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

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

Ziyang Xuan (William) wrote:
> >> 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? 
> >>
> > Hello Willem,
> > 
> > raw_sendmsg
> >   ip_append_data(..., transhdrlen==0, ...) // !inet->hdrincl
> > 
> > Parameter "transhdrlen" of ip_append_data() equals to 0 in raw_sendmsg()
> > not sizeof(struct icmphdr) as in ping_v4_sendmsg().
> > 
> > William Xuan.
> Hello Willem,
> 
> Does my answer answer your doubts?

Thanks. Yes, that explains. Would you mind adding a comment to that
effect. Sommething like

    /* for such sockets, transport hlen is zero and icmp_hdr incorrect */
    if (sk->sk_type == SOCK_RAW && !inet_sk(sk)->hdrincl)

I missed your previous response, William. Sorry about that.
 
> William Xuan
> >>> ---
> >>>  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
> >>>
> >>
> >>
> >> .
> >>
> > 
> > .
> >