4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Eric Dumazet <edumazet@xxxxxxxxxx>
[ Upstream commit 351050ecd6523374b370341cc29fe61e2201556b ]
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 <edumazet@xxxxxxxxxx>
Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Acked-by: Tom Herbert <tom@xxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/kcm/kcmsock.c | 4 ++++
1 file changed, 4 insertions(+)
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -1381,6 +1381,10 @@ static int kcm_attach(struct socket *soc
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;