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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Tue, 26 Nov 2019 13:22:47 -0800
Message-ID: <CAKwvOdk5wZF6BHR0_xSL=H=tmSFT42qmn23etO3uV6w-PPgaqA@mail.gmail.com>
Subject: Re: [PATCH] netfilter: nf_flow_table_offload: Don't use offset
 uninitialized in flow_offload_port_{d,s}nat
To:     Nathan Chancellor <natechancellor@gmail.com>
Cc:     Pablo Neira Ayuso <pablo@netfilter.org>,
        Jozsef Kadlecsik <kadlec@netfilter.org>,
        Florian Westphal <fw@strlen.de>,
        netfilter-devel@vger.kernel.org, coreteam@netfilter.org,
        Network Development <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>
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On Tue, Nov 26, 2019 at 12:13 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> Clang warns (trimmed the second warning for brevity):
>
> ../net/netfilter/nf_flow_table_offload.c:342:2: warning: variable
> 'offset' is used uninitialized whenever switch default is taken
> [-Wsometimes-uninitialized]
>         default:
>         ^~~~~~~
> ../net/netfilter/nf_flow_table_offload.c:346:57: note: uninitialized use
> occurs here
>         flow_offload_mangle(entry, flow_offload_l4proto(flow), offset,
>                                                                ^~~~~~
> ../net/netfilter/nf_flow_table_offload.c:331:12: note: initialize the
> variable 'offset' to silence this warning
>         u32 offset;
>                   ^
>                    = 0
>
> Match what was done in the flow_offload_ipv{4,6}_{d,s}nat functions and
> just return in the default case, since port would also be uninitialized.

Thanks for the patch. I have a report of this from kernelci bot, would
you mind crediting it:
Reported-by: kernelci.org bot <bot@kernelci.org>
Looks like `port` is uninitialized (prior to your patch), too.
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
These two functions look identical except for the mask. The
maintainers should consider reusing more code between them and passing
in the mask.

>
> Fixes: c29f74e0df7a ("netfilter: nf_flow_table: hardware offload support")
> Link: https://github.com/ClangBuiltLinux/linux/issues/780
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> ---
>  net/netfilter/nf_flow_table_offload.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/netfilter/nf_flow_table_offload.c b/net/netfilter/nf_flow_table_offload.c
> index c54c9a6cc981..a77a6e1cfd64 100644
> --- a/net/netfilter/nf_flow_table_offload.c
> +++ b/net/netfilter/nf_flow_table_offload.c
> @@ -340,7 +340,7 @@ static void flow_offload_port_snat(struct net *net,
>                 offset = 0; /* offsetof(struct tcphdr, dest); */
>                 break;
>         default:
> -               break;
> +               return;
>         }
>
>         flow_offload_mangle(entry, flow_offload_l4proto(flow), offset,
> @@ -367,7 +367,7 @@ static void flow_offload_port_dnat(struct net *net,
>                 offset = 0; /* offsetof(struct tcphdr, dest); */
>                 break;
>         default:
> -               break;
> +               return;
>         }
>
>         flow_offload_mangle(entry, flow_offload_l4proto(flow), offset,
> --
> 2.24.0
>
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-- 
Thanks,
~Nick Desaulniers