[PATCH net] ipv4: Handle attempt to delete multipath route when fib_info contains an nh reference

[David Ahern <dsahern@kernel.org>]

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")
Reported-by: Gwangun Jung <exsociety@gmail.com>
Signed-off-by: David Ahern <dsahern@kernel.org>
---
 net/ipv4/fib_semantics.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 2dc97583d279..17caa73f57e6 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -926,6 +926,10 @@ int fib_nh_match(struct net *net, struct fib_config *cfg, struct fib_info *fi,
 	if (!cfg->fc_mp)
 		return 0;
 
+	/* multipath spec and nexthop id are mutually exclusive */
+	if (fi->nh)
+		return 1;
+
 	rtnh = cfg->fc_mp;
 	remaining = cfg->fc_mp_len;
 
-- 
2.25.1