linux-kernel - [PATCH] netfilter: nf_flow_table: big endian fix for TCP flags

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Date:   Thu, 19 Dec 2019 15:40:47 -0800
From:   Olof Johansson <olof@...om.net>
To:     Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>
Cc:     coreteam@...filter.org, netfilter-devel@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Olof Johansson <olof@...om.net>
Subject: [PATCH] netfilter: nf_flow_table: big endian fix for TCP flags

TCP_FLAG_* are 32-bit big endian constants, not 16-bit. So on big endian
machines, you need to shift them down to fit the 16-bit tcp.mask here.

This surfaced through ARM allmodconfig, which is big endian:

net/netfilter/nf_flow_table_offload.c: In function 'nf_flow_rule_match':
net/netfilter/nf_flow_table_offload.c:91:21: warning: unsigned conversion from 'int' to '__be16' {aka 'short unsigned int'} changes value from '327680' to '0' [-Woverflow]

Need to convert to/from host word order to keep LE/BE behaving the same.

Fixes: c29f74e0df7a ("netfilter: nf_flow_table: hardware offload support")
Signed-off-by: Olof Johansson <olof@...om.net>
---
 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 de7a0d1e15c88..e32ff796378c6 100644
--- a/net/netfilter/nf_flow_table_offload.c
+++ b/net/netfilter/nf_flow_table_offload.c
@@ -88,7 +88,7 @@ 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 = htons(ntohl(TCP_FLAG_RST | TCP_FLAG_FIN) >> 16);
 		match->dissector.used_keys |= BIT(FLOW_DISSECTOR_KEY_TCP);
 		break;
 	case IPPROTO_UDP:
-- 
2.11.0