linux-cve-announce - CVE-2024-57982: xfrm: state: fix out-of-bounds read during lookup

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Message-ID: <2025022635-CVE-2024-57982-c76a@gregkh>
Date: Wed, 26 Feb 2025 18:05:41 -0800
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-57982: xfrm: state: fix out-of-bounds read during lookup

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

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

xfrm: state: fix out-of-bounds read during lookup

lookup and resize can run in parallel.

The xfrm_state_hash_generation seqlock ensures a retry, but the hash
functions can observe a hmask value that is too large for the new hlist
array.

rehash does:
  rcu_assign_pointer(net->xfrm.state_bydst, ndst) [..]
  net->xfrm.state_hmask = nhashmask;

While state lookup does:
  h = xfrm_dst_hash(net, daddr, saddr, tmpl->reqid, encap_family);
  hlist_for_each_entry_rcu(x, net->xfrm.state_bydst + h, bydst) {

This is only safe in case the update to state_bydst is larger than
net->xfrm.xfrm_state_hmask (or if the lookup function gets
serialized via state spinlock again).

Fix this by prefetching state_hmask and the associated pointers.
The xfrm_state_hash_generation seqlock retry will ensure that the pointer
and the hmask will be consistent.

The existing helpers, like xfrm_dst_hash(), are now unsafe for RCU side,
add lockdep assertions to document that they are only safe for insert
side.

xfrm_state_lookup_byaddr() uses the spinlock rather than RCU.
AFAICS this is an oversight from back when state lookup was converted to
RCU, this lock should be replaced with RCU in a future patch.

The Linux kernel CVE team has assigned CVE-2024-57982 to this issue.

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

	Issue introduced in 4.9 with commit c2f672fc94642bae96821a393f342edcfa9794a6 and fixed in 6.12.13 with commit a16871c7832ea6435abb6e0b58289ae7dcb7e4fc
	Issue introduced in 4.9 with commit c2f672fc94642bae96821a393f342edcfa9794a6 and fixed in 6.13.2 with commit dd4c2a174994238d55ab54da2545543d36f4e0d0
	Issue introduced in 4.9 with commit c2f672fc94642bae96821a393f342edcfa9794a6 and fixed in 6.14-rc1 with commit e952837f3ddb0ff726d5b582aa1aad9aa38d024d

Please see https://www.kernel.org for 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-2024-57982
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/xfrm/xfrm_state.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/a16871c7832ea6435abb6e0b58289ae7dcb7e4fc
	https://git.kernel.org/stable/c/dd4c2a174994238d55ab54da2545543d36f4e0d0
	https://git.kernel.org/stable/c/e952837f3ddb0ff726d5b582aa1aad9aa38d024d