Re: [PATCH net-next v2 1/7] net: ip: make fib_validate_source() return drop reason

[Menglong Dong]

On Thu, Oct 10, 2024 at 4:25 PM Paolo Abeni <pabeni@xxxxxxxxxx> wrote:
>
>
>
> On 10/7/24 09:46, Menglong Dong wrote:
> > In this commit, we make fib_validate_source/__fib_validate_source return
> > -reason instead of errno on error. As the return value of them can be
> > -errno, 0, and 1, we can't make it return enum skb_drop_reason directly.
> >
> > In the origin logic, if __fib_validate_source() return -EXDEV,
> > LINUX_MIB_IPRPFILTER will be counted. And now, we need to adjust it by
> > checking "reason == SKB_DROP_REASON_IP_RPFILTER". However, this will take
> > effect only after the patch "net: ip: make ip_route_input_noref() return
> > drop reasons", as we can't pass the drop reasons from
> > fib_validate_source() to ip_rcv_finish_core() in this patch.
> >
> > We set the errno to -EINVAL when fib_validate_source() is called and the
> > validation fails, as the errno can be checked in the caller and now its
> > value is -reason, which can lead misunderstand.
> >
> > Following new drop reasons are added in this patch:
> >
> >    SKB_DROP_REASON_IP_LOCAL_SOURCE
> >    SKB_DROP_REASON_IP_INVALID_SOURCE
> >
> > Signed-off-by: Menglong Dong <dongml2@xxxxxxxxxxxxxxx>
>
> Looking at the next patches, I'm under the impression that the overall
> code will be simpler if you let __fib_validate_source() return directly
> a drop reason, and fib_validate_source(), too. Hard to be sure without
> actually do the attempt... did you try such patch by any chance?
>

I analysed the usages of fib_validate_source() before. The
return value of fib_validate_source() can be -errno, "0", and "1".
And the value "1" can be used by the caller, such as
__mkroute_input(). Making it return drop reasons can't cover this
case.

It seems that __mkroute_input() is the only case that uses the
positive returning value of fib_validate_source(). Let me think
about it more in this case.

Thanks!
Menglong Dong

> Thanks!
>
> Paolo
>