Re: [PATCH 1/2 net] 6lowpan: add missing pskb_may_pull() check

[Eric Dumazet <eric.dumazet@gmail.com>]

On Thu, 2012-05-10 at 17:22 +0400, alex.bluesman.smirnov@gmail.com
wrote:
> From: Alexander Smirnov <alex.bluesman.smirnov@gmail.com>
> 
> Add pskb_may_pull() call when fetching u8 from skb.
> 
> Signed-off-by: Alexander Smirnov <alex.bluesman.smirnov@gmail.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.