Hi Geert, On Tue, Nov 26, 2019 at 12:06:03PM +0100, Geert Uytterhoeven wrote: > On Thu, Nov 21, 2019 at 8:36 AM Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> wrote: > > After merging the net-next tree, today's linux-next build (powerpc > > allyesconfig) produced this warning: > > > > net/netfilter/nf_flow_table_offload.c: In function 'nf_flow_rule_match': > > net/netfilter/nf_flow_table_offload.c:80:21: warning: unsigned conversion from 'int' to '__be16' {aka 'short unsigned int'} changes value from '327680' to '0' [-Woverflow] > > 80 | mask->tcp.flags = TCP_FLAG_RST | TCP_FLAG_FIN; > > | ^~~~~~~~~~~~ > > > > Introduced by commit > > > > c29f74e0df7a ("netfilter: nf_flow_table: hardware offload support") > > This is now upstream, and must be completely broken on big-endian > platforms. > > The other user of the flags field looks buggy, too > (net/core/flow_dissector.c:__skb_flow_dissect_tcp()[*]): > > key_tcp->flags = (*(__be16 *) &tcp_flag_word(th) & htons(0x0FFF)); > > Disclaimer: I'm not familiar with the code or protocol, so below are just > my gut feelings. > > struct flow_dissector_key_tcp { > __be16 flags; > }; > > Does this have to be __be16, i.e. does it go over the wire? > If not, this should probably be __u16, and set using > "be32_to_cpu(flags) >> 16"? > If yes, "cpu_to_be16(be32_to_cpu(flags) >> 16)"? > (Ugh, needs convenience macros) > > [*] ac4bb5de27010e41 ("net: flow_dissector: add support for dissection > of tcp flags") I'm attaching a tentative patch, please let me know this is fixing up this issue there. Thanks.
diff --git a/include/net/flow_dissector.h b/include/net/flow_dissector.h index b8c20e9f343e..30ad4e07ff52 100644 --- a/include/net/flow_dissector.h +++ b/include/net/flow_dissector.h @@ -189,10 +189,17 @@ struct flow_dissector_key_eth_addrs { /** * struct flow_dissector_key_tcp: - * @flags: flags + * @flags: TCP flags (16-bit, including the initial Data offset field bits) + * @word: Data offset + reserved bits + TCP flags + window */ struct flow_dissector_key_tcp { - __be16 flags; + union { + struct { + __be16 flags; + __be16 __pad; + }; + __be32 flag_word; + }; }; /** diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c index ca871657a4c4..83af4633f306 100644 --- a/net/core/flow_dissector.c +++ b/net/core/flow_dissector.c @@ -756,7 +756,7 @@ __skb_flow_dissect_tcp(const struct sk_buff *skb, key_tcp = skb_flow_dissector_target(flow_dissector, FLOW_DISSECTOR_KEY_TCP, target_container); - key_tcp->flags = (*(__be16 *) &tcp_flag_word(th) & htons(0x0FFF)); + key_tcp->flag_word = tcp_flag_word(th); } static void diff --git a/net/netfilter/nf_flow_table_offload.c b/net/netfilter/nf_flow_table_offload.c index c94ebad78c5c..30205d57226d 100644 --- a/net/netfilter/nf_flow_table_offload.c +++ b/net/netfilter/nf_flow_table_offload.c @@ -87,8 +87,8 @@ 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; + key->tcp.flag_word = 0; + mask->tcp.flag_word = TCP_FLAG_RST | TCP_FLAG_FIN; match->dissector.used_keys |= BIT(FLOW_DISSECTOR_KEY_TCP); break; case IPPROTO_UDP: