Subject: Re: [PATCH 2/2] xfrm6: fix a potential use after free in xfrm6_policy.c

From: Sergei Shtylyov <[email-masked]>
Date: Mon, 20 Oct 2014 14:36:16 +0400

Hello.

On 10/20/2014 12:49 PM, [email-masked] wrote:

> From: Li RongQing <[email-masked]>

> pskb_may_pull() maybe change skb->data and make nh and exthdr pointer
> oboslete, so recompute the nd and exthdr

> Signed-off-by: Li RongQing <[email-masked]>
> ---
>   net/ipv6/xfrm6_policy.c |   11 ++++++++---
>   1 file changed, 8 insertions(+), 3 deletions(-)

> diff --git a/net/ipv6/xfrm6_policy.c b/net/ipv6/xfrm6_policy.c
> index ac49f84..115fd3b 100644
> --- a/net/ipv6/xfrm6_policy.c
> +++ b/net/ipv6/xfrm6_policy.c
> @@ -170,8 +170,10 @@ _decode_session6(struct sk_buff *skb, struct flowi *fl, int reverse)
>   		case IPPROTO_DCCP:
>   			if (!onlyproto && (nh + offset + 4 < skb->data ||
>   			     pskb_may_pull(skb, nh + offset + 4 - skb->data))) {
> -				__be16 *ports = (__be16 *)exthdr;
> +				__be16 *ports;
>
> +				nh = skb_network_header(skb);
> +				ports = (__be16*)(nh + offset);

    Please insert a space between '__be16' and * like it was done in the 
deleted assignment.

[...]
> @@ -180,8 +182,10 @@ _decode_session6(struct sk_buff *skb, struct flowi *fl, int reverse)
>
>   		case IPPROTO_ICMPV6:
>   			if (!onlyproto && pskb_may_pull(skb, nh + offset + 2 - skb->data)) {
> -				u8 *icmp = (u8 *)exthdr;
> +				u8 *icmp;
>
> +				nh = skb_network_header(skb);
> +				icmp = (u8*)(nh + offset);

    Likewise.

[...]
> @@ -192,8 +196,9 @@ _decode_session6(struct sk_buff *skb, struct flowi *fl, int reverse)
>   		case IPPROTO_MH:
>   			if (!onlyproto && pskb_may_pull(skb, nh + offset + 3 - skb->data)) {
>   				struct ip6_mh *mh;
> -				mh = (struct ip6_mh *)exthdr;
>
> +				nh = skb_network_header(skb);
> +				mh = (struct ip6_mh*)(nh + offset);

    Likewise.

[...]

WBR, Sergei