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

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Message-Id: <20170209120301.28152-1-colin.king@canonical.com>
Date:   Thu,  9 Feb 2017 12:03:01 +0000
From:   Colin King <colin.king@...onical.com>
To:     Casey Schaufler <casey@...aufler-ca.com>,
        James Morris <james.l.morris@...cle.com>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        linux-security-module@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] 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.

Detected with CoverityScan, CID#1324196 ("Dereference before null check")

Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 security/smack/smack_lsm.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index fc8fb31..bb17387 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -2899,7 +2899,7 @@ static int smack_socket_connect(struct socket *sock, struct sockaddr *sap,
 #endif
 #ifdef SMACK_IPV6_SECMARK_LABELING
 	struct smack_known *rsp;
-	struct socket_smack *ssp = sock->sk->sk_security;
+	struct socket_smack *ssp;
 #endif
 
 	if (sock->sk == NULL)
@@ -2916,9 +2916,11 @@ static int smack_socket_connect(struct socket *sock, struct sockaddr *sap,
 			return -EINVAL;
 #ifdef SMACK_IPV6_SECMARK_LABELING
 		rsp = smack_ipv6host_label(sip);
-		if (rsp != NULL)
+		if (rsp != NULL) {
+			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