CVE-2024-49873 Information

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.

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Reference

https://git.kernel.org/stable/c/570dd14bfecf281fa467c80f8ec92b26370ee36a https://git.kernel.org/stable/c/c225c4f6056b46a8a5bf2ed35abf17a2d6887691

Attack Complexity

LOW

Privileges Required

LOW

User Interaction Required

LOW

Scope

NONE

Confidentiality Impact

UNCHANGED

Integrity Impact

NONE

Availability Impact

NONE

Base Score

HIGH

Base Severity

5.5