netdev - Re: [PATCH] xfrm: Silence warnings triggerable by bad packets

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Message-ID: <CANP3RGfFn30C90M01D+-B7VN9GL5sK8LuiAbP=dJURSHt4WTPw@mail.gmail.com>
Date: Wed, 5 Jul 2023 10:57:04 +0200
From: Maciej Żenczykowski <maze@...gle.com>
To: Herbert Xu <herbert@...dor.apana.org.au>
Cc: Linux Network Development Mailing List <netdev@...r.kernel.org>, Steffen Klassert <steffen.klassert@...unet.com>, 
	Benedict Wong <benedictwong@...gle.com>, Lorenzo Colitti <lorenzo@...gle.com>, 
	Yan Yan <evitayan@...gle.com>
Subject: Re: [PATCH] xfrm: Silence warnings triggerable by bad packets

On Tue, Jul 4, 2023 at 2:54 AM Herbert Xu <herbert@...dor.apana.org.au> wrote:
>
> On Fri, Jun 30, 2023 at 08:37:58AM -0700, Maciej Żenczykowski wrote:
> > Steffan, this isn't of course a patch meant for inclusion, instead just a WARN_ON hit report.
> > The patch is simply what prints the following extra info:
> >
> > xfrm_prepare_input: XFRM_MODE_SKB_CB(skb)->protocol: 17
> > xfrm_inner_mode_encap_remove: x->props.mode: 1 XFRM_MODE_SKB_SB(skb)->protocol:17
> >
> > (note: XFRM_MODE_TUNNEL=1 IPPROTO_UDP=17)
>
> Thanks for the report.  This patch should fix the warnings:
>
> ---8<---
> After the elimination of inner modes, a couple of warnings that
> were previously unreachable can now be triggered by malformed
> inbound packets.
>
> Fix this by:
>
> 1. Moving the setting of skb->protocol into the decap functions.
> 2. Returning -EINVAL when unexpected protocol is seen.
>
> Reported-by: Maciej Żenczykowski<maze@...gle.com>
> Fixes: 5f24f41e8ea6 ("xfrm: Remove inner/outer modes from input path")
> Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
>
> diff --git a/net/xfrm/xfrm_input.c b/net/xfrm/xfrm_input.c
> index 815b38080401..d5ee96789d4b 100644
> --- a/net/xfrm/xfrm_input.c
> +++ b/net/xfrm/xfrm_input.c
> @@ -180,6 +180,8 @@ static int xfrm4_remove_beet_encap(struct xfrm_state *x, struct sk_buff *skb)
>         int optlen = 0;
>         int err = -EINVAL;
>
> +       skb->protocol = htons(ETH_P_IP);
> +
>         if (unlikely(XFRM_MODE_SKB_CB(skb)->protocol == IPPROTO_BEETPH)) {
>                 struct ip_beet_phdr *ph;
>                 int phlen;
> @@ -232,6 +234,8 @@ static int xfrm4_remove_tunnel_encap(struct xfrm_state *x, struct sk_buff *skb)
>  {
>         int err = -EINVAL;
>
> +       skb->protocol = htons(ETH_P_IP);
> +
>         if (!pskb_may_pull(skb, sizeof(struct iphdr)))
>                 goto out;
>
> @@ -267,6 +271,8 @@ static int xfrm6_remove_tunnel_encap(struct xfrm_state *x, struct sk_buff *skb)
>  {
>         int err = -EINVAL;
>
> +       skb->protocol = htons(ETH_P_IPV6);
> +
>         if (!pskb_may_pull(skb, sizeof(struct ipv6hdr)))
>                 goto out;
>
> @@ -296,6 +302,8 @@ static int xfrm6_remove_beet_encap(struct xfrm_state *x, struct sk_buff *skb)
>         int size = sizeof(struct ipv6hdr);
>         int err;
>
> +       skb->protocol = htons(ETH_P_IPV6);
> +
>         err = skb_cow_head(skb, size + skb->mac_len);
>         if (err)
>                 goto out;
> @@ -346,6 +354,7 @@ xfrm_inner_mode_encap_remove(struct xfrm_state *x,
>                         return xfrm6_remove_tunnel_encap(x, skb);
>                 break;
>                 }
> +               return -EINVAL;
>         }
>
>         WARN_ON_ONCE(1);
> @@ -366,19 +375,6 @@ static int xfrm_prepare_input(struct xfrm_state *x, struct sk_buff *skb)
>                 return -EAFNOSUPPORT;
>         }
>
> -       switch (XFRM_MODE_SKB_CB(skb)->protocol) {
> -       case IPPROTO_IPIP:
> -       case IPPROTO_BEETPH:
> -               skb->protocol = htons(ETH_P_IP);
> -               break;
> -       case IPPROTO_IPV6:
> -               skb->protocol = htons(ETH_P_IPV6);
> -               break;
> -       default:
> -               WARN_ON_ONCE(1);
> -               break;
> -       }
> -
>         return xfrm_inner_mode_encap_remove(x, skb);
>  }

Reviewed-by: Maciej Żenczykowski <maze@...gle.com>