[net] ipv4: Don't override return code from ip_route_input_noref()

After ip_route_input() calls ip_route_input_noref(), another
check on skb_dst() is done, but if this fails, we shouldn't
override the return code from ip_route_input_noref(), as it
could have been more specific (i.e. -EHOSTUNREACH).

This also saves one call to skb_dst_force_safe() and one to
skb_dst() in case the ip_route_input_noref() check fails.

Reported-by: Sabrina Dubroca <sdubroca@redhat.com>
Fixes: ad65a2f05695 ("ipv4: call dst_hold_safe() properly")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
 include/net/route.h | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

> After ip_route_input() calls ip_route_input_noref(), another
> check on skb_dst() is done, but if this fails, we shouldn't
> override the return code from ip_route_input_noref(), as it
> could have been more specific (i.e. -EHOSTUNREACH).
>
> This also saves one call to skb_dst_force_safe() and one to
> skb_dst() in case the ip_route_input_noref() check fails.
>
> Reported-by: Sabrina Dubroca <sdubroca@redhat.com>
> Fixes: ad65a2f05695 ("ipv4: call dst_hold_safe() properly")
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Acked-by: Wei Wang <weiwan@google.com>


On Thu, Aug 31, 2017 at 9:11 AM, Stefano Brivio <sbrivio@redhat.com> wrote:
> After ip_route_input() calls ip_route_input_noref(), another
> check on skb_dst() is done, but if this fails, we shouldn't
> override the return code from ip_route_input_noref(), as it
> could have been more specific (i.e. -EHOSTUNREACH).
>
> This also saves one call to skb_dst_force_safe() and one to
> skb_dst() in case the ip_route_input_noref() check fails.
>
> Reported-by: Sabrina Dubroca <sdubroca@redhat.com>
> Fixes: ad65a2f05695 ("ipv4: call dst_hold_safe() properly")
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
> ---
>  include/net/route.h | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/include/net/route.h b/include/net/route.h
> index cb0a76d9dde1..1b09a9368c68 100644
> --- a/include/net/route.h
> +++ b/include/net/route.h
> @@ -189,10 +189,11 @@ static inline int ip_route_input(struct sk_buff *skb, __be32 dst, __be32 src,
>
>         rcu_read_lock();
>         err = ip_route_input_noref(skb, dst, src, tos, devin);
> -       if (!err)
> +       if (!err) {
>                 skb_dst_force_safe(skb);
> -       if (!skb_dst(skb))
> -               err = -EINVAL;
> +               if (!skb_dst(skb))
> +                       err = -EINVAL;
> +       }
>         rcu_read_unlock();
>
>         return err;
> --
> 2.9.4
>

2017-08-31, 18:11:41 +0200, Stefano Brivio wrote:
> After ip_route_input() calls ip_route_input_noref(), another
> check on skb_dst() is done, but if this fails, we shouldn't
> override the return code from ip_route_input_noref(), as it
> could have been more specific (i.e. -EHOSTUNREACH).
> 
> This also saves one call to skb_dst_force_safe() and one to
> skb_dst() in case the ip_route_input_noref() check fails.
> 
> Reported-by: Sabrina Dubroca <sdubroca@redhat.com>
> Fixes: ad65a2f05695 ("ipv4: call dst_hold_safe() properly")

That should be instead:

Fixes: 9df16efadd2a ("ipv4: call dst_hold_safe() properly")

Acked-by: Sabrina Dubroca <sd@queasysnail.net>

From: Sabrina Dubroca <sd@queasysnail.net>
Date: Fri, 1 Sep 2017 01:45:06 +0200

> 2017-08-31, 18:11:41 +0200, Stefano Brivio wrote:
>> After ip_route_input() calls ip_route_input_noref(), another
>> check on skb_dst() is done, but if this fails, we shouldn't
>> override the return code from ip_route_input_noref(), as it
>> could have been more specific (i.e. -EHOSTUNREACH).
>> 
>> This also saves one call to skb_dst_force_safe() and one to
>> skb_dst() in case the ip_route_input_noref() check fails.
>> 
>> Reported-by: Sabrina Dubroca <sdubroca@redhat.com>
>> Fixes: ad65a2f05695 ("ipv4: call dst_hold_safe() properly")
> 
> That should be instead:
> 
> Fixes: 9df16efadd2a ("ipv4: call dst_hold_safe() properly")
> 
> Acked-by: Sabrina Dubroca <sd@queasysnail.net>

Applied with fixed Fixes: tag, thanks.