diff options
| author | Dongli Zhang <dongli.zhang@oracle.com> | 2019-03-18 20:23:17 +0800 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2019-03-18 08:20:53 -0600 |
| commit | f7c8a4120eedf24c36090b7542b179ff7a649219 (patch) | |
| tree | c788565eb16ff83ad2bd624a4487e4f8aeabfa9f /drivers/block | |
| parent | 684b73245cd4d2608f4f2214f6bff02ba6ceca5f (diff) | |
loop: access lo_backing_file only when the loop device is Lo_bound
Commit 758a58d0bc67 ("loop: set GENHD_FL_NO_PART_SCAN after
blkdev_reread_part()") separates "lo->lo_backing_file = NULL" and
"lo->lo_state = Lo_unbound" into different critical regions protected by
loop_ctl_mutex.
However, there is below race that the NULL lo->lo_backing_file would be
accessed when the backend of a loop is another loop device, e.g., loop0's
backend is a file, while loop1's backend is loop0.
loop0's backend is file loop1's backend is loop0
__loop_clr_fd()
mutex_lock(&loop_ctl_mutex);
lo->lo_backing_file = NULL; --> set to NULL
mutex_unlock(&loop_ctl_mutex);
loop_set_fd()
mutex_lock_killable(&loop_ctl_mutex);
loop_validate_file()
f = l->lo_backing_file; --> NULL
access if loop0 is not Lo_unbound
mutex_lock(&loop_ctl_mutex);
lo->lo_state = Lo_unbound;
mutex_unlock(&loop_ctl_mutex);
lo->lo_backing_file should be accessed only when the loop device is
Lo_bound.
In fact, the problem has been introduced already in commit 7ccd0791d985
("loop: Push loop_ctl_mutex down into loop_clr_fd()") after which
loop_validate_file() could see devices in Lo_rundown state with which it
did not count. It was harmless at that point but still.
Fixes: 7ccd0791d985 ("loop: Push loop_ctl_mutex down into loop_clr_fd()")
Reported-by: syzbot+9bdc1adc1c55e7fe765b@syzkaller.appspotmail.com
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'drivers/block')
| -rw-r--r-- | drivers/block/loop.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 1e6edd568214..bf1c61cab8eb 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -656,7 +656,7 @@ static int loop_validate_file(struct file *file, struct block_device *bdev) return -EBADF; l = f->f_mapping->host->i_bdev->bd_disk->private_data; - if (l->lo_state == Lo_unbound) { + if (l->lo_state != Lo_bound) { return -EINVAL; } f = l->lo_backing_file; |