Re: [PATCH net] ipvs: fix rtnl_lock lockups caused by start_sync_thread

To: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Subject: Re: [PATCH net] ipvs: fix rtnl_lock lockups caused by start_sync_thread
Cc: Julian Anastasov <ja@xxxxxx>, lvs-devel@xxxxxxxxxxxxxxx, netfilter-devel@xxxxxxxxxxxxxxx
From: Simon Horman <horms@xxxxxxxxxxxx>
Date: Mon, 9 Apr 2018 10:20:18 +0300
On Sat, Apr 07, 2018 at 03:50:47PM +0300, Julian Anastasov wrote:
> syzkaller reports for wrong rtnl_lock usage in sync code [1] and [2]
> We have 2 problems in start_sync_thread if error path is
> taken, eg. on memory allocation error or failure to configure
> sockets for mcast group or addr/port binding:
> 1. recursive locking: holding rtnl_lock while calling sock_release
> which in turn calls again rtnl_lock in ip_mc_drop_socket to leave
> the mcast group, as noticed by Florian Westphal. Additionally,
> sock_release can not be called while holding sync_mutex (ABBA
> deadlock).
> 2. task hung: holding rtnl_lock while calling kthread_stop to
> stop the running kthreads. As the kthreads do the same to leave
> the mcast group (sock_release -> ip_mc_drop_socket -> rtnl_lock)
> they hang.
> Fix the problems by calling rtnl_unlock early in the error path,
> now sock_release is called after unlocking both mutexes.
> Problem 3 (task hung reported by syzkaller [2]) is variant of
> problem 2: use _trylock to prevent one user to call rtnl_lock and
> then while waiting for sync_mutex to block kthreads that execute
> sock_release when they are stopped by stop_sync_thread.


> Reported-and-tested-by: syzbot+a46d6abf9d56b1365a72@xxxxxxxxxxxxxxxxxxxxxxxxx
> Reported-and-tested-by: syzbot+5fe074c01b2032ce9618@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: e0b26cc997d5 ("ipvs: call rtnl_lock early")
> Signed-off-by: Julian Anastasov <ja@xxxxxx>

Signed-off-by: Simon Horman <horms@xxxxxxxxxxxx>

Pablo, could you take this directly into nf and then onwards to net?


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