CVE-2021-47365: linux kernel — Fix

Description

In the Linux kernel, the following vulnerability has been resolved: afs: Fix page leak There's a loop in afs_extend_writeback() that adds extra pages to a write we want to make to improve the efficiency of the writeback by making it larger. This loop stops, however, if we hit a page we can't write back from immediately, but it doesn't get rid of the page ref we speculatively acquired. This was caused by the removal of the cleanup loop when the code switched from using find_get_pages_contig() to xarray scanning as the latter only gets a single page at a time, not a batch. Fix this by putting the page on a ref on an early break from the loop. Unfortunately, we can't just add that page to the pagevec we're employing as we'll go through that and add those pages to the RPC call. This was found by the generic/074 test. It leaks ~4GiB of RAM each time it is run - which can be observed with "top".

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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-459 CWE-459

Affected Products

Vendor	Product	Versions
linux	linux_kernel	5.13 — 5.14.9
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All

References

Advisories & Patches

https://git.kernel.org/stable/c/581b2027af0018944ba301d68e7af45c6d1128b5 https://git.kernel.org/stable/c/d130b5fdd42254d92948d06347940276140c927e https://git.kernel.org/stable/c/581b2027af0018944ba301d68e7af45c6d1128b5 https://git.kernel.org/stable/c/d130b5fdd42254d92948d06347940276140c927e

Frequently Asked Questions

What is CVE-2021-47365? +

In the Linux kernel, the following vulnerability has been resolved: afs: Fix page leak There's a loop in afs_extend_writeback() that adds extra pages to a write we want to make to improve the efficiency of the writeback by making it larger. This loop stops, however, if we hit a page we can't write back from immediately, but it doesn't get rid of the page ref we speculatively acquired. This was caused by the removal of the cleanup loop when the code switched from using find_get_pages_contig() to xarray scanning as the latter only gets a single page at a time, not a batch. Fix this by putting the page on a ref on an early break from the loop. Unfortunately, we can't just add that page to the pagevec we're employing as we'll go through that and add those pages to the RPC call. This was found by the generic/074 test. It leaks ~4GiB of RAM each time it is run - which can be observed with "top". It has a CVSS v3.1 base score of 5.5 (MEDIUM).

How severe is CVE-2021-47365? +

CVE-2021-47365 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-2021-47365? +

CVE-2021-47365 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-2021-47365? +

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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