CVE-2026-53402fbdev: fbcon: fix out-of-bounds read in err_out of fbcon_do_set_font()

Official description

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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/cb016bcb40c81e7b19c4ae6143babb366dae8e20
• https://git.kernel.org/stable/c/ac562193c36696513ae196171892e9338475c4bc
• https://git.kernel.org/stable/c/3618a4c5b2591cfa83efe74f5b18c2d02b35c3f5
• https://git.kernel.org/stable/c/a7a526fbc847f07ad3a503c7382189be5ab68574
• https://git.kernel.org/stable/c/b5bb2c696e140c399cb874def2feedf61dee27d6
• https://git.kernel.org/stable/c/076b1aa65f77a49bce5a48a4a55a397cfcafa2b8
• https://git.kernel.org/stable/c/39815715cbcfabb16fc8c5f4a23deeda20f5df62
• https://git.kernel.org/stable/c/8fdc8c2057eea08d40ce2c8eed41ff9e451c65c2