linux-cve-announce - CVE-2025-21976: fbdev: hyperv_fb: Allow graceful removal of framebuffer

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Message-ID: <2025040147-CVE-2025-21976-340d@gregkh>
Date: Tue,  1 Apr 2025 16:46:01 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-21976: fbdev: hyperv_fb: Allow graceful removal of framebuffer

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

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

fbdev: hyperv_fb: Allow graceful removal of framebuffer

When a Hyper-V framebuffer device is unbind, hyperv_fb driver tries to
release the framebuffer forcefully. If this framebuffer is in use it
produce the following WARN and hence this framebuffer is never released.

[   44.111220] WARNING: CPU: 35 PID: 1882 at drivers/video/fbdev/core/fb_info.c:70 framebuffer_release+0x2c/0x40
< snip >
[   44.111289] Call Trace:
[   44.111290]  <TASK>
[   44.111291]  ? show_regs+0x6c/0x80
[   44.111295]  ? __warn+0x8d/0x150
[   44.111298]  ? framebuffer_release+0x2c/0x40
[   44.111300]  ? report_bug+0x182/0x1b0
[   44.111303]  ? handle_bug+0x6e/0xb0
[   44.111306]  ? exc_invalid_op+0x18/0x80
[   44.111308]  ? asm_exc_invalid_op+0x1b/0x20
[   44.111311]  ? framebuffer_release+0x2c/0x40
[   44.111313]  ? hvfb_remove+0x86/0xa0 [hyperv_fb]
[   44.111315]  vmbus_remove+0x24/0x40 [hv_vmbus]
[   44.111323]  device_remove+0x40/0x80
[   44.111325]  device_release_driver_internal+0x20b/0x270
[   44.111327]  ? bus_find_device+0xb3/0xf0

Fix this by moving the release of framebuffer and assosiated memory
to fb_ops.fb_destroy function, so that framebuffer framework handles
it gracefully.

While we fix this, also replace manual registrations/unregistration of
framebuffer with devm_register_framebuffer.

The Linux kernel CVE team has assigned CVE-2025-21976 to this issue.


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

	Issue introduced in 3.10 with commit 68a2d20b79b105f02dcbc52c211d7e62f98996b7 and fixed in 6.12.20 with commit 4545e2aa121aea304d33903099c03e29ed4fe50a
	Issue introduced in 3.10 with commit 68a2d20b79b105f02dcbc52c211d7e62f98996b7 and fixed in 6.13.8 with commit a7b583dc99c6cf4a96877017be1d08247e1ef2c7
	Issue introduced in 3.10 with commit 68a2d20b79b105f02dcbc52c211d7e62f98996b7 and fixed in 6.14 with commit ea2f45ab0e53b255f72c85ccd99e2b394fc5fceb

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-2025-21976
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/video/fbdev/hyperv_fb.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/4545e2aa121aea304d33903099c03e29ed4fe50a
	https://git.kernel.org/stable/c/a7b583dc99c6cf4a96877017be1d08247e1ef2c7
	https://git.kernel.org/stable/c/ea2f45ab0e53b255f72c85ccd99e2b394fc5fceb