netdev - Re: [PATCH net] ipv4: Fix potential uninit variable access buf in __ip_make

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Date:   Thu, 6 Apr 2023 12:06:58 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Ziyang Xuan <william.xuanziyang@...wei.com>
Cc:     davem@...emloft.net, dsahern@...nel.org, kuba@...nel.org,
        pabeni@...hat.com, netdev@...r.kernel.org, dlstevens@...ibm.com
Subject: Re: [PATCH net] ipv4: Fix potential uninit variable access buf in __ip_make_skb()

On Thu, Apr 6, 2023 at 5:11 AM Ziyang Xuan
<william.xuanziyang@...wei.com> 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@...wei.com>
> ---
>  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..57921b297a8e 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_socket->type == SOCK_RAW && !inet_sk(sk)->hdrincl)

What is the reason for not using sk->sk_type ?

> +                       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
>