dm ioctl: fix nested locking in table_clear() to remove deadlock concern

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@vger.kernel.org
Reported-by: Zheng Zhang <zheng.zhang@email.ucr.edu>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 50a1259..7d5c9c5 100644 (file)
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1556,11 +1556,12 @@ static int table_clear(struct file *filp, struct dm_ioctl *param, size_t param_s
                has_new_map = true;
        }
 
-       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);