[3.8.y.z extended stable] Patch "selinux: handle TCP SYN-ACK packets correctly in" has been added to staging queue

Kamal Mostafa kamal at canonical.com
Fri Jan 3 23:15:02 UTC 2014


This is a note to let you know that I have just added a patch titled

    selinux: handle TCP SYN-ACK packets correctly in

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.16.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 18f6451c115262a47a514198298bdf60f3eb199d Mon Sep 17 00:00:00 2001
From: Paul Moore <pmoore at redhat.com>
Date: Wed, 4 Dec 2013 16:10:51 -0500
Subject: selinux: handle TCP SYN-ACK packets correctly in
 selinux_ip_postroute()

commit 446b802437f285de68ffb8d6fac3c44c3cab5b04 upstream.

In selinux_ip_postroute() we perform access checks based on the
packet's security label.  For locally generated traffic we get the
packet's security label from the associated socket; this works in all
cases except for TCP SYN-ACK packets.  In the case of SYN-ACK packet's
the correct security label is stored in the connection's request_sock,
not the server's socket.  Unfortunately, at the point in time when
selinux_ip_postroute() is called we can't query the request_sock
directly, we need to recreate the label using the same logic that
originally labeled the associated request_sock.

See the inline comments for more explanation.

Reported-by: Janak Desai <Janak.Desai at gtri.gatech.edu>
Tested-by: Janak Desai <Janak.Desai at gtri.gatech.edu>
Signed-off-by: Paul Moore <pmoore at redhat.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 security/selinux/hooks.c | 68 +++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 53 insertions(+), 15 deletions(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index ef26e96..a3d77ec 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3713,6 +3713,30 @@ static int selinux_skb_peerlbl_sid(struct sk_buff *skb, u16 family, u32 *sid)
 	return 0;
 }

+/**
+ * selinux_conn_sid - Determine the child socket label for a connection
+ * @sk_sid: the parent socket's SID
+ * @skb_sid: the packet's SID
+ * @conn_sid: the resulting connection SID
+ *
+ * If @skb_sid is valid then the user:role:type information from @sk_sid is
+ * combined with the MLS information from @skb_sid in order to create
+ * @conn_sid.  If @skb_sid is not valid then then @conn_sid is simply a copy
+ * of @sk_sid.  Returns zero on success, negative values on failure.
+ *
+ */
+static int selinux_conn_sid(u32 sk_sid, u32 skb_sid, u32 *conn_sid)
+{
+	int err = 0;
+
+	if (skb_sid != SECSID_NULL)
+		err = security_sid_mls_copy(sk_sid, skb_sid, conn_sid);
+	else
+		*conn_sid = sk_sid;
+
+	return err;
+}
+
 /* socket security operations */

 static int socket_sockcreate_sid(const struct task_security_struct *tsec,
@@ -4319,7 +4343,7 @@ static int selinux_inet_conn_request(struct sock *sk, struct sk_buff *skb,
 	struct sk_security_struct *sksec = sk->sk_security;
 	int err;
 	u16 family = sk->sk_family;
-	u32 newsid;
+	u32 connsid;
 	u32 peersid;

 	/* handle mapped IPv4 packets arriving via IPv6 sockets */
@@ -4329,16 +4353,11 @@ static int selinux_inet_conn_request(struct sock *sk, struct sk_buff *skb,
 	err = selinux_skb_peerlbl_sid(skb, family, &peersid);
 	if (err)
 		return err;
-	if (peersid == SECSID_NULL) {
-		req->secid = sksec->sid;
-		req->peer_secid = SECSID_NULL;
-	} else {
-		err = security_sid_mls_copy(sksec->sid, peersid, &newsid);
-		if (err)
-			return err;
-		req->secid = newsid;
-		req->peer_secid = peersid;
-	}
+	err = selinux_conn_sid(sksec->sid, peersid, &connsid);
+	if (err)
+		return err;
+	req->secid = connsid;
+	req->peer_secid = peersid;

 	return selinux_netlbl_inet_conn_request(req, family);
 }
@@ -4687,12 +4706,12 @@ static unsigned int selinux_ip_postroute(struct sk_buff *skb, int ifindex,
 	if (!secmark_active && !peerlbl_active)
 		return NF_ACCEPT;

-	/* if the packet is being forwarded then get the peer label from the
-	 * packet itself; otherwise check to see if it is from a local
-	 * application or the kernel, if from an application get the peer label
-	 * from the sending socket, otherwise use the kernel's sid */
 	sk = skb->sk;
 	if (sk == NULL) {
+		/* Without an associated socket the packet is either coming
+		 * from the kernel or it is being forwarded; check the packet
+		 * to determine which and if the packet is being forwarded
+		 * query the packet directly to determine the security label. */
 		if (skb->skb_iif) {
 			secmark_perm = PACKET__FORWARD_OUT;
 			if (selinux_skb_peerlbl_sid(skb, family, &peer_sid))
@@ -4701,7 +4720,26 @@ static unsigned int selinux_ip_postroute(struct sk_buff *skb, int ifindex,
 			secmark_perm = PACKET__SEND;
 			peer_sid = SECINITSID_KERNEL;
 		}
+	} else if (sk->sk_state == TCP_LISTEN) {
+		/* Locally generated packet but the associated socket is in the
+		 * listening state which means this is a SYN-ACK packet.  In
+		 * this particular case the correct security label is assigned
+		 * to the connection/request_sock but unfortunately we can't
+		 * query the request_sock as it isn't queued on the parent
+		 * socket until after the SYN-ACK packet is sent; the only
+		 * viable choice is to regenerate the label like we do in
+		 * selinux_inet_conn_request().  See also selinux_ip_output()
+		 * for similar problems. */
+		u32 skb_sid;
+		struct sk_security_struct *sksec = sk->sk_security;
+		if (selinux_skb_peerlbl_sid(skb, family, &skb_sid))
+			return NF_DROP;
+		if (selinux_conn_sid(sksec->sid, skb_sid, &peer_sid))
+			return NF_DROP;
+		secmark_perm = PACKET__SEND;
 	} else {
+		/* Locally generated packet, fetch the security label from the
+		 * associated socket. */
 		struct sk_security_struct *sksec = sk->sk_security;
 		peer_sid = sksec->sid;
 		secmark_perm = PACKET__SEND;
--
1.8.3.2





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