CVE-2024-49873: mm/filemap: fix filemap_get_folios_contig THP panic

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-10-21 · updated 2026-06-17
Weakness: CWE-476

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.

Affected products

Linux kernel: from 6.11 before 6.11.3 — fixed in 6.11.3

How to fix

Upgrade to a fixed version: Linux kernel 6.11.3. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2024-49873 or the next vulnerability affects your stack