[net] kcm: do not attach PF_KCM sockets to avoid deadlock

Message ID 1504110571.11498.120.camel@edumazet-glaptop3.roam.corp.google.com
State Accepted
Delegated to: David Miller
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Series
  • [net] kcm: do not attach PF_KCM sockets to avoid deadlock
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Commit Message

Eric Dumazet Aug. 30, 2017, 4:29 p.m.
From: Eric Dumazet <edumazet@google.com>

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@google.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
---
 net/kcm/kcmsock.c |    4 ++++
 1 file changed, 4 insertions(+)

Comments

Tom Herbert Aug. 30, 2017, 4:42 p.m. | #1
On Wed, Aug 30, 2017 at 9:29 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> From: Eric Dumazet <edumazet@google.com>
>
> 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@google.com>
> Reported-by: Dmitry Vyukov <dvyukov@google.com>

Acked-by: Tom Herbert <tom@quantonium.net>

> ---
>  net/kcm/kcmsock.c |    4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
> index 48e993b2dbcf1afae04968ed840e2e98c2cf6772..af4e76ac88ff0817398d1d7460a41f0cd5fe6f30 100644
> --- a/net/kcm/kcmsock.c
> +++ b/net/kcm/kcmsock.c
> @@ -1387,6 +1387,10 @@ 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;
>
>
David Miller Aug. 30, 2017, 10:55 p.m. | #2
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Wed, 30 Aug 2017 09:29:31 -0700

> From: Eric Dumazet <edumazet@google.com>
> 
> 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@google.com>
> Reported-by: Dmitry Vyukov <dvyukov@google.com>

Applied and queued up for -stable, thanks.

Patch

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index 48e993b2dbcf1afae04968ed840e2e98c2cf6772..af4e76ac88ff0817398d1d7460a41f0cd5fe6f30 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -1387,6 +1387,10 @@  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;