linux-kernel - re: netfilter: nft_ct: add ct expectations support

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Message-ID: <dadf225f-3003-72ba-d7b5-e0467bb77ffc@canonical.com>
Date:   Tue, 18 Jun 2019 14:57:29 +0100
From:   Colin Ian King <colin.king@...onical.com>
To:     Stéphane Veyret <sveyret@...il.com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        "David S. Miller" <davem@...emloft.net>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: re: netfilter: nft_ct: add ct expectations support

Hi,

Static analysis with Coverity on linux-next has found a potential issue
with the following commit:

commit 857b46027d6f91150797295752581b7155b9d0e1
Author: Stéphane Veyret <sveyret@...il.com>
Date:   Sat May 25 15:30:58 2019 +0200

    netfilter: nft_ct: add ct expectations support


Specifically in function nft_ct_expect_obj_eval)() in the following code:

+       help = nfct_help(ct);
+       if (!help)
+               help = nf_ct_helper_ext_add(ct, GFP_ATOMIC);
+
+       if (help->expecting[NF_CT_EXPECT_CLASS_DEFAULT] >= priv->size) {
+               regs->verdict.code = NFT_BREAK;
+               return;
+       }


The call to nf_ct_helper_ext_add can potentially return NULL, however,
this is not being checked and pointer 'help' is being dereferenced even
though it potentially can be null.

Colin