{"id":"CVE-2026-89767","title":"ovl: fix double end_creating() on the casefold-mismatch path","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\novl: fix double end_creating() on the casefold-mismatch path\n\novl_create_real() releases the new dentry twice when the casefold\nconsistency check fails.  The S_IFDIR br…","severity":"high","cvss":7.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cvssSource":"cna","cwe":["CWE-1341"],"vendor":"Linux","product":"Linux","affected":["Linux >= dfc7da402ccc92d6e4b01a4778a3f15f2496b9af < 2fa220bc0f84597cb6de665e5b5021c5901ddf00","Linux >= dfc7da402ccc92d6e4b01a4778a3f15f2496b9af < b1aa8ab78a8e87aee9e306971465408e059f839a","Linux >= dfc7da402ccc92d6e4b01a4778a3f15f2496b9af < 077ab8985ee278c3d8618182d335b0f0cd919e16","Linux 6.18"],"published":"2026-09-11","updated":"2026-10-19","sourceUpdated":"2026-10-19T08:52:20.802Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-89767","references":[{"url":"https://git.kernel.org/stable/c/2fa220bc0f84597cb6de665e5b5021c5901ddf00"},{"url":"https://git.kernel.org/stable/c/b1aa8ab78a8e87aee9e306971465408e059f839a"},{"url":"https://git.kernel.org/stable/c/077ab8985ee278c3d8618182d335b0f0cd919e16"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89767.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-89767"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2532416"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-89767"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89767"},{"url":"https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89767.mbox"}],"tags":["cve.org","csaf","vex","red-hat","score-dispute"],"epss":0.00173,"epssPercentile":0.06733,"scores":{"cna":7.8,"vendor":5.5},"ingestedAt":"2026-09-14T15:23:07.472Z","slug":"CVE-2026-89767","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\novl: fix double end_creating() on the casefold-mismatch path\n\novl_create_real() releases the new dentry twice when the casefold\nconsistency check fails.  The S_IFDIR branch calls end_creating() and\nsets err, then falls through to the common out: label which calls\nend_creating() on the same dentry again:\n\n\tcase S_IFDIR:\n\t\tnewdentry = ovl_do_mkdir(ofs, dir, newdentry, attr->mode);\n\t\terr = PTR_ERR_OR_ZERO(newdentry);\n\t\tif (!err && ofs->casefold != ovl_dentry_casefolded(newdentry)) {\n\t\t\tpr_warn_ratelimited(...);\n\t\t\tend_creating(newdentry);\t/* first */\n\t\t\terr = -EINVAL;\n\t\t}\n\t\tbreak;\n\t...\n\tif (err)\n\t\tgoto out;\n\t...\n out:\n\tif (err) {\n\t\tend_creating(newdentry);\t/* second, same dentry */\n\t\treturn ERR_PTR(err);\n\t}\n\nend_creating() is end_dirop(), which does inode_unlock() on the parent\nand dput() on the dentry, so the parent directory's i_rwsem is unlocked\ntwice and the dentry is put twice.  The second unlock releases a lock\nthat is not held, which is what wedges every later creation under that\nparent, and the second dput() drops a reference that was never taken.\n\nThe branch was added by commit dfc7da402ccc (\"ovl: Check for casefold\nconsistency when creating new dentries\") as a bare dput(), which already\nreleased the reference twice; commit fe497f0759e0 (\"VFS: change\nvfs_mkdir() to unlock on failure.\") converted both sites to\nend_creating(), adding the double unlock.\n\nThis is reachable by an unprivileged user.  The casefold consistency of\nthe layers is validated at mount time in ovl_parse_layer(), and again on\nevery lookup in ovl_lookup_single(), but ofs->workdir is the internal\n\"work\" subdirectory created inside the user-supplied workdir, and that\nsubdirectory is not re-checked.  Marking it casefolded after the mount\ntherefore makes every ovl_create_temp() inherit the wrong state - and\nthat path reaches ovl_create_real() through ovl_start_creating_temp(),\nwhich uses start_creating() with a generated name and so never runs the\nlookup-time check.\n\n  unshare -Urm\n  mount -t tmpfs -o casefold=utf8-12.1.0 tmpfs mnt\n  mkdir -p mnt/lower/d mnt/upper mnt/work mnt/merged\n  mount -t overlay ovl -o lowerdir=mnt/lower,\\\n        upperdir=mnt/upper,workdir=mnt/work mnt/merged\n  chattr +F mnt/work/work\n  mkdir mnt/merged/d/sub\t\t# directory copy-up\n\n  overlayfs: wrong inherited casefold (work/#5)\n\nand the next copy-up blocks forever on the parent's i_rwsem:\n\n  mkdir           D  start_creating+0x65/0xb0\n                     ovl_start_creating_temp+0xb0/0xe0 [overlay]\n                     ovl_create_temp+0xa3/0x1d0 [overlay]\n                     ovl_copy_up_one+0x1f1c/0x21c0 [overlay]\n                     ovl_copy_up_flags+0xf5/0x140 [overlay]\n                     ovl_create_object+0xb7/0x220 [overlay]\n                     ovl_mkdir+0x23/0x40 [overlay]\n\nDrop the end_creating() from the branch and let out: own the cleanup,\nwhich is what every other error path in this function already does.\n\n## Affected\n\n- `Linux >= dfc7da402ccc92d6e4b01a4778a3f15f2496b9af < 2fa220bc0f84597cb6de665e5b5021c5901ddf00`\n- `Linux >= dfc7da402ccc92d6e4b01a4778a3f15f2496b9af < b1aa8ab78a8e87aee9e306971465408e059f839a`\n- `Linux >= dfc7da402ccc92d6e4b01a4778a3f15f2496b9af < 077ab8985ee278c3d8618182d335b0f0cd919e16`\n- `Linux 6.18`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Vendor advisories\n\n- **Red Hat VEX** · Moderate · updated 2026-09-15 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89767.json)","depth":"twilight","depthScore":43,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[{"seq":224562,"id":"CVE-2026-89767","ts":1792401409238,"field":"cvss","old":"5.5","new":"7.8"},{"seq":224561,"id":"CVE-2026-89767","ts":1792401409238,"field":"severity","old":"medium","new":"high"},{"seq":202952,"id":"CVE-2026-89767","ts":1789403733090,"field":"cvss","old":"7.8","new":"5.5"},{"seq":202951,"id":"CVE-2026-89767","ts":1789403733090,"field":"severity","old":"high","new":"medium"},{"seq":197655,"id":"CVE-2026-89767","ts":1789384318267,"field":"cvss","old":"5.5","new":"7.8"},{"seq":197654,"id":"CVE-2026-89767","ts":1789384318267,"field":"severity","old":"medium","new":"high"},{"seq":183630,"id":"CVE-2026-89767","ts":1789356676175,"field":"cvss","old":"7.8","new":"5.5"},{"seq":183629,"id":"CVE-2026-89767","ts":1789356676175,"field":"severity","old":"high","new":"medium"},{"seq":153656,"id":"CVE-2026-89767","ts":1789285351812,"field":"cvss","old":null,"new":"7.8"},{"seq":153655,"id":"CVE-2026-89767","ts":1789285351812,"field":"severity","old":"none","new":"high"},{"seq":147205,"id":"CVE-2026-89767","ts":1789270201114,"field":"cvss","old":null,"new":"5.5"},{"seq":147204,"id":"CVE-2026-89767","ts":1789270201114,"field":"severity","old":"none","new":"medium"},{"seq":108962,"id":"CVE-2026-89767","ts":1789183729750,"field":"cvss","old":null,"new":"5.5"},{"seq":108961,"id":"CVE-2026-89767","ts":1789183729750,"field":"severity","old":"none","new":"medium"}]}