Commit ee38eb8c authored Nov 23, 2021 by msizanoen1 Committed by Greg Kroah-Hartman Dec 08, 2021

ipv6: fix memory leak in fib6_rule_suppress

commit cdef485217d30382f3bf6448c54b4401648fe3f1 upstream.

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: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 9d159628

include/net/fib_rules.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -68,7 +68,7 @@ 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);

net/core/fib_rules.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -300,7 +300,7 @@ int fib_rules_lookup(struct fib_rules_ops ops, struct flowi fl,
		else
		err = ops->action(rule, fl, flags, arg);

		if (!err && ops->suppress && ops->suppress(rule, arg))
		if (!err && ops->suppress && ops->suppress(rule, flags, arg))
		continue;

		if (err != -EAGAIN) {

net/ipv4/fib_rules.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -137,7 +137,7 @@ static int fib4_rule_action(struct fib_rule rule, struct flowi flp,
		return err;
		}

		static bool fib4_rule_suppress(struct fib_rule rule, struct fib_lookup_arg arg)
		static bool fib4_rule_suppress(struct fib_rule rule, int flags, struct fib_lookup_arg arg)
		{
		struct fib_result result = (struct fib_result ) arg->result;
		struct net_device *dev = NULL;

net/ipv6/fib6_rules.c

+2 −3

Original line number	Diff line number	Diff line
		@@ -260,7 +260,7 @@ static int fib6_rule_action(struct fib_rule rule, struct flowi flp,
		return __fib6_rule_action(rule, flp, flags, arg);
		}

		static bool fib6_rule_suppress(struct fib_rule rule, struct fib_lookup_arg arg)
		static bool fib6_rule_suppress(struct fib_rule rule, int flags, struct fib_lookup_arg arg)
		{
		struct fib6_result *res = arg->result;
		struct rt6_info *rt = res->rt6;
		@@ -287,8 +287,7 @@ static bool fib6_rule_suppress(struct fib_rule rule, struct fib_lookup_arg arg
		return false;

		suppress_route:
		if (!(arg->flags & FIB_LOOKUP_NOREF))
		ip6_rt_put(rt);
		ip6_rt_put_flags(rt, flags);
		return true;
		}