On 8/29/22 4:01 AM, Nicolas Dichtel wrote:
> __mkroute_input() uses fib_validate_source() to trigger an icmp redirect.
> My understanding is that fib_validate_source() is used to know if the src
> address and the gateway address are on the same link. For that,
> fib_validate_source() returns 1 (same link) or 0 (not the same network).
> __mkroute_input() is the only user of these positive values, all other
> callers only look if the returned value is negative.
>
> Since the below patch, fib_validate_source() didn't return anymore 1 when
> both addresses are on the same network, because the route lookup returns
> RT_SCOPE_LINK instead of RT_SCOPE_HOST. But this is, in fact, right.
> Let's adapat the test to return 1 again when both addresses are on the same
> link.
>
> CC: stable@xxxxxxxxxxxxxxx
> Fixes: 747c14307214 ("ip: fix dflt addr selection for connected nexthop")
> Reported-by: kernel test robot <yujie.liu@xxxxxxxxx>
> Reported-by: Heng Qi <hengqi@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@xxxxxxxxx>
> ---
>
> This code exists since more than two decades:
> https://git.kernel.org/pub/scm/linux/kernel/git/davem/netdev-vger-cvs.git/commit/?id=0c2c94df8133f
>
> Please, feel free to comment if my analysis seems wrong.
>
> Regards,
> Nicolas
>
> net/ipv4/fib_frontend.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
> index f361d3d56be2..943edf4ad4db 100644
> --- a/net/ipv4/fib_frontend.c
> +++ b/net/ipv4/fib_frontend.c
> @@ -389,7 +389,7 @@ static int __fib_validate_source(struct sk_buff *skb, __be32 src, __be32 dst,
> dev_match = dev_match || (res.type == RTN_LOCAL &&
> dev == net->loopback_dev);
> if (dev_match) {
> - ret = FIB_RES_NHC(res)->nhc_scope >= RT_SCOPE_HOST;
> + ret = FIB_RES_NHC(res)->nhc_scope >= RT_SCOPE_LINK;
> return ret;
> }
> if (no_addr)
> @@ -401,7 +401,7 @@ static int __fib_validate_source(struct sk_buff *skb, __be32 src, __be32 dst,
> ret = 0;
> if (fib_lookup(net, &fl4, &res, FIB_LOOKUP_IGNORE_LINKSTATE) == 0) {
> if (res.type == RTN_UNICAST)
> - ret = FIB_RES_NHC(res)->nhc_scope >= RT_SCOPE_HOST;
> + ret = FIB_RES_NHC(res)->nhc_scope >= RT_SCOPE_LINK;
> }
> return ret;
>
Looks ok to me.
Reviewed-by: David Ahern <dsahern@xxxxxxxxxx>
