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")
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
