Subject: CVE-2024-49924: fbdev: pxafb: Fix possible use after free in pxafb_task()

From: Greg Kroah-Hartman <[email-masked]>

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

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

fbdev: pxafb: Fix possible use after free in pxafb_task()

In the pxafb_probe function, it calls the pxafb_init_fbinfo function,
after which &fbi->task is associated with pxafb_task. Moreover,
within this pxafb_init_fbinfo function, the pxafb_blank function
within the &pxafb_ops struct is capable of scheduling work.

If we remove the module which will call pxafb_remove to make cleanup,
it will call unregister_framebuffer function which can call
do_unregister_framebuffer to free fbi->fb through
put_fb_info(fb_info), while the work mentioned above will be used.
The sequence of operations that may lead to a UAF bug is as follows:

CPU0                                                CPU1

                                   | pxafb_task
pxafb_remove                       |
unregister_framebuffer(info)       |
do_unregister_framebuffer(fb_info) |
put_fb_info(fb_info)               |
// free fbi->fb                    | set_ctrlr_state(fbi, state)
                                   | __pxafb_lcd_power(fbi, 0)
                                   | fbi->lcd_power(on, &fbi->fb.var)
                                   | //use fbi->fb

Fix it by ensuring that the work is canceled before proceeding
with the cleanup in pxafb_remove.

Note that only root user can remove the driver at runtime.

The Linux kernel CVE team has assigned CVE-2024-49924 to this issue.

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

	Fixed in 5.10.227 with commit e6897e299f57
	Fixed in 5.15.168 with commit 4cda484e584b
	Fixed in 6.1.113 with commit 3c0d416eb4be
	Fixed in 6.6.55 with commit fdda354f60a5
	Fixed in 6.10.14 with commit aaadc0cb05c9
	Fixed in 6.11.3 with commit a3a855764dba
	Fixed in 6.12-rc1 with commit 4a6921095eb0

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-2024-49924
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/pxafb.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/e6897e299f57b103e999e62010b88e363b3eebae
	https://git.kernel.org/stable/c/4cda484e584be34d55ee17436ebf7ad11922b97a
	https://git.kernel.org/stable/c/3c0d416eb4bef705f699213cee94bf54b6acdacd
	https://git.kernel.org/stable/c/fdda354f60a576d52dcf90351254714681df4370
	https://git.kernel.org/stable/c/aaadc0cb05c999ccd8898a03298b7e5c31509b08
	https://git.kernel.org/stable/c/a3a855764dbacbdb1cc51e15dc588f2d21c93e0e
	https://git.kernel.org/stable/c/4a6921095eb04a900e0000da83d9475eb958e61e