RE: [PATCH net v2] ipv4: Fix potential uninit variable access buf in __ip_make_skb()

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Ziyang Xuan wrote:
> Like commit ea30388baebc ("ipv6: Fix an uninit variable access bug in
> __ip6_make_skb()"). icmphdr does not in skb linear region under the
> scenario of SOCK_RAW socket. Access icmp_hdr(skb)->type directly will
> trigger the uninit variable access bug.
> 
> Use a local variable icmp_type to carry the correct value in different
> scenarios.
> 
> Fixes: 96793b482540 ("[IPV4]: Add ICMPMsgStats MIB (RFC 4293)")
> Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
> ---
> v2:
>   - Use sk->sk_type not sk->sk_socket->type.

This is reached through

  raw_sendmsg
    raw_probe_proto_opt
    ip_push_pending_frames
      ip_finish_skb
        __ip_make_skb

At this point, the icmp header has already been copied into skb linear
area. Is the isue that icmp_hdr/skb_transport_header is not set in
this path? 

> ---
>  net/ipv4/ip_output.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
> index 4e4e308c3230..21507c9ce0fc 100644
> --- a/net/ipv4/ip_output.c
> +++ b/net/ipv4/ip_output.c
> @@ -1570,9 +1570,15 @@ struct sk_buff *__ip_make_skb(struct sock *sk,
>  	cork->dst = NULL;
>  	skb_dst_set(skb, &rt->dst);
>  
> -	if (iph->protocol == IPPROTO_ICMP)
> -		icmp_out_count(net, ((struct icmphdr *)
> -			skb_transport_header(skb))->type);
> +	if (iph->protocol == IPPROTO_ICMP) {
> +		u8 icmp_type;
> +
> +		if (sk->sk_type == SOCK_RAW && !inet_sk(sk)->hdrincl)
> +			icmp_type = fl4->fl4_icmp_type;
> +		else
> +			icmp_type = icmp_hdr(skb)->type;
> +		icmp_out_count(net, icmp_type);
> +	}
>  
>  	ip_cork_release(cork);
>  out:
> -- 
> 2.25.1
>