CVE-2021-47365: afs: Fix page leak

Vulnerability summary

CVE-2021-47365 is a medium (CVSS 5.5) Incomplete Cleanup vulnerability in linux. EPSS estimates a 0.21% chance of exploitation in the next 30 days, higher than 10.9% of scored vulnerabilities.

Timeline

1. 21-05-2024
   PublishedVulnerability first disclosed.
2. 11-05-2026
   Last modifiedVulnerability information updated.

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".

• CWE-459Incomplete CleanupThe product does not properly "clean up" and remove temporary or supporting resources after they have been used.