Memory Leak Affecting kernel-default-extra package, versions <5.14.21-150500.55.80.2
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Test your applications- Snyk IDSNYK-SLES155-KERNELDEFAULTEXTRA-8103329
- published28 Sept 2024
- disclosed27 Sept 2024
Introduced: 27 Sep 2024
CVE-2021-47546 (opens in a new tab)How to fix?
Upgrade SLES:15.5 kernel-default-extra to version 5.14.21-150500.55.80.2 or higher.
NVD Description
Note: Versions mentioned in the description apply only to the upstream kernel-default-extra package and not the kernel-default-extra package as distributed by SLES.
See How to fix? for SLES:15.5 relevant fixed versions and status.
In the Linux kernel, the following vulnerability has been resolved:
ipv6: fix memory leak in fib6_rule_suppress
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 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 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_cacheto 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.
References
- https://www.suse.com/security/cve/CVE-2021-47546.html
- https://bugzilla.suse.com/1225504
- https://git.kernel.org/stable/c/209d35ee34e25f9668c404350a1c86d914c54ffa
- https://git.kernel.org/stable/c/8ef8a76a340ebdb2c2eea3f6fb0ebbed09a16383
- https://git.kernel.org/stable/c/cdef485217d30382f3bf6448c54b4401648fe3f1
- https://git.kernel.org/stable/c/ee38eb8cf9a7323884c2b8e0adbbeb2192d31e29