[SRU][F][J][PATCH 2/3] ip: fix triggering of 'icmp redirect'

[Luke Nowakowski-Krijger]

From: Nicolas Dichtel <nicolas.dichtel at 6wind.com>

BugLink: https://bugs.launchpad.net/bugs/1988809

__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 at vger.kernel.org
Fixes: 747c14307214 ("ip: fix dflt addr selection for connected nexthop")
Reported-by: kernel test robot <yujie.liu at intel.com>
Reported-by: Heng Qi <hengqi at linux.alibaba.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel at 6wind.com>
Reviewed-by: David Ahern <dsahern at kernel.org>
Link: https://lore.kernel.org/r/20220829100121.3821-1-nicolas.dichtel@6wind.com
Signed-off-by: Jakub Kicinski <kuba at kernel.org>
(cherry-picked from commit eb55dc09b5dd040232d5de32812cc83001a23da6)
Signed-off-by: Luke Nowakowski-Krijger <luke.nowakowskikrijger at canonical.com>
---
 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 ef3e7a3e3a29e..d38c8ca93ba09 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -399,7 +399,7 @@ 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)
@@ -411,7 +411,7 @@ 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;
 
-- 
2.34.1