[SRU][Focal][PATCH 1/1] dm ioctl: fix nested locking in table_clear() to remove deadlock concern

Yuxuan Luo yuxuan.luo at canonical.com
Fri Jul 28 19:40:16 UTC 2023


From: Mike Snitzer <snitzer at kernel.org>

syzkaller found the following problematic rwsem locking (with write
lock already held):

 down_read+0x9d/0x450 kernel/locking/rwsem.c:1509
 dm_get_inactive_table+0x2b/0xc0 drivers/md/dm-ioctl.c:773
 __dev_status+0x4fd/0x7c0 drivers/md/dm-ioctl.c:844
 table_clear+0x197/0x280 drivers/md/dm-ioctl.c:1537

In table_clear, it first acquires a write lock
https://elixir.bootlin.com/linux/v6.2/source/drivers/md/dm-ioctl.c#L1520
down_write(&_hash_lock);

Then before the lock is released at L1539, there is a path shown above:
table_clear -> __dev_status -> dm_get_inactive_table ->  down_read
https://elixir.bootlin.com/linux/v6.2/source/drivers/md/dm-ioctl.c#L773
down_read(&_hash_lock);

It tries to acquire the same read lock again, resulting in the deadlock
problem.

Fix this by moving table_clear()'s __dev_status() call to after its
up_write(&_hash_lock);

Cc: stable at vger.kernel.org
Reported-by: Zheng Zhang <zheng.zhang at email.ucr.edu>
Signed-off-by: Mike Snitzer <snitzer at kernel.org>
(cherry picked from commit 3d32aaa7e66d5c1479a3c31d6c2c5d45dd0d3b89)
CVE-2023-2269
Signed-off-by: Yuxuan Luo <yuxuan.luo at canonical.com>
---
 drivers/md/dm-ioctl.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index bcb282f110531..477e616a21c74 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1435,11 +1435,12 @@ static int table_clear(struct file *filp, struct dm_ioctl *param, size_t param_s
 		hc->new_map = NULL;
 	}
 
-	param->flags &= ~DM_INACTIVE_PRESENT_FLAG;
-
-	__dev_status(hc->md, param);
 	md = hc->md;
 	up_write(&_hash_lock);
+
+	param->flags &= ~DM_INACTIVE_PRESENT_FLAG;
+	__dev_status(md, param);
+
 	if (old_map) {
 		dm_sync_table(md);
 		dm_table_destroy(old_map);
-- 
2.34.1




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