kcm: do not attach PF_KCM sockets to avoid deadlock

[ Upstream commit 351050ecd6 ]

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: ab7ac4eb98 ("kcm: Kernel Connection Multiplexor module")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Tom Herbert <tom@quantonium.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Eric Dumazet 6 years ago committed by Greg Kroah-Hartman
parent 8c623e5d03
commit af33da0ed9

@ -1381,6 +1381,10 @@ 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)
psock = kmem_cache_zalloc(kcm_psockp, GFP_KERNEL);
if (!psock)
return -ENOMEM;