ACK: [SRU][Xenial][Bionic][Cosmic][PATCH] xfrm: Fix NULL pointer dereference when skb_dst_force clears the dst_entry.

Kleber Souza kleber.souza at canonical.com
Wed Nov 7 08:56:07 UTC 2018


On 11/06/18 15:46, Gavin Guo wrote:
> From: Steffen Klassert <steffen.klassert at secunet.com>
>
> BugLink: https://bugs.launchpad.net/bugs/1801878
>
> Since commit 222d7dbd258d ("net: prevent dst uses after free")
> skb_dst_force() might clear the dst_entry attached to the skb.
> The xfrm code don't expect this to happen, so we crash with
> a NULL pointer dereference in this case. Fix it by checking
> skb_dst(skb) for NULL after skb_dst_force() and drop the packet
> in cast the dst_entry was cleared.
>
> Fixes: 222d7dbd258d ("net: prevent dst uses after free")
> Reported-by: Tobias Hommel <netdev-list at genoetigt.de>
> Reported-by: Kristian Evensen <kristian.evensen at gmail.com>
> Reported-by: Wolfgang Walter <linux at stwm.de>
> Signed-off-by: Steffen Klassert <steffen.klassert at secunet.com>
> (cherry picked from commit 9e1437937807b0122e8da1ca8765be2adca9aee6)
> Signed-off-by: Gavin Guo <gavin.guo at canonical.com>

Acked-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>

> ---
>  net/xfrm/xfrm_output.c | 4 ++++
>  net/xfrm/xfrm_policy.c | 4 ++++
>  2 files changed, 8 insertions(+)
>
> diff --git a/net/xfrm/xfrm_output.c b/net/xfrm/xfrm_output.c
> index 35610cc881a9..c47660fba498 100644
> --- a/net/xfrm/xfrm_output.c
> +++ b/net/xfrm/xfrm_output.c
> @@ -101,6 +101,10 @@ static int xfrm_output_one(struct sk_buff *skb, int err)
>  		spin_unlock_bh(&x->lock);
>  
>  		skb_dst_force(skb);
> +		if (!skb_dst(skb)) {
> +			XFRM_INC_STATS(net, LINUX_MIB_XFRMOUTERROR);
> +			goto error_nolock;
> +		}
>  
>  		if (xfrm_offload(skb)) {
>  			x->type_offload->encap(x, skb);
> diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
> index 7bcd6f1b86a0..1690efebba8a 100644
> --- a/net/xfrm/xfrm_policy.c
> +++ b/net/xfrm/xfrm_policy.c
> @@ -2544,6 +2544,10 @@ int __xfrm_route_forward(struct sk_buff *skb, unsigned short family)
>  	}
>  
>  	skb_dst_force(skb);
> +	if (!skb_dst(skb)) {
> +		XFRM_INC_STATS(net, LINUX_MIB_XFRMFWDHDRERROR);
> +		return 0;
> +	}
>  
>  	dst = xfrm_lookup(net, skb_dst(skb), &fl, NULL, XFRM_LOOKUP_QUEUE);
>  	if (IS_ERR(dst)) {





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