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

What is CVE-2024-49924?

CVE-2024-49924 is a high-severity use after free vulnerability in Debian Debian Linux, published on 21 Oct 2024. It can only be exploited from the same machine or local network, with no action from the victim.

Official 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.

Weakness: CWE-416

Which versions are affected by CVE-2024-49924?

It affects 2 products.

Products include Debian Debian Linux, Linux kernel.

How do I fix CVE-2024-49924?

Apply the vendor's patch.

Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.

Is CVE-2024-49924 being exploited?

There is no known exploitation of CVE-2024-49924 in the wild and no public exploit code.

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All Debian Debian Linux vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as AZL-51523, BELL-CVE-2024-49924, DEBIAN-CVE-2024-49924, GHSA-3rvw-7pxp-g8xm, ROOT-OS-DEBIAN-11-CVE-2024-49924, UBUNTU-CVE-2024-49924.