CVE-2021-47227: linux kernel — Fix

Description

In the Linux kernel, the following vulnerability has been resolved: x86/fpu: Prevent state corruption in __fpu__restore_sig() The non-compacted slowpath uses __copy_from_user() and copies the entire user buffer into the kernel buffer, verbatim. This means that the kernel buffer may now contain entirely invalid state on which XRSTOR will #GP. validate_user_xstate_header() can detect some of that corruption, but that leaves the onus on callers to clear the buffer. Prior to XSAVES support, it was possible just to reinitialize the buffer, completely, but with supervisor states that is not longer possible as the buffer clearing code split got it backwards. Fixing that is possible but not corrupting the state in the first place is more robust. Avoid corruption of the kernel XSAVE buffer by using copy_user_to_xstate() which validates the XSAVE header contents before copying the actual states to the kernel. copy_user_to_xstate() was previously only called for compacted-format kernel buffers, but it works for both compacted and non-compacted forms. Using it for the non-compacted form is slower because of multiple __copy_from_user() operations, but that cost is less important than robust code in an already slow path. [ Changelog polished by Dave Hansen ]

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CVSS v3.1 Score

5.5

MEDIUM

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Weakness Type (CWE)

CWE-754 CWE-754

Affected Products

Vendor	Product	Versions
linux	linux_kernel	5.8 — 5.10.46
linux	linux_kernel	5.11 — 5.12.13
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All

References

Advisories & Patches

https://git.kernel.org/stable/c/076f732b16a5bf842686e1b43ab6021a2d98233e https://git.kernel.org/stable/c/484cea4f362e1eeb5c869abbfb5f90eae6421b38 https://git.kernel.org/stable/c/ec25ea1f3f05d6f8ee51d1277efea986eafd4f2a https://git.kernel.org/stable/c/076f732b16a5bf842686e1b43ab6021a2d98233e https://git.kernel.org/stable/c/484cea4f362e1eeb5c869abbfb5f90eae6421b38 https://git.kernel.org/stable/c/ec25ea1f3f05d6f8ee51d1277efea986eafd4f2a

Frequently Asked Questions

What is CVE-2021-47227? +

In the Linux kernel, the following vulnerability has been resolved: x86/fpu: Prevent state corruption in __fpu__restore_sig() The non-compacted slowpath uses __copy_from_user() and copies the entire user buffer into the kernel buffer, verbatim. This means that the kernel buffer may now contain entirely invalid state on which XRSTOR will #GP. validate_user_xstate_header() can detect some of that corruption, but that leaves the onus on callers to clear the buffer. Prior to XSAVES support, it was possible just to reinitialize the buffer, completely, but with supervisor states that is not longer possible as the buffer clearing code split got it backwards. Fixing that is possible but not corrupting the state in the first place is more robust. Avoid corruption of the kernel XSAVE buffer by using copy_user_to_xstate() which validates the XSAVE header contents before copying the actual states to the kernel. copy_user_to_xstate() was previously only called for compacted-format kernel buffers, but it works for both compacted and non-compacted forms. Using it for the non-compacted form is slower because of multiple __copy_from_user() operations, but that cost is less important than robust code in an already slow path. [ Changelog polished by Dave Hansen ] It has a CVSS v3.1 base score of 5.5 (MEDIUM).

How severe is CVE-2021-47227? +

CVE-2021-47227 has a CVSS v3.1 score of 5.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.

What products are affected by CVE-2021-47227? +

CVE-2021-47227 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2021-47227? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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CVE-2021-47227