Commit cdef4852 authored by msizanoen1's avatar msizanoen1 Committed by David S. Miller
Browse files

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 ca7a03c4 ("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

Link: https://bugzilla.kernel.org/show_bug.cgi?id=215105


Fixes: ca7a03c4 ("ipv6: do not free rt if FIB_LOOKUP_NOREF is set on suppress rule")
Cc: stable@vger.kernel.org
Signed-off-by: default avatarJason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent d00a50cf

include/net/fib_rules.h

+3 −1
Original line number Diff line number Diff line
@@ -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

net/core/fib_rules.c

+1 −1
Original line number Diff line number Diff line
@@ -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) {

net/ipv4/fib_rules.c

+1 −0
Original line number Diff line number Diff line
@@ -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;

net/ipv6/fib6_rules.c

+2 −2
Original line number Diff line number Diff line
@@ -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;

}