CVE-2026-81013: platform/x86: hp-bioscfg: fix heap OOB read on empty password write

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

platform/x86: hp-bioscfg: fix heap OOB read on empty password write

validate_password_input() computes length = strlen(buf) and then
checks buf[length - 1] to strip a trailing newline, without checking
that length is nonzero first. Writing an empty string (a bare '\n')
to current_password or new_password gives length == 0, and
buf[length - 1] reads buf[-1], one byte before the heap allocation
holding the copied input.

KASAN confirms this directly:

  BUG: KASAN: slab-out-of-bounds in store_password_instance.constprop.0+0x223/0x2a0 [hp_bioscfg]
  Read of size 1 at addr ffff88811bd8da9f by task sh/13740
  ...
  store_password_instance.constprop.0+0x223/0x2a0 [hp_bioscfg]
  current_password_store+0x14/0x20 [hp_bioscfg]
  ...
  The buggy address is located 23 bytes to the right of
  allocated 8-byte region [ffff88811bd8da80, ffff88811bd8da88)

Reproduced identically via new_password_store. Execution continues
past the bad read (the garbage byte only affects whether "length" is
decremented by one), so the write completes and returns success; this
is a pure information read past the buffer, not a crash, but it is
still an out-of-bounds access KASAN correctly flags.

Fix by only checking buf[length - 1] when length is nonzero.

The Linux kernel CVE team has assigned CVE-2026-81013 to this issue.


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

	Issue introduced in 6.6 with commit 8646a3b5ee3a5b384a22a721f37c24274d974045 and fixed in 6.12.109 with commit cecb8154bd5fa6c8ddbd1a4e8216bbc0f0eb9828
	Issue introduced in 6.6 with commit 8646a3b5ee3a5b384a22a721f37c24274d974045 and fixed in 6.18.50 with commit 0f9aad08424882dd5714b53d29ae044060890752
	Issue introduced in 6.6 with commit 8646a3b5ee3a5b384a22a721f37c24274d974045 and fixed in 7.2.4 with commit b699e5c1f63a9e79946c35598c8a6f7af2c356b8
	Issue introduced in 6.6 with commit 8646a3b5ee3a5b384a22a721f37c24274d974045 and fixed in 7.3-rc1 with commit 2b2ec354f905c14e3270e8ec3ab50f7d8ad73bab

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-2026-81013
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:
	drivers/platform/x86/hp/hp-bioscfg/passwdobj-attributes.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/cecb8154bd5fa6c8ddbd1a4e8216bbc0f0eb9828
	https://git.kernel.org/stable/c/0f9aad08424882dd5714b53d29ae044060890752
	https://git.kernel.org/stable/c/b699e5c1f63a9e79946c35598c8a6f7af2c356b8
	https://git.kernel.org/stable/c/2b2ec354f905c14e3270e8ec3ab50f7d8ad73bab