CVE-2026-89718: zram: fix out-of-bounds access in writeback_store()

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

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

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

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

zram: fix out-of-bounds access in writeback_store()

Patch series "zram: fix stale scan bounds after reinitialization".

Both writeback_store() and read_block_state() derive their table scan
bounds from zram->disksize before acquiring dev_lock.  If the device is
reset and reinitialized with a smaller disksize between that read and lock
acquisition, the bound can describe the old table while the scan operates
on the new one.  This can lead to out-of-bounds slot accesses.

Move both bound calculations under dev_lock so each bound remains
consistent with the table throughout its scan.  Keep the fixes separate
because the affected interfaces originate from different commits and can
be backported independently.


This patch (of 2):

writeback_store() calculates the table scan bounds before taking dev_lock.
A reset followed by reconfiguration with a smaller disksize can therefore
replace zram->table while writeback_store() is waiting for the lock.  Once
it acquires the lock, it sees an initialized device but scans the new
table using the old upper bound, resulting in an out-of-bounds access.

Calculate the number of pages while holding dev_lock so the scan bound
matches the table protected by the lock.

The Linux kernel CVE team has assigned CVE-2026-89718 to this issue.


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

	Issue introduced in 5.0 with commit a939888ec38bf1f33e4a903056677e92a4844244 and fixed in 7.2.4 with commit 07a82a66f8c1894d92e51d97542c32ebf2c51b09
	Issue introduced in 5.0 with commit a939888ec38bf1f33e4a903056677e92a4844244 and fixed in 7.3-rc1 with commit 894913e2d35c46ff19a77530907771ae57862b96

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-2026-89718
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


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/07a82a66f8c1894d92e51d97542c32ebf2c51b09
	https://git.kernel.org/stable/c/894913e2d35c46ff19a77530907771ae57862b96