CVE-2021-47383: tty: Fix out-of-bound vmalloc access in imageblit

Severity: high (CVSS 7.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-05-21 · updated 2026-08-04
Weakness: CWE-125

Description

In the Linux kernel, the following vulnerability has been resolved: tty: Fix out-of-bound vmalloc access in imageblit This issue happens when a userspace program does an ioctl FBIOPUT_VSCREENINFO passing the fb_var_screeninfo struct containing only the fields xres, yres, and bits_per_pixel with values. If this struct is the same as the previous ioctl, the vc_resize() detects it and doesn't call the resize_screen(), leaving the fb_var_screeninfo incomplete. And this leads to the updatescrollmode() calculates a wrong value to fbcon_display->vrows, which makes the real_y() return a wrong value of y, and that value, eventually, causes the imageblit to access an out-of-bound address value. To solve this issue I made the resize_screen() be called even if the screen does not need any resizing, so it will "fix and fill" the fb_var_screeninfo independently.

Affected products

Linux kernel: before 4.4.286; from 4.5 before 4.9.285; from 4.10 before 4.14.249; from 4.15 before 4.19.209; from 4.20 before 5.4.151; from 5.5 before 5.10.71 — fixed in 4.14.249, 4.19.209, 4.4.286, 4.9.285, 5.10.71, 5.14.10

How to fix

Upgrade to a fixed version: Linux kernel 4.14.249, 4.19.209, 4.4.286, 4.9.285. Check the vendor advisory for mitigations.

References

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