From 351050ecd6523374b370341cc29fe61e2201556b Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 30 Aug 2017 09:29:31 -0700 Subject: [PATCH] kcm: do not attach PF_KCM sockets to avoid deadlock syzkaller had no problem to trigger a deadlock, attaching a KCM socket to another one (or itself). (original syzkaller report was a very confusing lockdep splat during a sendmsg()) It seems KCM claims to only support TCP, but no enforcement is done, so we might need to add additional checks. Fixes: ab7ac4eb9832 ("kcm: Kernel Connection Multiplexor module") Signed-off-by: Eric Dumazet Reported-by: Dmitry Vyukov Acked-by: Tom Herbert Signed-off-by: David S. Miller --- net/kcm/kcmsock.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c index da49191f7ad0..4abf6287d7e1 100644 --- a/net/kcm/kcmsock.c +++ b/net/kcm/kcmsock.c @@ -1383,6 +1383,10 @@ static int kcm_attach(struct socket *sock, struct socket *csock, if (!csk) return -EINVAL; + /* We must prevent loops or risk deadlock ! */ + if (csk->sk_family == PF_KCM) + return -EOPNOTSUPP; + psock = kmem_cache_zalloc(kcm_psockp, GFP_KERNEL); if (!psock) return -ENOMEM;