In the Linux kernel, the following vulnerability has been resolved: fbdev: fbcon: fix out-of-bounds read in err_out of fbcon_do_set_font() When fbcon_do_set_font() fails (e.g., due to a memory allocation failure inside vc_resize() unde…

Overview

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

fbdev: fbcon: fix out-of-bounds read in err_out of fbcon_do_set_font()

When fbcon_do_set_font() fails (e.g., due to a memory allocation failure inside vc_resize() under heavy memory pressure), it jumps to the err_out label to roll back the console state. However, the current rollback logic forgets to restore the hi_font state, leading to a severe state machine corruption.

Earlier in the function, set_vc_hi_font() might be called to change vc->vc_hi_font_mask and mutate the screen buffer. If vc_resize() subsequently fails, the err_out path restores vc_font.charcount but entirely skips rolling back the vc_hi_font_mask and the screen buffer.

This mismatch leaves the terminal in a desynchronized state. Because vc_hi_font_mask remains set, the VT subsystem will still accept character indices greater than 255 from userspace and write them to the screen buffer. Subsequent rendering calls (e.g., fbcon_putcs()) will then use these inflated indices to access the reverted, 256-character font array, leading to a deterministic out-of-bounds read and potential kernel memory disclosure.

Fix this by adding the missing rollback logic for the hi_font mask and screen buffer in the error path.

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.