cbcvebase.
CVE-2021-47546
published 2024-05-24

CVE-2021-47546: 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…

PriorityP421medium5.5CVSS 3.1
AVLACLPRLUINSUCNINAH
EPSS
0.22%
12.9th percentile
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

Affected

17 ranges
VendorProductVersion rangeFixed in
debianlinux< linux 5.15.15-1 (bookworm)linux 5.15.15-1 (bookworm)
linuxlinux——
linuxlinux——
linuxlinux——
linuxlinux>= 5.2.19 < 5.35.3
linuxlinux>= 5.3.4 < 5.45.4
linuxlinux>= ca7a03c4175366a92cee0ccc4fec0038c3266e26 < ee38eb8cf9a7323884c2b8e0adbbeb2192d31e29ee38eb8cf9a7323884c2b8e0adbbeb2192d31e29
linuxlinux>= ca7a03c4175366a92cee0ccc4fec0038c3266e26 < 209d35ee34e25f9668c404350a1c86d914c54ffa209d35ee34e25f9668c404350a1c86d914c54ffa
linuxlinux>= ca7a03c4175366a92cee0ccc4fec0038c3266e26 < 8ef8a76a340ebdb2c2eea3f6fb0ebbed09a163838ef8a76a340ebdb2c2eea3f6fb0ebbed09a16383
linuxlinux>= ca7a03c4175366a92cee0ccc4fec0038c3266e26 < cdef485217d30382f3bf6448c54b4401648fe3f1cdef485217d30382f3bf6448c54b4401648fe3f1
linuxlinux_kernel>= 0 < 5.10.84-15.10.84-1
linuxlinux_kernel>= 0 < 5.15.15-15.15.15-1
linuxlinux_kernel>= 0 < 5.15.15-15.15.15-1
linuxlinux_kernel>= 0 < 5.15.15-15.15.15-1
linuxlinux_kernel>= 5.11 < 5.15.75.15.7
linuxlinux_kernel>= 5.4 < 5.4.1645.4.164
linuxlinux_kernel>= 5.5 < 5.10.845.10.84

CVSS provenance

nvdv3.15.5MEDIUMCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
osv5.5MEDIUM
vendor_debian5.5MEDIUM
vendor_redhat5.5MEDIUM
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