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From 3d32aaa7e66d5c1479a3c31d6c2c5d45dd0d3b89 Mon Sep 17 00:00:00 2001
From: Mike Snitzer <snitzer@kernel.org>
Date: Mon, 17 Apr 2023 11:59:56 -0400
Subject: [PATCH] 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>
---
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 50a1259294d141..7d5c9c582ed2d6 100644
--- 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);
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