🛡️ CVE-2025-38685 — debian-linux

fbdev: Fix vmalloc out-of-bounds write in fast_imageblit

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

fbdev: Fix vmalloc out-of-bounds write in fast_imageblit

This issue triggers when a userspace program does an ioctl

FBIOPUT_CON2FBMAP by passing console number and frame buffer number.

Ideally this maps console to frame buffer and updates the screen if

console is visible.

As part of mapping it has to do resize of console according to frame

buffer info. if this resize fails and returns from vc_do_resize() and

continues further. At this point console and new frame buffer are mapped

and sets display vars. Despite failure still it continue to proceed

updating the screen at later stages where vc_data is related to previous

frame buffer and frame buffer info and display vars are mapped to new

frame buffer and eventully leading to out-of-bounds write in

fast_imageblit(). This bheviour is excepted only when fg_console is

equal to requested console which is a visible console and updates screen

with invalid struct references in fbcon_putcs().