CVE-2021-47546 (GCVE-0-2021-47546)

Vulnerability from cvelistv5 – Published: 2024-05-24 15:09 – Updated: 2025-05-04 12:41
VLAI?
Title
ipv6: fix memory leak in fib6_rule_suppress
Summary
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` 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
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: ca7a03c4175366a92cee0ccc4fec0038c3266e26 , < ee38eb8cf9a7323884c2b8e0adbbeb2192d31e29 (git)
Affected: ca7a03c4175366a92cee0ccc4fec0038c3266e26 , < 209d35ee34e25f9668c404350a1c86d914c54ffa (git)
Affected: ca7a03c4175366a92cee0ccc4fec0038c3266e26 , < 8ef8a76a340ebdb2c2eea3f6fb0ebbed09a16383 (git)
Affected: ca7a03c4175366a92cee0ccc4fec0038c3266e26 , < cdef485217d30382f3bf6448c54b4401648fe3f1 (git)
Affected: d37c966752043733eb847dd897d6e3405084c559 (git)
Affected: ecc265624956ea784cb2bd2b31a95bd54c4f5f13 (git)
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    Linux Linux Affected: 5.4
Unaffected: 0 , < 5.4 (semver)
Unaffected: 5.4.164 , ≤ 5.4.* (semver)
Unaffected: 5.10.84 , ≤ 5.10.* (semver)
Unaffected: 5.15.7 , ≤ 5.15.* (semver)
Unaffected: 5.16 , ≤ * (original_commit_for_fix)
Create a notification for this product.
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