Re: [PATCH net] ipv6: Fix return value of ipv6_mc_may_pull() for malformed packets

[Guillaume Nault <gnault@redhat.com>]

On Tue, Aug 13, 2019 at 12:46:01AM +0200, Stefano Brivio wrote:
> Commit ba5ea614622d ("bridge: simplify ip_mc_check_igmp() and
> ipv6_mc_check_mld() calls") replaces direct calls to pskb_may_pull()
> in br_ipv6_multicast_mld2_report() with calls to ipv6_mc_may_pull(),
> that returns -EINVAL on buffers too short to be valid IPv6 packets,
> while maintaining the previous handling of the return code.
> 
> This leads to the direct opposite of the intended effect: if the
> packet is malformed, -EINVAL evaluates as true, and we'll happily
> proceed with the processing.
> 
> Return 0 if the packet is too short, in the same way as this was
> fixed for IPv4 by commit 083b78a9ed64 ("ip: fix ip_mc_may_pull()
> return value").
> 
> I don't have a reproducer for this, unlike the one referred to by
> the IPv4 commit, but this is clearly broken.
> 
> Fixes: ba5ea614622d ("bridge: simplify ip_mc_check_igmp() and ipv6_mc_check_mld() calls")
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
> ---
>  include/net/addrconf.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/net/addrconf.h b/include/net/addrconf.h
> index becdad576859..3f62b347b04a 100644
> --- a/include/net/addrconf.h
> +++ b/include/net/addrconf.h
> @@ -206,7 +206,7 @@ static inline int ipv6_mc_may_pull(struct sk_buff *skb,
>  				   unsigned int len)
>  {
>  	if (skb_transport_offset(skb) + ipv6_transport_len(skb) < len)
> -		return -EINVAL;
> +		return 0;
>  
>  	return pskb_may_pull(skb, len);
>  }

Acked-by: Guillaume Nault <gnault@redhat.com>