linux-kernel - [PATCH][V2] Smack: fix a dereference before null check on sock->sk

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Message-Id: <20170209171127.5029-1-colin.king@canonical.com>
Date:   Thu,  9 Feb 2017 17:11:27 +0000
From:   Colin King <colin.king@...onical.com>
To:     Casey Schaufler <casey@...aufler-ca.com>,
        James Morris <james.l.morris@...cle.com>,
        "Serge E . Hally" <serge@...lyn.com>,
        linux-security-module@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH][V2] Smack: fix a dereference before null check on sock->sk

From: Colin Ian King <colin.king@...onical.com>

The initialisation of pointer ssp is from a dereference on sock->sk
before sock-sk is null checked, hence there is a potential for a
null pointer deference.  Fix this by moving the assignment of ssp
to just before it is used in the call to smk_ipv6_check.

Also minor clean up of code to reduce #ifdef noise.
Detected with CoverityScan, CID#1324196 ("Dereference before null check")

Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 security/smack/smack_lsm.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index fc8fb31..0c5656d 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -2897,10 +2897,6 @@ static int smack_socket_connect(struct socket *sock, struct sockaddr *sap,
 #if IS_ENABLED(CONFIG_IPV6)
 	struct sockaddr_in6 *sip = (struct sockaddr_in6 *)sap;
 #endif
-#ifdef SMACK_IPV6_SECMARK_LABELING
-	struct smack_known *rsp;
-	struct socket_smack *ssp = sock->sk->sk_security;
-#endif
 
 	if (sock->sk == NULL)
 		return 0;
@@ -2915,10 +2911,17 @@ static int smack_socket_connect(struct socket *sock, struct sockaddr *sap,
 		if (addrlen < sizeof(struct sockaddr_in6))
 			return -EINVAL;
 #ifdef SMACK_IPV6_SECMARK_LABELING
-		rsp = smack_ipv6host_label(sip);
-		if (rsp != NULL)
-			rc = smk_ipv6_check(ssp->smk_out, rsp, sip,
-						SMK_CONNECTING);
+		{
+			struct smack_known *rsp = smack_ipv6host_label(sip);
+
+			if (rsp != NULL) {
+				struct socket_smack *ssp =
+					sock->sk->sk_security;
+
+				rc = smk_ipv6_check(ssp->smk_out, rsp, sip,
+						    SMK_CONNECTING);
+			}
+		}
 #endif
 #ifdef SMACK_IPV6_PORT_LABELING
 		rc = smk_ipv6_port_check(sock->sk, sip, SMK_CONNECTING);
-- 
2.10.2