In the Linux kernel, the following vulnerability has been resolved:
ipv6: fix memory leak in fib6rulesuppress
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
FIBLOOKUPNOREF is set on suppress rule").
The problem with that change is that the generic args->flags
always have
FIB_LOOKUP_NOREF
set1 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 testchain '{ type filter hook prerouting priority filter + 10; policy accept; }'
sudo nft add rule inet test testchain 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 RT6LOOKUPFDSTNOREF instead of the generic
FIBLOOKUPNOREF when decreasing the refcount, like this.