On Mon, Apr 17 2023 at 1:08P -0400, Zheng Zhang <zheng.zh...@email.ucr.edu> wrote:
> Alasdir, Mike, and to whom it may concern: > > Hello! We have found a bug in the Linux kernel version 6.2.0 by syzkaller > with our own templates. The bug causes a possible recursive locking > scenario, resulting in a deadlock. > The key trace is as follows (the complete trace is in the attached report > file): > > 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 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 > > Attached is the report, log, and reproducers generated by syzkaller > Please let me know if there is any additional information that I can > provide to help debug this issue. > Thanks! Thanks for the report, I've staged this fix: From: Mike Snitzer <snit...@kernel.org> 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: sta...@vger.kernel.org Reported-by: Zheng Zhang <zheng.zh...@email.ucr.edu> Signed-off-by: Mike Snitzer <snit...@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 50a1259294d1..7d5c9c582ed2 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); -- 2.40.0 -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel
