security: smack: Fix possible null-pointer dereferences in smack_socket_sock_rcv_skb()

BugLink: https://bugs.launchpad.net/bugs/1848274
[ 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@gmail.com>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 0d45c7884f50627f3849041ab65b28150cac40ea..e593d449672bc29992c0b1ea75d080846a16b6f9 100644 (file)
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -3839,6 +3839,8 @@ access_check:
                        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;