CVE-2024-57952 Revert "libfs: fix infinite directory reads for offset dir"
A logic error in the Linux kernel directory offset allocator causes directory entries to become permanently invisible on 32-bit systems after counter wrap.
- 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-2024-57952?
CVE-2024-57952 is a high-severity denial of service vulnerability in Linux kernel, published on 12 Feb 2025. 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:
Revert "libfs: fix infinite directory reads for offset dir"
The current directory offset allocator (based on mtree_alloc_cyclic) stores the next offset value to return in octx->next_offset. This mechanism typically returns values that increase monotonically over time. Eventually, though, the newly allocated offset value wraps back to a low number (say, 2) which is smaller than other already- allocated offset values.
Yu Kuai <[email protected]> reports that, after commit 64a7ce76fb90 ("libfs: fix infinite directory reads for offset dir"), if a directory's offset allocator wraps, existing entries are no longer visible via readdir/getdents because offset_readdir() stops listing entries once an entry's offset is larger than octx->next_offset. These entries vanish persistently -- they can be looked up, but will never again appear in readdir(3) output.
The reason for this is that the commit treats directory offsets as monotonically increasing integer values rather than opaque cookies, and introduces this comparison:
if (dentry2offset(dentry) >= last_index) {
On 64-bit platforms, the directory offset value upper bound is 2^63 - 1. Directory offsets will monotonically increase for millions of years without wrapping.
On 32-bit platforms, however, LONG_MAX is 2^31 - 1. The allocator can wrap after only a few weeks (at worst).
Revert commit 64a7ce76fb90 ("libfs: fix infinite directory reads for offset dir") to prepare for a fix that can work properly on 32-bit systems and might apply to recent LTS kernels where shmem employs the simple_offset mechanism.
Which versions are affected by CVE-2024-57952?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2024-57952?
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-2024-57952 being exploited?
There is no known exploitation of CVE-2024-57952 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2024-57952, DEBIAN-CVE-2024-57952, GHSA-qxjr-36pm-q2q2, ROOT-OS-DEBIAN-11-CVE-2024-57952, ROOT-OS-DEBIAN-12-CVE-2024-57952, ROOT-OS-UBUNTU-2204-CVE-2024-57952 and 1 more.