CVE-2024-49873 mm/filemap: fix filemap_get_folios_contig THP panic
A local attacker can trigger a kernel panic via memfd_pin_folios with unaligned THP offsets, causing 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-2024-49873?
CVE-2024-49873 is a medium-severity 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:
mm/filemap: fix filemap_get_folios_contig THP panic
Patch series "memfd-pin huge page fixes".
Fix multiple bugs that occur when using memfd_pin_folios with hugetlb pages and THP. The hugetlb bugs only bite when the page is not yet faulted in when memfd_pin_folios is called. The THP bug bites when the starting offset passed to memfd_pin_folios is not huge page aligned. See the commit messages for details.
This patch (of 5):
memfd_pin_folios on memory backed by THP panics if the requested start offset is not huge page aligned:
BUG: kernel NULL pointer dereference, address: 0000000000000036 RIP: 0010:filemap_get_folios_contig+0xdf/0x290 RSP: 0018:ffffc9002092fbe8 EFLAGS: 00010202 RAX: 0000000000000002 RBX: 0000000000000002 RCX: 0000000000000002
The fault occurs here, because xas_load returns a folio with value 2:
filemap_get_folios_contig() for (folio = xas_load(&xas); folio && xas.xa_index <= end; folio = xas_next(&xas)) { ... if (!folio_try_get(folio)) <-- BOOM
"2" is an xarray sibling entry. We get it because memfd_pin_folios does not round the indices passed to filemap_get_folios_contig to huge page boundaries for THP, so we load from the middle of a huge page range see a sibling. (It does round for hugetlbfs, at the is_file_hugepages test).
To fix, if the folio is a sibling, then return the next index as the starting point for the next call to filemap_get_folios_contig.
Weakness: CWE-476
Which versions are affected by CVE-2024-49873?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2024-49873?
Apply the vendor's patch.
Is CVE-2024-49873 being exploited?
There is no known exploitation of CVE-2024-49873 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2024-49873, DEBIAN-CVE-2024-49873, GHSA-j2cc-c4fg-77cq, UBUNTU-CVE-2024-49873.