Re: [PATCH net] fix null-deref in ipv4_link_failure

[Paolo Abeni <pabeni@redhat.com>]

On Thu, 2023-09-07 at 20:18 -0700, Kyle Zeng wrote:
> Currently, we assume the skb is associated with a device before calling
> __ip_options_compile, which is not always the case if it is re-routed by
> ipvs.
> When skb->dev is NULL, dev_net(skb->dev) will become null-dereference.
> This patch adds a check for the edge case and switch to use the net_device
> from the rtable when skb->dev is NULL.
> 
> Suggested-by: Paolo Abeni<pabeni@redhat.com>
> Suggested-by: David Ahern <dsahern@kernel.org>
> Signed-off-by: Kyle Zeng <zengyhkyle@gmail.com>
> Cc: Stephen Suryaputra <ssuryaextr@gmail.com>
> ---
>  net/ipv4/route.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
> index d8c99bdc617..1be34e5eea1 100644
> --- a/net/ipv4/route.c
> +++ b/net/ipv4/route.c
> @@ -1214,6 +1214,7 @@ EXPORT_INDIRECT_CALLABLE(ipv4_dst_check);
>  static void ipv4_send_dest_unreach(struct sk_buff *skb)
>  {
>  	struct ip_options opt;
> +	struct net_device *dev;
>  	int res;
>  
>  	/* Recompile ip options since IPCB may not be valid anymore.
> @@ -1230,7 +1231,8 @@ static void ipv4_send_dest_unreach(struct sk_buff *skb)
>  		opt.optlen = ip_hdr(skb)->ihl * 4 - sizeof(struct iphdr);
>  
>  		rcu_read_lock();
> -		res = __ip_options_compile(dev_net(skb->dev), &opt, skb, NULL);
> +		dev = skb->dev ? skb->dev : skb_rtable(skb)->dst.dev;
> +		res = __ip_options_compile(dev_net(dev), &opt, skb, NULL);
>  		rcu_read_unlock();
>  
>  		if (res)

The patch LGTM, but if you are going to re-post to address Vadim's
feedback, please additionally drop my Suggested-by. I only reviewed a
previous revision.

Thanks!

Paolo