linux-cve-announce - CVE-2025-38620: zloop: fix KASAN use-after-free of tag set

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Message-ID: <2025082229-CVE-2025-38620-1dc9@gregkh>
Date: Fri, 22 Aug 2025 18:00:29 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38620: zloop: fix KASAN use-after-free of tag set

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

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

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

zloop: fix KASAN use-after-free of tag set

When a zoned loop device, or zloop device, is removed, KASAN enabled
kernel reports "BUG KASAN use-after-free" in blk_mq_free_tag_set(). The
BUG happens because zloop_ctl_remove() calls put_disk(), which invokes
zloop_free_disk(). The zloop_free_disk() frees the memory allocated for
the zlo pointer. However, after the memory is freed, zloop_ctl_remove()
calls blk_mq_free_tag_set(&zlo->tag_set), which accesses the freed zlo.
Hence the KASAN use-after-free.

 zloop_ctl_remove()
  put_disk(zlo->disk)
   put_device()
    kobject_put()
     ...
      zloop_free_disk()
        kvfree(zlo)
  blk_mq_free_tag_set(&zlo->tag_set)

To avoid the BUG, move the call to blk_mq_free_tag_set(&zlo->tag_set)
from zloop_ctl_remove() into zloop_free_disk(). This ensures that
the tag_set is freed before the call to kvfree(zlo).

The Linux kernel CVE team has assigned CVE-2025-38620 to this issue.

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

	Issue introduced in 6.16 with commit eb0570c7df23c2f32fe899fcdaf8fca9a5ecd51e and fixed in 6.16.1 with commit c7c87046b41a9ef28ee7ac476c369da5b5228bc5
	Issue introduced in 6.16 with commit eb0570c7df23c2f32fe899fcdaf8fca9a5ecd51e and fixed in 6.17-rc1 with commit 765761851d89c772f482494d452e266795460278

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-2025-38620
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/zloop.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/c7c87046b41a9ef28ee7ac476c369da5b5228bc5
	https://git.kernel.org/stable/c/765761851d89c772f482494d452e266795460278