linux-kernel - [PATCH AUTOSEL 4.9 08/13] security: smack: Fix possible null-pointer dereferences in smack_socket_sock_rcv

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Message-Id: <20190929173625.10003-8-sashal@kernel.org>
Date:   Sun, 29 Sep 2019 13:36:18 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Jia-Ju Bai <baijiaju1990@...il.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Sasha Levin <sashal@...nel.org>,
        linux-security-module@...r.kernel.org
Subject: [PATCH AUTOSEL 4.9 08/13] security: smack: Fix possible null-pointer dereferences in smack_socket_sock_rcv_skb()

From: Jia-Ju Bai <baijiaju1990@...il.com>

[ Upstream commit 3f4287e7d98a2954f20bf96c567fdffcd2b63eb9 ]

In smack_socket_sock_rcv_skb(), there is an if statement
on line 3920 to check whether skb is NULL:
    if (skb && skb->secmark != 0)

This check indicates skb can be NULL in some cases.

But on lines 3931 and 3932, skb is used:
    ad.a.u.net->netif = skb->skb_iif;
    ipv6_skb_to_auditdata(skb, &ad.a, NULL);

Thus, possible null-pointer dereferences may occur when skb is NULL.

To fix these possible bugs, an if statement is added to check skb.

These bugs are found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 security/smack/smack_lsm.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index aeb3ba70f9077..19d1702aa9856 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -4037,6 +4037,8 @@ static int smack_socket_sock_rcv_skb(struct sock *sk, struct sk_buff *skb)
 			skp = smack_ipv6host_label(&sadd);
 		if (skp == NULL)
 			skp = smack_net_ambient;
+		if (skb == NULL)
+			break;
 #ifdef CONFIG_AUDIT
 		smk_ad_init_net(&ad, __func__, LSM_AUDIT_DATA_NET, &net);
 		ad.a.u.net->family = family;
-- 
2.20.1