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kcm: do not attach PF_KCM sockets to avoid deadlock

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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 <[email protected]>
Reported-by: Dmitry Vyukov <[email protected]>
Acked-by: Tom Herbert <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
This commit is contained in:
Eric Dumazet 2017-08-30 09:29:31 -07:00 • committed by David S. Miller
commit 351050ecd6
1 changed files with 4 additions and 0 deletions
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4
net/kcm/kcmsock.c
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@ -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;