[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <20190326042703.417780224@linuxfoundation.org>
Date: Tue, 26 Mar 2019 15:30:33 +0900
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org,
syzbot+9bdc1adc1c55e7fe765b@...kaller.appspotmail.com,
Dongli Zhang <dongli.zhang@...cle.com>,
Jan Kara <jack@...e.cz>, Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 5.0 46/52] loop: access lo_backing_file only when the loop device is Lo_bound
5.0-stable review patch. If anyone has any objections, please let me know.
------------------
From: Dongli Zhang <dongli.zhang@...cle.com>
commit f7c8a4120eedf24c36090b7542b179ff7a649219 upstream.
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@...kaller.appspotmail.com
Signed-off-by: Dongli Zhang <dongli.zhang@...cle.com>
Reviewed-by: Jan Kara <jack@...e.cz>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
drivers/block/loop.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -656,7 +656,7 @@ static int loop_validate_file(struct fil
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;
Powered by blists - more mailing lists