linux-kernel - Re: [ 105/124] af_unix: dont send SCM_CREDENTIAL when dest socket is NULL

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Message-ID: <1365014637.13853.36.camel@edumazet-glaptop>
Date:	Wed, 03 Apr 2013 11:43:57 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Andy Lutomirski <luto@...capital.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Sven Joachim <svenjoac@....de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Ding Tianhong <dingtianhong@...wei.com>,
	Eric Dumazet <edumazet@...gle.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [ 105/124] af_unix: dont send SCM_CREDENTIAL when dest socket
 is NULL

On Wed, 2013-04-03 at 10:58 -0700, Andy Lutomirski wrote:

> 
> This sounds suspiciously like an SCM_CREDENTIALS bug triggered by a
> race.  There's a fix (that needs both a new version from me and a review
> by someone) here:
> 
> http://www.spinics.net/lists/netdev/msg229948.html

Hmm... this is not a stable candidate, IMHO.

This has to be fixed (if needed) in a more easy way. 

What about this one liner ?

CC Eric W. Biederman  as he wrote commit
dbe9a4173ea53b72b2c3
(scm: Don't use struct ucred in NETLINK_CB and struct scm_cookie.)

diff --git a/include/net/scm.h b/include/net/scm.h
index 975cca0..42359d8 100644
--- a/include/net/scm.h
+++ b/include/net/scm.h
@@ -120,7 +120,7 @@ static __inline__ void scm_recv(struct socket *sock, struct msghdr *msg,
 		return;
 	}
 
-	if (test_bit(SOCK_PASSCRED, &sock->flags)) {
+	if (test_bit(SOCK_PASSCRED, &sock->flags) && scm->creds.pid) {
 		struct user_namespace *current_ns = current_user_ns();
 		struct ucred ucreds = {
 			.pid = scm->creds.pid,


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