CVE-2021-47365 afs: Fix page leak
A page reference leak in the Linux kernel AFS filesystem can cause significant memory exhaustion, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2021-47365?
CVE-2021-47365 is a medium-severity denial of service vulnerability in Linux kernel, published on 21 May 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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".
Weakness: CWE-459
Which versions are affected by CVE-2021-47365?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2021-47365?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2021-47365 being exploited?
There is no known exploitation of CVE-2021-47365 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as DEBIAN-CVE-2021-47365, GHSA-95jq-x6q9-c9cq, UBUNTU-CVE-2021-47365.