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@vger.kernel.org Fixes: 747c14307214 ("ip: fix dflt addr selection for connected nexthop") Reported-by: kernel test robot yujie.liu@intel.com Reported-by: Heng Qi hengqi@linux.alibaba.com Signed-off-by: Nicolas Dichtel nicolas.dichtel@6wind.com

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This code exists since more than two decades: https://git.kernel.org/pub/scm/linux/kernel/git/davem/netdev-vger-cvs.git/co...

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@kernel.org