On Tue, Nov 23, 2021 at 01:48:32PM +0100, msizanoen1 wrote:
> 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 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>
> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> ---
> This is a backport of the patch to the 5.4 LTS kernels.
Wonderful, now queued up, thanks!
greg k-h
