From 04d450668aa58e6202916ad870cdfc73621dee26 Mon Sep 17 00:00:00 2001 From: David Howells Date: Thu, 31 Mar 2011 11:58:52 -0700 Subject: [PATCH] Patch cab9e9848b9a8283b0504a2d7c435a9f5ba026de to the 2.6.35.y stable tree stored a ref to the current cred struct in struct scm_cookie. This was fine with AF_UNIX as that calls scm_destroy() from its packet sending functions, but AF_NETLINK, which also uses scm_send(), does not call scm_destroy() - meaning that the copied credentials leak each time SCM data is sent over a netlink socket. This can be triggered quite simply on a Fedora 13 or 14 userspace with the 2.6.35.11 kernel (or something based off of that) by calling: #!/bin/bash for ((i=0; i<100; i++)) do su - -c /bin/true cut -d: -f1 /proc/slabinfo | grep 'cred\|key\|task_struct' cat /proc/keys | wc -l done This leaks the session key that pam_keyinit creates for 'su -', which appears in /proc/keys as being revoked (has the R flag set against it) afterward su is called. Furthermore, if CONFIG_SLAB=y, then the cred and key slab object usage counts can be viewed and seen to increase. The key slab increases by one object per loop, and this can be seen after the system has had a couple of minutes to stand after the script above has been run on it. If the system is working correctly, the key and cred counts should return to roughly what they were before. This patch from upstream (b47030c71dfd6c8cd5cb6e551b6f7f7cfc96f6a6) is needed to fix the problem: =============================================================================== From: Eric W. Biederman af_netlink: Add needed scm_destroy after scm_send. scm_send occasionally allocates state in the scm_cookie, so I have modified netlink_sendmsg to guarantee that when scm_send succeeds scm_destory will be called to free that state. Signed-off-by: Eric W. Biederman Signed-off-by: Andi Kleen Reviewed-by: Daniel Lezcano Acked-by: Pavel Emelyanov Signed-off-by: David S. Miller --- net/netlink/af_netlink.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c index 56ed59eea69c..eb1647873261 100644 --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -1323,8 +1323,11 @@ static int netlink_sendmsg(struct kiocb *kiocb, struct socket *sock, if (msg->msg_flags&MSG_OOB) return -EOPNOTSUPP; - if (NULL == siocb->scm) + if (NULL == siocb->scm) { siocb->scm = &scm; + memset(&scm, 0, sizeof(scm)); + } + err = scm_send(sock, msg, siocb->scm); if (err < 0) return err; -- 2.39.5