo->lo_ctl_mutex);
mutex_unlock(&loop_ctl_mutex);
return 0;
}
@ -1813,7 +1814,6 @@ static int loop_add(struct loop_device **l, int i)
if (!part_shift)
disk->flags |= GENHD_FL_NO_PART_SCAN;
disk->flags |= GENHD_FL_EXT_DEVT;
mutex_init(&lo->lo_ctl_mutex);
atomic_set(&lo->lo_refcnt, 0);
lo->lo_number = i;
spin_lock_init(&lo->lo_lock);
@ -1926,19 +1926,19 @@ static long loop_control_ioctl(struct file *file, unsigned int cmd,
ret = loop_lookup(&lo, parm);
if (ret < 0)
break;
mutex_lock(&lo->lo_ctl_mutex);
mutex_lock(&loop_ctl_mutex);
if (lo->lo_state != Lo_unbound) {
ret = -EBUSY;
mutex_unlock(&lo->lo_ctl_mutex);
mutex_unlock(&loop_ctl_mutex);
break;
}
if (atomic_read(&lo->lo_refcnt) > 0) {
ret = -EBUSY;
mutex_unlock(&lo->lo_ctl_mutex);
mutex_unlock(&loop_ctl_mutex);
break;
}
lo->lo_disk->private_data = NULL;
mutex_unlock(&lo->lo_ctl_mutex);
mutex_unlock(&loop_ctl_mutex);
idr_remove(&loop_index_idr, lo->lo_number);
loop_remove(lo);
break;

1
drivers/block/loop.h
View File

@ -55,7 +55,6 @@ struct loop_device {
spinlock_t lo_lock;
int lo_state;
struct mutex lo_ctl_mutex;
struct kthread_worker worker;
struct task_struct *worker_task;
bool use_dio;