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.
Hello Willem,

Does my answer answer your doubts?

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
>>>
>>
>>
>> .
>>
> 
> .
>