netdev - Re: linux-next: build warning after merge of the bpf-next tree

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Date:   Sun, 24 Mar 2019 18:39:26 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Stephen Rothwell <sfr@...b.auug.org.au>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Networking <netdev@...r.kernel.org>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        David Miller <davem@...emloft.net>
Subject: Re: linux-next: build warning after merge of the bpf-next tree

On Sun, Mar 24, 2019 at 6:30 PM Stephen Rothwell <sfr@...b.auug.org.au> wrote:
>
> Hi all,
>
> After merging the bpf-next tree, today's linux-next build (x86_64
> allmodconfig) produced this warning:
>
> net/core/filter.c: In function 'bpf_skb_adjust_room':
> net/core/filter.c:3022:31: warning: 'inner_trans' may be used uninitialized in this function [-Wmaybe-uninitialized]
>    skb->inner_transport_header = inner_trans;
>    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~
> net/core/filter.c:2979:26: note: 'inner_trans' was declared here
>   u16 mac_len, inner_net, inner_trans;
>                           ^~~~~~~~~~~
> net/core/filter.c:3021:29: warning: 'inner_net' may be used uninitialized in this function [-Wmaybe-uninitialized]
>    skb->inner_network_header = inner_net;
>    ~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~
> net/core/filter.c:2979:15: note: 'inner_net' was declared here
>   u16 mac_len, inner_net, inner_trans;
>                ^~~~~~~~~
> net/core/filter.c:3026:3: warning: 'mac_len' may be used uninitialized in this function [-Wmaybe-uninitialized]
>    skb_set_network_header(skb, mac_len);
>    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> net/core/filter.c:2979:6: note: 'mac_len' was declared here
>   u16 mac_len, inner_net, inner_trans;
>       ^~~~~~~
>
> Introduced by commit
>
>   868d523535c2 ("bpf: add bpf_skb_adjust_room encap flags")
>
>
> This looks like a false positive, it seems that they are only set and
> used when encap is true.

Indeed. Sorry about that.

The fix for this is now in bpf-next, commit 62b31b42cff9 ("bpf:
silence uninitialized var warning in bpf_skb_net_grow").