CVE-2025-40006 mm/hugetlb: fix folio is still mapped when deleted
A race condition in the Linux kernel's hugetlb subsystem can cause a kernel bug and denial of service when migrating folios during fallocate operations.
- 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-2025-40006?
CVE-2025-40006 is a high-severity vulnerability in Linux, published on 20 Oct 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:
mm/hugetlb: fix folio is still mapped when deleted
Migration may be raced with fallocating hole. remove_inode_single_folio will unmap the folio if the folio is still mapped. However, it's called without folio lock. If the folio is migrated and the mapped pte has been converted to migration entry, folio_mapped() returns false, and won't unmap it. Due to extra refcount held by remove_inode_single_folio, migration fails, restores migration entry to normal pte, and the folio is mapped again. As a result, we triggered BUG in filemap_unaccount_folio.
The log is as follows: BUG: Bad page cache in process hugetlb pfn:156c00 page: refcount:515 mapcount:0 mapping:0000000099fef6e1 index:0x0 pfn:0x156c00 head: order:9 mapcount:1 entire_mapcount:1 nr_pages_mapped:0 pincount:0 aops:hugetlbfs_aops ino:dcc dentry name(?):"my_hugepage_file" flags: 0x17ffffc00000c1(locked|waiters|head|node=0|zone=2|lastcpupid=0x1fffff) page_type: f4(hugetlb) page dumped because: still mapped when deleted CPU: 1 UID: 0 PID: 395 Comm: hugetlb Not tainted 6.17.0-rc5-00044-g7aac71907bde-dirty #484 NONE Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015 Call Trace: <TASK> dump_stack_lvl+0x4f/0x70 filemap_unaccount_folio+0xc4/0x1c0 __filemap_remove_folio+0x38/0x1c0 filemap_remove_folio+0x41/0xd0 remove_inode_hugepages+0x142/0x250 hugetlbfs_fallocate+0x471/0x5a0 vfs_fallocate+0x149/0x380
Hold folio lock before checking if the folio is mapped to avold race with migration.
Which versions are affected by CVE-2025-40006?
How do I fix CVE-2025-40006?
Apply the vendor's patch.
Is CVE-2025-40006 being exploited?
There is no known exploitation of CVE-2025-40006 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2025-40006, DEBIAN-CVE-2025-40006, GHSA-3f8h-q5gp-rc64, ROOT-OS-DEBIAN-11-CVE-2025-40006, ROOT-OS-DEBIAN-12-CVE-2025-40006, ROOT-OS-DEBIAN-13-CVE-2025-40006 and 2 more.