linux-kernel - [PATCH] netfilter: nf_flow_table: fix big-endian integer overflow

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Message-Id: <20191210202443.2226043-1-arnd@arndb.de>
Date:   Tue, 10 Dec 2019 21:24:28 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        "David S. Miller" <davem@...emloft.net>
Cc:     Arnd Bergmann <arnd@...db.de>, wenxu <wenxu@...oud.cn>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] netfilter: nf_flow_table: fix big-endian integer overflow

In some configurations, gcc reports an integer overflow:

net/netfilter/nf_flow_table_offload.c: In function 'nf_flow_rule_match':
net/netfilter/nf_flow_table_offload.c:80:21: error: unsigned conversion from 'int' to '__be16' {aka 'short unsigned int'} changes value from '327680' to '0' [-Werror=overflow]
   mask->tcp.flags = TCP_FLAG_RST | TCP_FLAG_FIN;
                     ^~~~~~~~~~~~

>From what I can tell, we want the upper 16 bits of these constants,
so they need to be shifted in cpu-endian mode.

Fixes: c29f74e0df7a ("netfilter: nf_flow_table: hardware offload support")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
I'm not sure if this is the correct fix, please check carefully
---
 net/netfilter/nf_flow_table_offload.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netfilter/nf_flow_table_offload.c b/net/netfilter/nf_flow_table_offload.c
index c54c9a6cc981..24543c45d501 100644
--- a/net/netfilter/nf_flow_table_offload.c
+++ b/net/netfilter/nf_flow_table_offload.c
@@ -77,7 +77,7 @@ static int nf_flow_rule_match(struct nf_flow_match *match,
 	switch (tuple->l4proto) {
 	case IPPROTO_TCP:
 		key->tcp.flags = 0;
-		mask->tcp.flags = TCP_FLAG_RST | TCP_FLAG_FIN;
+		mask->tcp.flags = cpu_to_be16(be32_to_cpu(TCP_FLAG_RST | TCP_FLAG_FIN) >> 16);
 		match->dissector.used_keys |= BIT(FLOW_DISSECTOR_KEY_TCP);
 		break;
 	case IPPROTO_UDP:
-- 
2.20.0