ovl: fix double end_creating() on the casefold-mismatch path

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-89767
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-11 20:20:07 UTC
Updated2026-09-11 20:20:07 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: ovl: fix double end_creating() on the casefold-mismatch path ovl_create_real() releases the new dentry twice when the casefold consistency check fails. The S_IFDIR branch calls end_creating() and sets err, then falls through to the common out: label which calls end_creating() on the same dentry again: case S_IFDIR: newdentry = ovl_do_mkdir(ofs, dir, newdentry, attr->mode); err = PTR_ERR_OR_ZERO(newdentry); if (!err && ofs->casefold != ovl_dentry_casefolded(newdentry)) { pr_warn_ratelimited(...); end_creating(newdentry); /* first */ err = -EINVAL; } break; ... if (err) goto out; ... out: if (err) { end_creating(newdentry); /* second, same dentry */ return ERR_PTR(err); } end_creating() is end_dirop(), which does inode_unlock() on the parent and dput() on the dentry, so the parent directory's i_rwsem is unlocked twice and the dentry is put twice. The second unlock releases a lock that is not held, which is what wedges every later creation under that parent, and the second dput() drops a reference that was never taken. The branch was added by commit dfc7da402ccc ("ovl: Check for casefold consistency when creating new dentries") as a bare dput(), which already released the reference twice; commit fe497f0759e0 ("VFS: change vfs_mkdir() to unlock on failure.") converted both sites to end_creating(), adding the double unlock. This is reachable by an unprivileged user. The casefold consistency of the layers is validated at mount time in ovl_parse_layer(), and again on every lookup in ovl_lookup_single(), but ofs->workdir is the internal "work" subdirectory created inside the user-supplied workdir, and that subdirectory is not re-checked. Marking it casefolded after the mount therefore makes every ovl_create_temp() inherit the wrong state - and that path reaches ovl_create_real() through ovl_start_creating_temp(), which uses start_creating() with a generated name and so never runs the lookup-time check. unshare -Urm mount -t tmpfs -o casefold=utf8-12.1.0 tmpfs mnt mkdir -p mnt/lower/d mnt/upper mnt/work mnt/merged mount -t overlay ovl -o lowerdir=mnt/lower,\ upperdir=mnt/upper,workdir=mnt/work mnt/merged chattr +F mnt/work/work mkdir mnt/merged/d/sub # directory copy-up overlayfs: wrong inherited casefold (work/#5) and the next copy-up blocks forever on the parent's i_rwsem: mkdir D start_creating+0x65/0xb0 ovl_start_creating_temp+0xb0/0xe0 [overlay] ovl_create_temp+0xa3/0x1d0 [overlay] ovl_copy_up_one+0x1f1c/0x21c0 [overlay] ovl_copy_up_flags+0xf5/0x140 [overlay] ovl_create_object+0xb7/0x220 [overlay] ovl_mkdir+0x23/0x40 [overlay] Drop the end_creating() from the branch and let out: own the cleanup, which is what every other error path in this function already does.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected dfc7da402ccc92d6e4b01a4778a3f15f2496b9af 2fa220bc0f84597cb6de665e5b5021c5901ddf00 git Not specified
CNA Linux Linux affected dfc7da402ccc92d6e4b01a4778a3f15f2496b9af b1aa8ab78a8e87aee9e306971465408e059f839a git Not specified
CNA Linux Linux affected dfc7da402ccc92d6e4b01a4778a3f15f2496b9af 077ab8985ee278c3d8618182d335b0f0cd919e16 git Not specified
CNA Linux Linux affected 6.18 Not specified
CNA Linux Linux unaffected 6.18 semver Not specified
CNA Linux Linux unaffected 6.18.51 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.4 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/2fa220bc0f84597cb6de665e5b5021c5901ddf00 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/b1aa8ab78a8e87aee9e306971465408e059f839a 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/077ab8985ee278c3d8618182d335b0f0cd919e16 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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