CVE-2026-90043: zram: fix slot lock bit position on big-endian 64-bit

CVE-2026-90043: zram: fix slot lock bit position on big-endian 64-bit

[Greg Kroah-Hartman]

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

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

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

zram: fix slot lock bit position on big-endian 64-bit

The slot lock is a bit operation on the whole __lock word, which flags and
ac_time alias as two u32s.  On little-endian the lock bit lands in the
position ZRAM_ENTRY_LOCK reserves in flags, so the aliasing works out.  On
64-bit big-endian it lands in ac_time instead: with
ZRAM_TRACK_ENTRY_ACTIME enabled, storing the access time from
mark_slot_accessed() or slot_free() wipes out the held lock bit, letting
another CPU take the same slot lock; an access time value with that bit
set makes the slot look locked forever.

Shift the lock bit into the flags half of the word on big-endian 64-bit.

The Linux kernel CVE team has assigned CVE-2026-90043 to this issue.


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

	Issue introduced in 7.0 with commit 2e8ff2f51dde73a26b94aed2df4827177bd25e6e and fixed in 7.2.5 with commit 052b6b2d5fe97547bd2cdb73fa894f6cfea68b11
	Issue introduced in 7.0 with commit 2e8ff2f51dde73a26b94aed2df4827177bd25e6e and fixed in 7.3-rc1 with commit a8b5875741d416703e19ad8eeac6fce8a12bd6e4

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-2026-90043
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/block/zram/zram_drv.c
	drivers/block/zram/zram_drv.h


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/052b6b2d5fe97547bd2cdb73fa894f6cfea68b11
	https://git.kernel.org/stable/c/a8b5875741d416703e19ad8eeac6fce8a12bd6e4