[PATCH linux-next] ipv4: Fix NULL deference in fnhe_remove_oldest()

Coverity complains that linux-next commit 67d6d681e15b5 ("ipv4: make
exception cache less predictible") neglected to check for NULL before
dereferencing 'oldest'. It appears to be possible to fall through the for
loop without ever setting 'oldest'.

Cc: Eric Dumazet <edumazet@google.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Hideaki YOSHIFUJI <redacted>
Cc: David Ahern <dsahern@kernel.org>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Tim Gardner <redacted>
---
 net/ipv4/route.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index d6899ab5fb39..e85026591a09 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c

@@ -603,9 +603,11 @@ static void fnhe_remove_oldest(struct fnhe_hash_bucket *hash)
 			oldest_p = fnhe_p;
 		}
 	}
-	fnhe_flush_routes(oldest);
-	*oldest_p = oldest->fnhe_next;
-	kfree_rcu(oldest, rcu);
+	if (oldest) {
+		fnhe_flush_routes(oldest);
+		*oldest_p = oldest->fnhe_next;
+		kfree_rcu(oldest, rcu);
+	}
 }
 
 static u32 fnhe_hashfun(__be32 daddr)

-- 
2.33.0