selinux: fix random read in selinux_ip_postroute_compat()

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@google.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Paul Moore <paul@paul-moore.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files 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;