| Message ID | 1552911797-20455-1-git-send-email-dongli.zhang@oracle.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/1] loop: access lo_backing_file only when the loop device is Lo_bound | expand |
On 3/18/19 6:23 AM, Dongli Zhang wrote: > 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. Thanks, applied.
diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 1e6edd5..bf1c61c 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;
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> --- drivers/block/loop.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)