netdev - Re: [PATCH 1/2 net] 6lowpan: add missing pskb_may

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Date:	Thu, 10 May 2012 18:05:46 +0400
From:	Alexander Smirnov <alex.bluesman.smirnov@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH 1/2 net] 6lowpan: add missing pskb_may_pull() check

Hi Eric,

2012/5/10 Eric Dumazet <eric.dumazet@...il.com>:
> On Thu, 2012-05-10 at 17:22 +0400, alex.bluesman.smirnov@...il.com
> wrote:
>> From: Alexander Smirnov <alex.bluesman.smirnov@...il.com>
>>
>> Add pskb_may_pull() call when fetching u8 from skb.
>>
>> Signed-off-by: Alexander Smirnov <alex.bluesman.smirnov@...il.com>
>> ---
>>  net/ieee802154/6lowpan.c |    2 ++
>>  1 files changed, 2 insertions(+), 0 deletions(-)
>>
>> diff --git a/net/ieee802154/6lowpan.c b/net/ieee802154/6lowpan.c
>> index 32eb417..0ab3efe 100644
>> --- a/net/ieee802154/6lowpan.c
>> +++ b/net/ieee802154/6lowpan.c
>> @@ -295,6 +295,8 @@ static u8 lowpan_fetch_skb_u8(struct sk_buff *skb)
>>  {
>>       u8 ret;
>>
>> +     BUG_ON(!pskb_may_pull(skb, 1));
>> +
>>       ret = skb->data[0];
>>       skb_pull(skb, 1);
>>
>
> No, you cant do that.
>
> pskb_may_pull() can fail, and you crash your machine instead of graceful
> error reporting.
>

thanks for the comment!

Using BUG() macro I just want to indicate that something in the bottom
of the stack went terribly wrong and you must check your code for
bugs..

>
>
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