CVE-2024-47736 erofs: handle overlapped pclusters out of crafted images properly
A crafted EROFS filesystem image can cause a kernel deadlock and task hang, 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-2024-47736?
CVE-2024-47736 is a medium-severity denial of service vulnerability in Linux kernel, published on 21 Oct 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:
erofs: handle overlapped pclusters out of crafted images properly
syzbot reported a task hang issue due to a deadlock case where it is waiting for the folio lock of a cached folio that will be used for cache I/Os.
After looking into the crafted fuzzed image, I found it's formed with several overlapped big pclusters as below:
Ext: logical offset | length : physical offset | length 0: 0.. 16384 | 16384 : 151552.. 167936 | 16384 1: 16384.. 32768 | 16384 : 155648.. 172032 | 16384 2: 32768.. 49152 | 16384 : 537223168.. 537239552 | 16384 ...
Here, extent 0/1 are physically overlapped although it's entirely _impossible_ for normal filesystem images generated by mkfs.
First, managed folios containing compressed data will be marked as up-to-date and then unlocked immediately (unlike in-place folios) when compressed I/Os are complete. If physical blocks are not submitted in the incremental order, there should be separate BIOs to avoid dependency issues. However, the current code mis-arranges z_erofs_fill_bio_vec() and BIO submission which causes unexpected BIO waits.
Second, managed folios will be connected to their own pclusters for efficient inter-queries. However, this is somewhat hard to implement easily if overlapped big pclusters exist. Again, these only appear in fuzzed images so let's simply fall back to temporary short-lived pages for correctness.
Additionally, it justifies that referenced managed folios cannot be truncated for now and reverts part of commit 2080ca1ed3e4 ("erofs: tidy up `struct z_erofs_bvec`") for simplicity although it shouldn't be any difference.
Weakness: CWE-667
Which versions are affected by CVE-2024-47736?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2024-47736?
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-2024-47736 being exploited?
There is no known exploitation of CVE-2024-47736 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-50754, AZL-50883, BELL-CVE-2024-47736, DEBIAN-CVE-2024-47736, GHSA-fh88-v2mj-cp79, ROOT-OS-DEBIAN-12-CVE-2024-47736 and 2 more.