unicode: free the map after a grace period

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-99180
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-28 11:17:38 UTC
Updated2026-10-31 13:17:58 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: unicode: free the map after a grace period generic_ci_d_hash() and generic_ci_d_compare() read sb->s_encoding and dereference the unicode map while a pathwalk in rcu mode holds nothing but rcu_read_lock(). The filesystems that use them, ext4, f2fs and tmpfs, drop the map with utf8_unload() from ->put_super(), which runs when the last reference to the mount goes away. A lookup that is still inside such a filesystem at that point reads a freed map. With a pathwalk held up in utf8_casefold_hash() while the last reference to a casefolded tmpfs goes away: BUG: KASAN: slab-use-after-free in utf8nlookup+0x74c/0x950 Read of size 8 at addr ff110001030fe658 by task walker/98 Call Trace: <TASK> utf8nlookup+0x74c/0x950 utf8byte+0x160/0x1560 utf8_casefold_hash+0x167/0x230 generic_ci_d_hash+0xdd/0x1c0 link_path_walk+0x11ad/0x1d30 path_lookupat+0x63/0xb00 filename_lookup+0x1f1/0x5b0 vfs_statx+0xd7/0x3b0 [...] Allocated by task 94: __kmalloc_cache_noprof+0x249/0x560 utf8_load+0x4e/0x570 shmem_parse_opt_casefold.isra.0+0x92/0x270 [...] Freed by task 97: kfree+0x1db/0x5b0 shmem_put_super+0x72/0x170 generic_shutdown_super+0x14c/0x530 kill_anon_super+0x3a/0x60 deactivate_locked_super+0x9c/0xf0 cleanup_mnt+0x9f/0x130 So far that has been hard to hit. umount(2) waits for a grace period in namespace_unlock() before it drops the mount, so only a mount whose last reference goes away elsewhere, like the close of a file or a chdir out of a lazily unmounted directory, can race a walker. So it is reachable. Delay the free until a grace period has passed. The map and the data table it holds a reference to then outlive any pathwalk that found the superblock before the mount went away. The reference on the data table module is dropped from the rcu callback as well. utf8-core is built in whenever CONFIG_UNICODE is set, so there is no module exit that would have to wait for the callbacks. Overlayfs points the s_encoding of an overlay at the map of its first layer without taking a reference of its own. That stays correct. The layer is held by the overlay, so its map is dropped only after the overlay is gone.

Risk And Classification

Primary CVSS: v3.1 7.8 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

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

EPSS: 0.001830000 probability, percentile 0.079290000 (date 2026-10-31)

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
3.1CNADECLARED7.8HIGHCVSS: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
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected b886ee3e778ec2ad43e276fd378ab492cf6819b7 092e14e1479a39157ca01668d43e4649793f39ed git Not specified
CNA Linux Linux affected b886ee3e778ec2ad43e276fd378ab492cf6819b7 6472455f2b015cad43adb790cb63fe1d3cff2f57 git Not specified
CNA Linux Linux affected b886ee3e778ec2ad43e276fd378ab492cf6819b7 f96c2731a105d6663c606388f5dc21781e00ade5 git Not specified
CNA Linux Linux affected b886ee3e778ec2ad43e276fd378ab492cf6819b7 5d7687b0b71601cc32f1bfd62f56cf5eea3e5a07 git Not specified
CNA Linux Linux affected b886ee3e778ec2ad43e276fd378ab492cf6819b7 69a0d6b31d05e856c7335509222f25321e3c69ca git Not specified
CNA Linux Linux affected b886ee3e778ec2ad43e276fd378ab492cf6819b7 2b54d3c971a1e5df3c9b0bcc10311ae6c29e79d8 git Not specified
CNA Linux Linux affected b886ee3e778ec2ad43e276fd378ab492cf6819b7 6560c3d9a6925e3747d9ad8463e16010c31ba715 git Not specified
CNA Linux Linux affected b886ee3e778ec2ad43e276fd378ab492cf6819b7 a96c5299bd7305eb984377681eb3222a57376405 git Not specified
CNA Linux Linux affected 5.2 Not specified
CNA Linux Linux unaffected 5.2 semver Not specified
CNA Linux Linux unaffected 5.10.273 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.224 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.191 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.161 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.115 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.59 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.13 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/092e14e1479a39157ca01668d43e4649793f39ed 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/6560c3d9a6925e3747d9ad8463e16010c31ba715 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/f96c2731a105d6663c606388f5dc21781e00ade5 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/5d7687b0b71601cc32f1bfd62f56cf5eea3e5a07 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/2b54d3c971a1e5df3c9b0bcc10311ae6c29e79d8 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/69a0d6b31d05e856c7335509222f25321e3c69ca 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/6472455f2b015cad43adb790cb63fe1d3cff2f57 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/a96c5299bd7305eb984377681eb3222a57376405 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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