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CVE-2021-47546
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CVE-2021-47546
MITRE ATT&CK
Collection
Command and Control
Credential Access
Defense Evasion
Discovery
Execution
Exfiltration
Impact
Initial Access
Lateral Movement
Persistence
Privilege Escalation
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Description
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.
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- linux
Products
- linux kernel
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