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authorDongli Zhang <dongli.zhang@oracle.com>2019-03-18 20:23:17 +0800
committerJens Axboe <axboe@kernel.dk>2019-03-18 08:20:53 -0600
commitf7c8a4120eedf24c36090b7542b179ff7a649219 (patch)
treec788565eb16ff83ad2bd624a4487e4f8aeabfa9f /drivers/block/loop.c
parent684b73245cd4d2608f4f2214f6bff02ba6ceca5f (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/loop.c')
-rw-r--r--drivers/block/loop.c2
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;