CVE-2026-89767
CVE-2026-89767 is a security vulnerability. O3 Security confirms whether CVE-2026-89767 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
In 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…
Description
In 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.
Detection & mitigation playbook
VulnerabilityDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for the affected component. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Remediation status
No patched version of the affected component has shipped for CVE-2026-89767 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
Mitigate without a patch
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-89767 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-89767. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-89767 in your dependencies?
O3 detects CVE-2026-89767 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.