FAILED: patch "[PATCH] ipv6: fix memory leak in fib6_rule_suppress" failed to apply to 5.4-stable tree

The patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From cdef485217d30382f3bf6448c54b4401648fe3f1 Mon Sep 17 00:00:00 2001
From: msizanoen1 <[email protected]>
Date: Tue, 23 Nov 2021 13:48:32 +0100
Subject: [PATCH] ipv6: fix memory leak in fib6_rule_suppress

The kernel leaks memory when a fib rule is present in IPv6 nftables firewall rules and a suppress_prefix rule is present in the IPv6 routing rules (used by certain tools such as wg-quick). In such scenarios, every incoming packet will leak an allocation in ip6_dst_cache slab cache.

After some hours of bpftrace-ing and source code reading, I tracked down the issue to ca7a03c41753 ("ipv6: do not free rt if FIB_LOOKUP_NOREF is set on suppress rule").

The problem with that change is that the generic args->flags always have FIB_LOOKUP_NOREF set[1][2] but the IPv6-specific flag RT6_LOOKUP_F_DST_NOREF might not be, leading to fib6_rule_suppress not decreasing the refcount when needed.

How to reproduce:
- Add the following nftables rule to a prerouting chain:
meta nfproto ipv6 fib saddr . mark . iif oif missing drop
This can be done with:
sudo nft create table inet test
sudo nft create chain inet test test_chain '{ type filter hook prerouting priority filter + 10; policy accept; }' sudo nft add rule inet test test_chain meta nfproto ipv6 fib saddr . mark . iif oif missing drop
- Run:
sudo ip -6 rule add table main suppress_prefixlength 0
- Watch sudo slabtop -o | grep ip6_dst_cache to see memory usage increase
with every incoming ipv6 packet.

This patch exposes the protocol-specific flags to the protocol specific suppress function, and check the protocol-specific flags argument for RT6_LOOKUP_F_DST_NOREF instead of the generic FIB_LOOKUP_NOREF when decreasing the refcount, like this.

[1]: https://github.com/torvalds/linux/blob/ca7a03c4175366a92cee0ccc4fec0038c3266e26/net/ipv6/fib6_rules.c#L71
[2]: https://github.com/torvalds/linux/blob/ca7a03c4175366a92cee0ccc4fec0038c3266e26/net/ipv6/fib6_rules.c#L99

index 4b10676c69d1..bd07484ab9dd 100644
@@ -69,7 +69,7 @@ struct fib_rules_ops {
 	int			(*action)(struct fib_rule *,
 					  struct flowi *, int,
 					  struct fib_lookup_arg *);
-	bool			(*suppress)(struct fib_rule *,
+	bool			(*suppress)(struct fib_rule *, int,
 					    struct fib_lookup_arg *);
 	int			(*match)(struct fib_rule *,
 					 struct flowi *, int);

@@ -218,7 +218,9 @@ INDIRECT_CALLABLE_DECLARE(int fib4_rule_action(struct fib_rule *rule,
 			    struct fib_lookup_arg *arg));
 
 INDIRECT_CALLABLE_DECLARE(bool fib6_rule_suppress(struct fib_rule *rule,
+						int flags,
 						struct fib_lookup_arg *arg));
 INDIRECT_CALLABLE_DECLARE(bool fib4_rule_suppress(struct fib_rule *rule,
+						int flags,
 						struct fib_lookup_arg *arg));
 #endif

index 79df7cd9dbc1..1bb567a3b329 100644
@@ -323,7 +323,7 @@ int fib_rules_lookup(struct fib_rules_ops *ops, struct flowi *fl,
 		if (!err && ops->suppress && INDIRECT_CALL_MT(ops->suppress,
 							      fib6_rule_suppress,
 							      fib4_rule_suppress,
-							      rule, arg))
+							      rule, flags, arg))
 			continue;
 
 		if (err != -EAGAIN) {

index ce54a30c2ef1..364ad3446b2f 100644
@@ -141,6 +141,7 @@ INDIRECT_CALLABLE_SCOPE int fib4_rule_action(struct fib_rule *rule,
 }
 
 INDIRECT_CALLABLE_SCOPE bool fib4_rule_suppress(struct fib_rule *rule,
+						int flags,
 						struct fib_lookup_arg *arg)
 {
 	struct fib_result *result = (struct fib_result *) arg->result;

index 40f3e4f9f33a..dcedfe29d9d9 100644
@@ -267,6 +267,7 @@ INDIRECT_CALLABLE_SCOPE int fib6_rule_action(struct fib_rule *rule,
 }
 
 INDIRECT_CALLABLE_SCOPE bool fib6_rule_suppress(struct fib_rule *rule,
+						int flags,
 						struct fib_lookup_arg *arg)
 {
 	struct fib6_result *res = arg->result;

@@ -294,8 +295,7 @@ INDIRECT_CALLABLE_SCOPE bool fib6_rule_suppress(struct fib_rule *rule,
 	return false;
 
 suppress_route:
-	if (!(arg->flags & FIB_LOOKUP_NOREF))
-		ip6_rt_put(rt);
+	ip6_rt_put_flags(rt, flags);
 	return true;
 }