[PATCH Precise CVE-2012-3520] af_netlink: force credentials passing [CVE-2012-3520]

[Tim Gardner]

From: Eric Dumazet <edumazet at google.com>

CVE-2012-3520

BugLink: http://bugs.launchpad.net/bugs/1052097

Pablo Neira Ayuso discovered that avahi and
potentially NetworkManager accept spoofed Netlink messages because of a
kernel bug.  The kernel passes all-zero SCM_CREDENTIALS ancillary data
to the receiver if the sender did not provide such data, instead of not
including any such data at all or including the correct data from the
peer (as it is the case with AF_UNIX).

This bug was introduced in commit 16e572626961
(af_unix: dont send SCM_CREDENTIALS by default)

This patch forces passing credentials for netlink, as
before the regression.

Another fix would be to not add SCM_CREDENTIALS in
netlink messages if not provided by the sender, but it
might break some programs.

With help from Florian Weimer & Petr Matousek

This issue is designated as CVE-2012-3520

Signed-off-by: Eric Dumazet <edumazet at google.com>
Cc: Petr Matousek <pmatouse at redhat.com>
Cc: Florian Weimer <fweimer at redhat.com>
Cc: Pablo Neira Ayuso <pablo at netfilter.org>
Signed-off-by: David S. Miller <davem at davemloft.net>
(cherry picked from commit e0e3cea46d31d23dc40df0a49a7a2c04fe8edfea)

Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
---
 include/net/scm.h        |    4 +++-
 net/netlink/af_netlink.c |    2 +-
 net/unix/af_unix.c       |    4 ++--
 3 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/include/net/scm.h b/include/net/scm.h
index d456f4c..0c0017c 100644
--- a/include/net/scm.h
+++ b/include/net/scm.h
@@ -71,9 +71,11 @@ static __inline__ void scm_destroy(struct scm_cookie *scm)
 }
 
 static __inline__ int scm_send(struct socket *sock, struct msghdr *msg,
-			       struct scm_cookie *scm)
+			       struct scm_cookie *scm, bool forcecreds)
 {
 	memset(scm, 0, sizeof(*scm));
+	if (forcecreds)
+		scm_set_cred(scm, task_tgid(current), current_cred());
 	unix_get_peersec_dgram(sock, scm);
 	if (msg->msg_controllen <= 0)
 		return 0;
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index b3025a6..0e67760 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1344,7 +1344,7 @@ static int netlink_sendmsg(struct kiocb *kiocb, struct socket *sock,
 	if (NULL == siocb->scm)
 		siocb->scm = &scm;
 
-	err = scm_send(sock, msg, siocb->scm);
+	err = scm_send(sock, msg, siocb->scm, true);
 	if (err < 0)
 		return err;
 
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 641f2e4..9aa708c 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1448,7 +1448,7 @@ static int unix_dgram_sendmsg(struct kiocb *kiocb, struct socket *sock,
 	if (NULL == siocb->scm)
 		siocb->scm = &tmp_scm;
 	wait_for_unix_gc();
-	err = scm_send(sock, msg, siocb->scm);
+	err = scm_send(sock, msg, siocb->scm, false);
 	if (err < 0)
 		return err;
 
@@ -1617,7 +1617,7 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock,
 	if (NULL == siocb->scm)
 		siocb->scm = &tmp_scm;
 	wait_for_unix_gc();
-	err = scm_send(sock, msg, siocb->scm);
+	err = scm_send(sock, msg, siocb->scm, false);
 	if (err < 0)
 		return err;
 
-- 
1.7.9.5