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

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Date:   Thu, 27 Oct 2016 13:53:30 +0800
From:   zhong jiang <zhongjiang@...wei.com>
To:     Gao Feng <fgao@...ai8.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 2016/10/27 12:02, Gao Feng wrote:
> 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
>
> .
>
 sorry, I doesn't notice that patch.

 Thanks
 zhongjiang