netdev - Re: [PATCH] net: avoid uninitialized variable

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Date:   Thu, 27 Oct 2016 12:02:57 +0800
From:   Gao Feng <fgao@...ai8.com>
To:     zhongjiang <zhongjiang@...wei.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Alex Duyck <aduyck@...antis.com>,
        Tom Herbert <tom@...bertland.com>, jiri@...lanox.com,
        hadarh@...lanox.com, amir@...ai.me,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: avoid uninitialized variable

On Thu, Oct 27, 2016 at 11:56 AM, zhongjiang <zhongjiang@...wei.com> wrote:
> From: zhong jiang <zhongjiang@...wei.com>
>
> when I compiler the newest kernel, I hit the following error with
> Werror=may-uninitalized.
>
> net/core/flow_dissector.c: In function ?._skb_flow_dissect?
> include/uapi/linux/swab.h:100:46: error: ?.lan?.may be used uninitialized in this function [-Werror=maybe-uninitialized]
> net/core/flow_dissector.c:248:26: note: ?.lan?.was declared here
>
> This adds an additional check for proto to explicitly tell the compiler
> that vlan pointer have the correct value before it is used.
>
> Signed-off-by: zhong jiang <zhongjiang@...wei.com>
> ---
>  net/core/flow_dissector.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
> index 1a7b80f..a04d9cf 100644
> --- a/net/core/flow_dissector.c
> +++ b/net/core/flow_dissector.c
> @@ -245,7 +245,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
>         }
>         case htons(ETH_P_8021AD):
>         case htons(ETH_P_8021Q): {
> -               const struct vlan_hdr *vlan;
> +               const struct vlan_hdr *vlan = NULL;
>
>                 if (skb_vlan_tag_present(skb))
>                         proto = skb->protocol;
> @@ -276,7 +276,8 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
>                                 key_vlan->vlan_id = skb_vlan_tag_get_id(skb);
>                                 key_vlan->vlan_priority =
>                                         (skb_vlan_tag_get_prio(skb) >> VLAN_PRIO_SHIFT);
> -                       } else {
> +                       } else if (proto == cpu_to_be16(ETH_P_8021Q) ||
> +                                               proto == cpu_to_be16(ETH_P_8021AD)) {
>                                 key_vlan->vlan_id = ntohs(vlan->h_vlan_TCI) &
>                                         VLAN_VID_MASK;
>                                 key_vlan->vlan_priority =
> --
> 1.8.3.1
>

It seems there is one similar patch already.
You could refer to https://patchwork.kernel.org/patch/9389565/

Regards
Feng