netdev - Re: [PATCH net v2 1/2] net: do not keep the dst cache when uncloning an skb dst and its metadata

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Message-ID: <42c623d9dc86399f62bef9bbe40b38aa7143a41b.camel@redhat.com>
Date:   Mon, 07 Feb 2022 19:17:07 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Antoine Tenart <atenart@...nel.org>, davem@...emloft.net,
        kuba@...nel.org
Cc:     netdev@...r.kernel.org, vladbu@...dia.com, pshelar@....org,
        daniel@...earbox.net
Subject: Re: [PATCH net v2 1/2] net: do not keep the dst cache when
 uncloning an skb dst and its metadata

On Mon, 2022-02-07 at 18:13 +0100, Antoine Tenart wrote:
> When uncloning an skb dst and its associated metadata a new dst+metadata
> is allocated and the tunnel information from the old metadata is copied
> over there.
> 
> The issue is the tunnel metadata has references to cached dst, which are
> copied along the way. When a dst+metadata refcount drops to 0 the
> metadata is freed including the cached dst entries. As they are also
> referenced in the initial dst+metadata, this ends up in UaFs.
> 
> In practice the above did not happen because of another issue, the
> dst+metadata was never freed because its refcount never dropped to 0
> (this will be fixed in a subsequent patch).
> 
> Fix this by initializing the dst cache after copying the tunnel
> information from the old metadata to also unshare the dst cache.
> 
> Fixes: d71785ffc7e7 ("net: add dst_cache to ovs vxlan lwtunnel")
> Cc: Paolo Abeni <pabeni@...hat.com>
> Reported-by: Vlad Buslov <vladbu@...dia.com>
> Tested-by: Vlad Buslov <vladbu@...dia.com>
> Signed-off-by: Antoine Tenart <atenart@...nel.org>
> ---
>  include/net/dst_metadata.h | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/include/net/dst_metadata.h b/include/net/dst_metadata.h
> index 14efa0ded75d..b997e0c1e362 100644
> --- a/include/net/dst_metadata.h
> +++ b/include/net/dst_metadata.h
> @@ -123,6 +123,19 @@ static inline struct metadata_dst *tun_dst_unclone(struct sk_buff *skb)
>  
>  	memcpy(&new_md->u.tun_info, &md_dst->u.tun_info,
>  	       sizeof(struct ip_tunnel_info) + md_size);
> +#ifdef CONFIG_DST_CACHE
> +	/* Unclone the dst cache if there is one */
> +	if (new_md->u.tun_info.dst_cache.cache) {
> +		int ret;
> +
> +		ret = dst_cache_init(&new_md->u.tun_info.dst_cache, GFP_ATOMIC);
> +		if (ret) {
> +			metadata_dst_free(new_md);
> +			return ERR_PTR(ret);
> +		}
> +	}
> +#endif
> +
>  	skb_dst_drop(skb);
>  	dst_hold(&new_md->dst);
>  	skb_dst_set(skb, &new_md->dst);

LGTM, thanks!

Acked-by: Paolo Abeni <pabeni@...hat.com>