CVE-2021-47214: linux kernel — Fix

Description

In the Linux kernel, the following vulnerability has been resolved: hugetlb, userfaultfd: fix reservation restore on userfaultfd error Currently in the is_continue case in hugetlb_mcopy_atomic_pte(), if we bail out using "goto out_release_unlock;" in the cases where idx >= size, or !huge_pte_none(), the code will detect that new_pagecache_page == false, and so call restore_reserve_on_error(). In this case I see restore_reserve_on_error() delete the reservation, and the following call to remove_inode_hugepages() will increment h->resv_hugepages causing a 100% reproducible leak. We should treat the is_continue case similar to adding a page into the pagecache and set new_pagecache_page to true, to indicate that there is no reservation to restore on the error path, and we need not call restore_reserve_on_error(). Rename new_pagecache_page to page_in_pagecache to make that clear.

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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-401 CWE-401

Affected Products

Vendor	Product	Versions
linux	linux_kernel	5.14 — 5.15.5
linux	linux_kernel	All
linux	linux_kernel	All

References

Advisories & Patches

https://git.kernel.org/stable/c/b5069d44e2fbc4a9093d005b3ef0949add3dd27e https://git.kernel.org/stable/c/cc30042df6fcc82ea18acf0dace831503e60a0b7 https://git.kernel.org/stable/c/b5069d44e2fbc4a9093d005b3ef0949add3dd27e https://git.kernel.org/stable/c/cc30042df6fcc82ea18acf0dace831503e60a0b7

Frequently Asked Questions

What is CVE-2021-47214? +

In the Linux kernel, the following vulnerability has been resolved: hugetlb, userfaultfd: fix reservation restore on userfaultfd error Currently in the is_continue case in hugetlb_mcopy_atomic_pte(), if we bail out using "goto out_release_unlock;" in the cases where idx >= size, or !huge_pte_none(), the code will detect that new_pagecache_page == false, and so call restore_reserve_on_error(). In this case I see restore_reserve_on_error() delete the reservation, and the following call to remove_inode_hugepages() will increment h->resv_hugepages causing a 100% reproducible leak. We should treat the is_continue case similar to adding a page into the pagecache and set new_pagecache_page to true, to indicate that there is no reservation to restore on the error path, and we need not call restore_reserve_on_error(). Rename new_pagecache_page to page_in_pagecache to make that clear. It has a CVSS v3.1 base score of 5.5 (MEDIUM).

How severe is CVE-2021-47214? +

CVE-2021-47214 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-2021-47214? +

CVE-2021-47214 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-2021-47214? +

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-2021-47214