linux-kernel - [PATCH][next] netfilter: nf_tables: Fix dereference of null pointer flow

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Message-Id: <20210624195718.170796-1-colin.king@canonical.com>
Date:   Thu, 24 Jun 2021 20:57:18 +0100
From:   Colin King <colin.king@...onical.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH][next] netfilter: nf_tables: Fix dereference of null pointer flow

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

In the case where chain->flags & NFT_CHAIN_HW_OFFLOAD is false then
nft_flow_rule_create is not called and flow is NULL. The subsequent
error handling execution via label err_destroy_flow_rule will lead
to a null pointer dereference on flow when calling nft_flow_rule_destroy.
Since the error path to err_destroy_flow_rule has to cater for null
and non-null flows, only call nft_flow_rule_destroy if flow is non-null
to fix this issue.

Addresses-Coverity: ("Explicity null dereference")
Fixes: 3c5e44622011 ("netfilter: nf_tables: memleak in hw offload abort path")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 net/netfilter/nf_tables_api.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index 390d4466567f..de182d1f7c4e 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -3446,7 +3446,8 @@ static int nf_tables_newrule(struct sk_buff *skb, const struct nfnl_info *info,
 	return 0;
 
 err_destroy_flow_rule:
-	nft_flow_rule_destroy(flow);
+	if (flow)
+		nft_flow_rule_destroy(flow);
 err_release_rule:
 	nf_tables_rule_release(&ctx, rule);
 err_release_expr:
-- 
2.31.1