| Summary: |
VUL-0: CVE-2021-47546: kernel: ipv6: fix memory leak in fib6_rule_suppress |
| Product: |
[Novell Products] SUSE Security Incidents
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Reporter: |
SMASH SMASH <smash_bz> |
| Component: |
Incidents | Assignee: |
Davide Benini <davide.benini> |
| Status: |
NEW
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QA Contact: |
Security Team bot <security-team> |
| Severity: |
Normal
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| Priority: |
P3 - Medium
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CC: |
andrea.mattiazzo, jlee
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| Version: |
unspecified | |
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| Target Milestone: |
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| Hardware: |
Other | |
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| OS: |
Other | |
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| URL: |
https://smash.suse.de/issue/407706/
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| Whiteboard: |
CVSSv3.1:SUSE:CVE-2021-47546:2.3:(AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L) |
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Found By:
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Security Response Team
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Services Priority:
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Business Priority:
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Blocker:
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Marketing QA Status:
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IT Deployment:
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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 References: http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-47546 https://www.cve.org/CVERecord?id=CVE-2021-47546 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 https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2021/CVE-2021-47546.mbox https://bugzilla.redhat.com/show_bug.cgi?id=2283403