On 11/23/21 19:48, Jason A. Donenfeld wrote:
From: msizanoen1 <msizanoen@xxxxxxxxxxx>
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
Link: https://bugzilla.kernel.org/show_bug.cgi?id=215105
Fixes: ca7a03c41753 ("ipv6: do not free rt if FIB_LOOKUP_NOREF is set on suppress rule")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
---
The original author of this commit and commit message is anonymous and
is therefore unable to sign off on it. Greg suggested that I do the sign
off, extracting it from the bugzilla entry above, and post it properly.
The patch "seems to work" on first glance, but I haven't looked deeply
at it yet and therefore it doesn't have my Reviewed-by, even though I'm
submitting this patch on the author's behalf. And it should probably get
a good look from the v6 fib folks. The original author should be on this
thread to address issues that come off, and I'll shephard additional
versions that he has.
include/net/fib_rules.h | 4 +++- net/core/fib_rules.c | 2 +- net/ipv4/fib_rules.c | 1 + net/ipv6/fib6_rules.c | 4 ++-- 4 files changed, 7 insertions(+), 4 deletions(-) diff --git a/include/net/fib_rules.h b/include/net/fib_rules.h index 4b10676c69d1..bd07484ab9dd 100644 --- a/include/net/fib_rules.h +++ b/include/net/fib_rules.h @@ -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 diff --git a/net/core/fib_rules.c b/net/core/fib_rules.c index 79df7cd9dbc1..1bb567a3b329 100644 --- a/net/core/fib_rules.c +++ b/net/core/fib_rules.c @@ -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) {diff --git a/net/ipv4/fib_rules.c b/net/ipv4/fib_rules.c index ce54a30c2ef1..364ad3446b2f 100644 --- a/net/ipv4/fib_rules.c +++ b/net/ipv4/fib_rules.c @@ -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; diff --git a/net/ipv6/fib6_rules.c b/net/ipv6/fib6_rules.c index 40f3e4f9f33a..dcedfe29d9d9 100644 --- a/net/ipv6/fib6_rules.c +++ b/net/ipv6/fib6_rules.c @@ -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; }
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