Linux Kernel up to 5.15.4 userfaultfd hugetlb_mcopy_atomic_pte memory leak

Summaryinfo

A vulnerability, which was classified as problematic, has been found in Linux Kernel up to 5.15.4. Affected is the function hugetlb_mcopy_atomic_pte of the component userfaultfd. The manipulation leads to an unknown weakness. This vulnerability is listed as CVE-2021-47214. There is no available exploit. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in Linux Kernel up to 5.15.4 and classified as problematic. This issue affects the function hugetlb_mcopy_atomic_pte of the component userfaultfd. Using CWE to declare the problem leads to CWE-401. The product does not sufficiently track and release allocated memory after it has been used, which slowly consumes remaining memory. The impact remains unknown. The summary by CVE is:

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 is possible to read the advisory at git.kernel.org. The identification of this vulnerability is CVE-2021-47214. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 5.15.5 or 5.16 eliminates this vulnerability. Applying the patch b5069d44e2fb/cc30042df6fc is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 5.15.0
• 5.15.1
• 5.15.2
• 5.15.3
• 5.15.4

License

• open-source

Website

• Vendor: https://www.kernel.org/

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