# CVE-2024-49873: linux: In the Linux kernel, the following vulnerability has been resolved:  mm/filemap: fix filemap_get_folios_contig THP pa...

CVE-2024-49873 is fixed in linux on 1 platform, first by DEBIAN-CVE-2024-49873, released October 21, 2024. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2024-49873
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0020
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 21, 2024

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.11.4-1 | [DEBIAN-CVE-2024-49873](https://patchblox.com/security/data/fix/linux/debian-cve-2024-49873.md) | Oct 21, 2024 |
| Linux | linux Debian 14 | 6.11.4-1 | [DEBIAN-CVE-2024-49873](https://patchblox.com/security/data/fix/linux/debian-cve-2024-49873.md) | Oct 21, 2024 |

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