mm/gup: fix FOLL_FORCE COW security issue and remove FOLL_COW

Summary

CVE	CVE-2022-50014
State	PUBLISHED
Assigner	Linux
Source Priority	CVE Program / NVD first with legacy fallback
Published	2025-06-18 11:15:29 UTC
Updated	2026-08-04 10:18:03 UTC
Description	In the Linux kernel, the following vulnerability has been resolved: mm/gup: fix FOLL_FORCE COW security issue and remove FOLL_COW Ever since the Dirty COW (CVE-2016-5195) security issue happened, we know that FOLL_FORCE can be possibly dangerous, especially if there are races that can be exploited by user space. Right now, it would be sufficient to have some code that sets a PTE of a R/O-mapped shared page dirty, in order for it to erroneously become writable by FOLL_FORCE. The implications of setting a write-protected PTE dirty might not be immediately obvious to everyone. And in fact ever since commit 9ae0f87d009c ("mm/shmem: unconditionally set pte dirty in mfill_atomic_install_pte"), we can use UFFDIO_CONTINUE to map a shmem page R/O while marking the pte dirty. This can be used by unprivileged user space to modify tmpfs/shmem file content even if the user does not have write permissions to the file, and to bypass memfd write sealing -- Dirty COW restricted to tmpfs/shmem (CVE-2022-2590). To fix such security issues for good, the insight is that we really only need that fancy retry logic (FOLL_COW) for COW mappings that are not writable (!VM_WRITE). And in a COW mapping, we really only broke COW if we have an exclusive anonymous page mapped. If we have something else mapped, or the mapped anonymous page might be shared (!PageAnonExclusive), we have to trigger a write fault to break COW. If we don't find an exclusive anonymous page when we retry, we have to trigger COW breaking once again because something intervened. Let's move away from this mandatory-retry + dirty handling and rely on our PageAnonExclusive() flag for making a similar decision, to use the same COW logic as in other kernel parts here as well. In case we stumble over a PTE in a COW mapping that does not map an exclusive anonymous page, COW was not properly broken and we have to trigger a fake write-fault to break COW. Just like we do in can_change_pte_writable() added via commit 64fe24a3e05e ("mm/mprotect: try avoiding write faults for exclusive anonymous pages when changing protection") and commit 76aefad628aa ("mm/mprotect: fix soft-dirty check in can_change_pte_writable()"), take care of softdirty and uffd-wp manually. For example, a write() via /proc/self/mem to a uffd-wp-protected range has to fail instead of silently granting write access and bypassing the userspace fault handler. Note that FOLL_FORCE is not only used for debug access, but also triggered by applications without debug intentions, for example, when pinning pages via RDMA. This fixes CVE-2022-2590. Note that only x86_64 and aarch64 are affected, because only those support CONFIG_HAVE_ARCH_USERFAULTFD_MINOR. Fortunately, FOLL_COW is no longer required to handle FOLL_FORCE. So let's just get rid of it. Thanks to Nadav Amit for pointing out that the pte_dirty() check in FOLL_FORCE code is problematic and might be exploitable. Note 1: We don't check for the PTE being dirty because it doesn't matter for making a "was COWed" decision anymore, and whoever modifies the page has to set the page dirty either way. Note 2: Kernels before extended uffd-wp support and before PageAnonExclusive (< 5.19) can simply revert the problematic commit instead and be safe regarding UFFDIO_CONTINUE. A backport to v5.19 requires minor adjustments due to lack of vma_soft_dirty_enabled().

Risk And Classification

Primary CVSS: v3.1 7 HIGH from [email protected]

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

EPSS: 0.001530000 probability, percentile 0.049850000 (date 2026-08-05)

Problem Types: CWE-362

Version	Source	Type	Score	Severity	Vector
3.1	[email protected]	Primary	7	HIGH	`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H`
3.1	416baaa9-dc9f-4396-8d5f-8c081fb06d67	Secondary	7.8	HIGH	`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`
3.1	CNA	DECLARED	7.8	HIGH	`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`

CVSS v3.1 Breakdown

Attack Vector

Local

Attack Complexity

High

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

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

NVD Known Affected Configurations (CPE 2.3)

Type	Vendor	Product	Version	Update	Edition	Language
Operating System	Linux	Linux Kernel	All	All	All	All
Operating System	Linux	Linux Kernel	6.0	rc1	All	All
Operating System	Linux	Linux Kernel	6.0	rc2	All	All

Vendor Declared Affected Products

Source	Vendor	Product	Version	Platforms
CNA	Linux	Linux	affected 9ae0f87d009ca6c4aab2882641ddfc319727e3db 9def52eb10baab3b700858003d462fcf17d62873 git	Not specified
CNA	Linux	Linux	affected 9ae0f87d009ca6c4aab2882641ddfc319727e3db 5535be3099717646781ce1540cf725965d680e7b git	Not specified
CNA	Linux	Linux	affected 5.16	Not specified
CNA	Linux	Linux	unaffected 5.16 semver	Not specified
CNA	Linux	Linux	unaffected 5.19.6 5.19.* semver	Not specified
CNA	Linux	Linux	unaffected 6.0 * original_commit_for_fix	Not specified

References

Reference	Source	Link	Tags
git.kernel.org/stable/c/5535be3099717646781ce1540cf725965d680e7b	416baaa9-dc9f-4396-8d5f-8c081fb06d67	git.kernel.org	Patch
git.kernel.org/stable/c/9def52eb10baab3b700858003d462fcf17d62873	416baaa9-dc9f-4396-8d5f-8c081fb06d67	git.kernel.org	Patch
CVE Program record	CVE.ORG	www.cve.org	canonical
NVD vulnerability detail	NVD	nvd.nist.gov	canonical, analysis

No vendor comments have been submitted for this CVE.

There are currently no legacy QID mappings associated with this CVE.