From: David Ahern <dsahern@gmail.com>
To: msizanoen <msizanoen@qtmlabs.xyz>,
davem@davemloft.net, yoshfuji@linux-ipv6.org, dsahern@kernel.org,
kuba@kernel.org
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: Kernel leaks memory in ip6_dst_cache when suppress_prefix is present in ipv6 routing rules and a `fib` rule is present in ipv6 nftables rules
Date: Fri, 29 Oct 2021 17:53:03 -0600 [thread overview]
Message-ID: <9015da81-689a-5ff6-c5ca-55c28dec1867@gmail.com> (raw)
In-Reply-To: <e022d597-302d-c061-0830-6ed20aa61e56@qtmlabs.xyz>
On 10/26/21 8:24 AM, msizanoen wrote:
> 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 this commit:
> https://github.com/torvalds/linux/commit/ca7a03c4175366a92cee0ccc4fec0038c3266e26
>
>
> The problem with that patch is that the generic args->flags always have
> FIB_LOOKUP_NOREF set[1][2] but the
> ip6-specific flag RT6_LOOKUP_F_DST_NOREF might not be specified, leading
> to fib6_rule_suppress not
> decreasing the refcount when needed. This can be fixed by exposing 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.
>
> How to reproduce:
> - Add the following nftables rule to a prerouting chain: `meta nfproto
> ipv6 fib saddr . mark . iif oif missing drop`
exact command? I have not played with nftables. Do you have a stack
trace of where the dst reference is getting taken?
> - Run `sudo ip -6 rule add table main suppress_prefixlength 0`
> - Watch `sudo slabtop -o | grep ip6_dst_cache` memory usage increase
> with every incoming ipv6 packet
>
> Example
> patch:https://gist.github.com/msizanoen1/36a2853467a9bd34fadc5bb3783fde0f
>
> [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
>
>
>
next prev parent reply other threads:[~2021-10-29 23:53 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-26 14:24 Kernel leaks memory in ip6_dst_cache when suppress_prefix is present in ipv6 routing rules and a `fib` rule is present in ipv6 nftables rules msizanoen
2021-10-29 23:53 ` David Ahern [this message]
2021-10-30 0:25 ` msizanoen
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