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

["Ziyang Xuan (William)" <william.xuanziyang@huawei.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? 
> 
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.
>> ---
>>  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
>>
> 
> 
> .
>