{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-89767","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2026-09-11T19:38:34.764Z","datePublished":"2026-09-11T19:47:07.353Z","dateUpdated":"2026-09-13T06:34:10.053Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-09-13T06:34:10.053Z"},"descriptions":[{"lang":"en","value":"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 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."}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - The bug is in overlayfs ovl_create_real() on the S_IFDIR casefold-mismatch path, reached from local mkdir/creat copy-up (ovl_mkdir → ovl_create_object → ovl_copy_up_one → ovl_create_temp). An unprivileged user can mount overlay on tmpfs in a user+mount namespace; this is not a network packet path.\nAC:L - The attacker fully controls the overlay mount, the post-mount chattr +F on the internal work/ workdir, and the mkdir that forces directory copy-up. The mismatch is deterministic with no race or victim state beyond the attacker's control.\nPR:L - Overlayfs sets FS_USERNS_MOUNT, so a normal local user can unshare a user and mount namespace, mount overlay, and reach ovl_create_real without init-namespace root. The commit's unshare -Urm reproducer matches this unprivileged path.\nUI:N - The attacker mounts the overlay, marks the internal workdir casefolded, and issues mkdir themselves. No separate victim action is required.\nS:U - Double end_creating() corrupts kernel VFS locking and dentry references on the local host. This stays within the kernel's security authority and is not a VM escape, IOMMU bypass, or other cross-boundary impact.\nC:H - end_creating() is end_dirop(), which inode_unlock()s the parent and dput()s the dentry. The extra dput can free or underflow a still-used dentry, and the extra unlock corrupts i_rwsem so concurrent VFS operations can race, enabling kernel memory disclosure.\nI:H - Double dput plus double inode_unlock of the parent i_rwsem break directory serialization and dentry lifetime. That enables use-after-free and unsynchronized create/lookup on the workdir, a high-integrity kernel memory-corruption primitive.\nA:H - The extra unlock leaves the workdir i_rwsem corrupt so later copy-up/create sleeps uninterruptibly in D state, and the extra dput/UAF can oops or panic the kernel. Either outcome is high availability impact."}]}],"affected":[{"product":"Linux","vendor":"Linux","defaultStatus":"unaffected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/overlayfs/dir.c"],"versions":[{"version":"dfc7da402ccc92d6e4b01a4778a3f15f2496b9af","lessThan":"2fa220bc0f84597cb6de665e5b5021c5901ddf00","status":"affected","versionType":"git"},{"version":"dfc7da402ccc92d6e4b01a4778a3f15f2496b9af","lessThan":"b1aa8ab78a8e87aee9e306971465408e059f839a","status":"affected","versionType":"git"},{"version":"dfc7da402ccc92d6e4b01a4778a3f15f2496b9af","lessThan":"077ab8985ee278c3d8618182d335b0f0cd919e16","status":"affected","versionType":"git"}]},{"product":"Linux","vendor":"Linux","defaultStatus":"affected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/overlayfs/dir.c"],"versions":[{"version":"6.18","status":"affected"},{"version":"0","lessThan":"6.18","status":"unaffected","versionType":"semver"},{"version":"6.18.51","lessThanOrEqual":"6.18.*","status":"unaffected","versionType":"semver"},{"version":"7.2.4","lessThanOrEqual":"7.2.*","status":"unaffected","versionType":"semver"},{"version":"7.3-rc1","lessThanOrEqual":"*","status":"unaffected","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.18","versionEndExcluding":"6.18.51"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.18","versionEndExcluding":"7.2.4"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.18","versionEndExcluding":"7.3-rc1"}]}]}],"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"}],"title":"ovl: fix double end_creating() on the casefold-mismatch path","x_generator":{"engine":"bippy-1.2.0"}}}}