CVE-2021-47109: neighbour: allow NUD_NOARP entries to be forced GCed

CVE-2021-47109: neighbour: allow NUD_NOARP entries to be forced GCed

[Greg Kroah-Hartman]

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

neighbour: allow NUD_NOARP entries to be forced GCed

IFF_POINTOPOINT interfaces use NUD_NOARP entries for IPv6. It's possible to
fill up the neighbour table with enough entries that it will overflow for
valid connections after that.

This behaviour is more prevalent after commit 58956317c8de ("neighbor:
Improve garbage collection") is applied, as it prevents removal from
entries that are not NUD_FAILED, unless they are more than 5s old.

The Linux kernel CVE team has assigned CVE-2021-47109 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.0 with commit 58956317c8de and fixed in 5.4.125 with commit d99029e6aab6
	Issue introduced in 5.0 with commit 58956317c8de and fixed in 5.10.43 with commit d17d47da59f7
	Issue introduced in 5.0 with commit 58956317c8de and fixed in 5.12.10 with commit ddf088d7aaaa
	Issue introduced in 5.0 with commit 58956317c8de and fixed in 5.13 with commit 7a6b1ab7475f

Please see https://www.kernel.org or a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2021-47109
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/core/neighbour.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/d99029e6aab62aef0a0251588b2867e77e83b137
	https://git.kernel.org/stable/c/d17d47da59f726dc4c87caebda3a50333d7e2fd3
	https://git.kernel.org/stable/c/ddf088d7aaaaacfc836104f2e632b29b1d383cfc
	https://git.kernel.org/stable/c/7a6b1ab7475fd6478eeaf5c9d1163e7a18125c8f