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

Willem de Bruijn
2023-04-10T14:30:35Z

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
>