netdev - [PATCH net] selinux: fix random read in selinux_ip_postroute

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Date:	Thu, 05 Nov 2015 13:39:24 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Dmitry Vyukov <dvyukov@...gle.com>,
	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>, Paul Moore <paul@...l-moore.com>
Subject: [PATCH net] selinux: fix random read in
 selinux_ip_postroute_compat()

From: Eric Dumazet <edumazet@...gle.com>

In commit e446f9dfe17b ("net: synack packets can be attached to request
sockets"), I missed one remaining case of invalid skb->sk->sk_security
access.

Dmitry Vyukov got a KASan report pointing to it.

Add selinux_skb_sk() helper that is responsible to get back to the
listener if skb is attached to a request socket, instead of
duplicating the logic.

Fixes: ca6fb0651883 ("tcp: attach SYNACK messages to request sockets instead of listener")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Paul Moore <paul@...l-moore.com>
---
 security/selinux/hooks.c |   18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 26f4039d54b8..c9b2d5467477 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -4931,11 +4931,23 @@ static unsigned int selinux_ipv4_output(void *priv,
 	return selinux_ip_output(skb, PF_INET);
 }
 
+/* SYNACK messages might be attached to request sockets.
+ * To get back to sk_security, we need to look at the listener.
+ */
+static struct sock *selinux_skb_sk(const struct sk_buff *skb)
+{
+	struct sock *sk = skb->sk;
+
+	if (sk && sk->sk_state == TCP_NEW_SYN_RECV)
+		sk = inet_reqsk(sk)->rsk_listener;
+	return sk;
+}
+
 static unsigned int selinux_ip_postroute_compat(struct sk_buff *skb,
 						int ifindex,
 						u16 family)
 {
-	struct sock *sk = skb->sk;
+	struct sock *sk = selinux_skb_sk(skb);
 	struct sk_security_struct *sksec;
 	struct common_audit_data ad;
 	struct lsm_network_audit net = {0,};
@@ -4990,7 +5002,7 @@ static unsigned int selinux_ip_postroute(struct sk_buff *skb,
 	if (!secmark_active && !peerlbl_active)
 		return NF_ACCEPT;
 
-	sk = skb->sk;
+	sk = selinux_skb_sk(skb);
 
 #ifdef CONFIG_XFRM
 	/* If skb->dst->xfrm is non-NULL then the packet is undergoing an IPsec
@@ -5035,8 +5047,6 @@ static unsigned int selinux_ip_postroute(struct sk_buff *skb,
 		u32 skb_sid;
 		struct sk_security_struct *sksec;
 
-		if (sk->sk_state == TCP_NEW_SYN_RECV)
-			sk = inet_reqsk(sk)->rsk_listener;
 		sksec = sk->sk_security;
 		if (selinux_skb_peerlbl_sid(skb, family, &skb_sid))
 			return NF_DROP;


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