diff options
| author | Jan Kara <jack@suse.cz> | 2019-05-16 16:01:27 +0200 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2019-05-27 07:34:04 -0600 |
| commit | 33ec3e53e7b1869d7851e59e126bdb0fe0bd1982 (patch) | |
| tree | c6f6599a2a13a0bf456854d291a942cc5297e090 /drivers/block/loop.c | |
| parent | a278682dad37fd2f8d2f30d8e84e376a856ab472 (diff) | |
| download | linux-33ec3e53e7b1869d7851e59e126bdb0fe0bd1982.tar.gz | |
loop: Don't change loop device under exclusive opener
Loop module allows calling LOOP_SET_FD while there are other openers of
the loop device. Even exclusive ones. This can lead to weird
consequences such as kernel deadlocks like:
mount_bdev() lo_ioctl()
udf_fill_super()
udf_load_vrs()
sb_set_blocksize() - sets desired block size B
udf_tread()
sb_bread()
__bread_gfp(bdev, block, B)
loop_set_fd()
set_blocksize()
- now __getblk_slow() indefinitely loops because B != bdev
block size
Fix the problem by disallowing LOOP_SET_FD ioctl when there are
exclusive openers of a loop device.
[Deliberately chosen not to CC stable as a user with priviledges to
trigger this race has other means of taking the system down and this
has a potential of breaking some weird userspace setup]
Reported-and-tested-by: syzbot+10007d66ca02b08f0e60@syzkaller.appspotmail.com
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'drivers/block/loop.c')
| -rw-r--r-- | drivers/block/loop.c | 18 |
1 files changed, 17 insertions, 1 deletions
diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 102d795758959f..f11b7dc16e9d40 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -945,9 +945,20 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode, if (!file) goto out; + /* + * If we don't hold exclusive handle for the device, upgrade to it + * here to avoid changing device under exclusive owner. + */ + if (!(mode & FMODE_EXCL)) { + bdgrab(bdev); + error = blkdev_get(bdev, mode | FMODE_EXCL, loop_set_fd); + if (error) + goto out_putf; + } + error = mutex_lock_killable(&loop_ctl_mutex); if (error) - goto out_putf; + goto out_bdev; error = -EBUSY; if (lo->lo_state != Lo_unbound) @@ -1012,10 +1023,15 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode, mutex_unlock(&loop_ctl_mutex); if (partscan) loop_reread_partitions(lo, bdev); + if (!(mode & FMODE_EXCL)) + blkdev_put(bdev, mode | FMODE_EXCL); return 0; out_unlock: mutex_unlock(&loop_ctl_mutex); +out_bdev: + if (!(mode & FMODE_EXCL)) + blkdev_put(bdev, mode | FMODE_EXCL); out_putf: fput(file); out: |