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Date:   Thu,  6 Oct 2022 10:48:49 -0600
From:   David Ahern <>
        David Ahern <>,
        Gwangun Jung <>
Subject: [PATCH v3 net] ipv4: Handle attempt to delete multipath route when fib_info contains an nh reference

Gwangun Jung reported a slab-out-of-bounds access in fib_nh_match:
    fib_nh_match+0xf98/0x1130 linux-6.0-rc7/net/ipv4/fib_semantics.c:961
    fib_table_delete+0x5f3/0xa40 linux-6.0-rc7/net/ipv4/fib_trie.c:1753
    inet_rtm_delroute+0x2b3/0x380 linux-6.0-rc7/net/ipv4/fib_frontend.c:874

Separate nexthop objects are mutually exclusive with the legacy
multipath spec. Fix fib_nh_match to return if the config for the
to be deleted route contains a multipath spec while the fib_info
is using a nexthop object.

Fixes: 493ced1ac47c ("ipv4: Allow routes to use nexthop objects")
Fixes: 6bf92d70e690 ("net: ipv4: fix route with nexthop object delete warning")
Reported-by: Gwangun Jung <>
Signed-off-by: David Ahern <>
- removed nh check in multipath; forgot to remove it in v2
- fixed expected return code on selftest

- moved the fi->nh check up and added second Fixes tag (Ido's comments)

 net/ipv4/fib_semantics.c                    | 8 ++++----
 tools/testing/selftests/net/ | 5 +++++
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 2dc97583d279..e9a7f70a54df 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -888,13 +888,13 @@ int fib_nh_match(struct net *net, struct fib_config *cfg, struct fib_info *fi,
 		return 1;
+	/* cannot match on nexthop object attributes */
+	if (fi->nh)
+		return 1;
 	if (cfg->fc_oif || cfg->fc_gw_family) {
 		struct fib_nh *nh;
-		/* cannot match on nexthop object attributes */
-		if (fi->nh)
-			return 1;
 		nh = fib_info_nh(fi, 0);
 		if (cfg->fc_encap) {
 			if (fib_encap_match(net, cfg->fc_encap_type,
diff --git a/tools/testing/selftests/net/ b/tools/testing/selftests/net/
index d5a0dd548989..ee5e98204d3d 100755
--- a/tools/testing/selftests/net/
+++ b/tools/testing/selftests/net/
@@ -1223,6 +1223,11 @@ ipv4_fcnal()
 	log_test $rc 0 "Delete nexthop route warning"
 	run_cmd "$IP route delete nhid 12"
 	run_cmd "$IP nexthop del id 12"
+	run_cmd "$IP nexthop add id 21 via dev veth1"
+	run_cmd "$IP ro add nhid 21"
+	run_cmd "$IP ro del nexthop via dev veth1 nexthop via dev veth1"
+	log_test $? 2 "Delete multipath route with only nh id based entry"

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