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On Mon, Apr 09, 2018 at 04:53:22PM +0200, Pablo Neira Ayuso wrote:
> On Mon, Apr 09, 2018 at 10:20:18AM +0300, Simon Horman wrote:
> > 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?
Great, thanks!
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