{"id":"CVE-2026-98990","title":"namespace: check a submount for references right before unmounting it","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: check a submount for references right before unmounting it\n\nshrink_submounts() and mark_mounts_for_expiry() first collect all the\nmounts they are allowed to …","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 1064f874abc0d05eeed8993815f584d847b72486 < f6394281834492c6516a405a348b545ae698a331","Linux >= 1064f874abc0d05eeed8993815f584d847b72486 < 6e4012e571867868b545c91ca9d6095fdb709907","Linux >= 1064f874abc0d05eeed8993815f584d847b72486 < d73f04e92c1aab78d96ac6cadb234c8a3a373d22","Linux >= 1064f874abc0d05eeed8993815f584d847b72486 < 18902a23ef36f83d32bafc58ae2484e6bb4bb8ef","Linux >= 1064f874abc0d05eeed8993815f584d847b72486 < 32bf92416614a1e3ff3524fc6b780259c7aad3ef","Linux 5e6ef5ef6eaf690faad3a7c6c665ebf45d7b6ccf","Linux 839d42687dfce0ed0ea2c6bd8d707cc0e276fbe7","Linux 808e83e5add13152bd4a88346487de68395c136b","Linux 6de9d08a9718ee9c12ba6343c50141c2d633e3dc","Linux >= 4.1.40 < 4.2","Linux >= 4.4.54 < 4.5","Linux >= 4.9.15 < 4.10","Linux >= 4.10.3 < 4.11","Linux 4.11"],"published":"2026-10-23","updated":"2026-10-23","sourceUpdated":"2026-10-23T12:20:09.349Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-98990","references":[{"url":"https://git.kernel.org/stable/c/f6394281834492c6516a405a348b545ae698a331"},{"url":"https://git.kernel.org/stable/c/6e4012e571867868b545c91ca9d6095fdb709907"},{"url":"https://git.kernel.org/stable/c/d73f04e92c1aab78d96ac6cadb234c8a3a373d22"},{"url":"https://git.kernel.org/stable/c/18902a23ef36f83d32bafc58ae2484e6bb4bb8ef"},{"url":"https://git.kernel.org/stable/c/32bf92416614a1e3ff3524fc6b780259c7aad3ef"}],"tags":["cve.org"],"ingestedAt":"2026-10-23T13:24:55.545Z","slug":"CVE-2026-98990","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: check a submount for references right before unmounting it\n\nshrink_submounts() and mark_mounts_for_expiry() first collect all the\nmounts they are allowed to unmount and then unmount them.\n\nWhether a mount is busy is decided by propagate_mount_busy() on the\ntree. But unmounting the first mount changes the tree that the second\none propagates into. propagate_umount()\nmoves a surviving overmount off a copy it unmounts and mounts it where\nthe copy was mounted. If that's where the propagated copy of the second\nvictim is looked up the overmount becomes a candidate of the second\numount_tree(). It's childless and so trim_one() commits it without\nlooking at its reference count.\n\nSo a synchronous umount pulls out a busy mount that is in use somewhere\nelse and marks it MNT_SYNC_UMOUNT while it has users:\n\n  umount2(/tmp/plshrink/p1, 0) = 0 errno 0\n  cwd is (unreachable)\n\nThe same two umounts requested one after the other fail with EBUSY.\nThis needs a mount with MNT_SHRINKABLE, i.e., automounted submounts of\nNFS, AFS and CIFS or the tracefs mount below debugfs. Bind mounts\ninherit the flag.\n\nCheck each mount right before it is unmounted under the same hold of\nnamespace_sem and mount_lock as the umount itself. Make sure that the\nalgorithm stays linear.\n\n## Affected\n\n- `Linux >= 1064f874abc0d05eeed8993815f584d847b72486 < f6394281834492c6516a405a348b545ae698a331`\n- `Linux >= 1064f874abc0d05eeed8993815f584d847b72486 < 6e4012e571867868b545c91ca9d6095fdb709907`\n- `Linux >= 1064f874abc0d05eeed8993815f584d847b72486 < d73f04e92c1aab78d96ac6cadb234c8a3a373d22`\n- `Linux >= 1064f874abc0d05eeed8993815f584d847b72486 < 18902a23ef36f83d32bafc58ae2484e6bb4bb8ef`\n- `Linux >= 1064f874abc0d05eeed8993815f584d847b72486 < 32bf92416614a1e3ff3524fc6b780259c7aad3ef`\n- `Linux 5e6ef5ef6eaf690faad3a7c6c665ebf45d7b6ccf`\n- `Linux 839d42687dfce0ed0ea2c6bd8d707cc0e276fbe7`\n- `Linux 808e83e5add13152bd4a88346487de68395c136b`\n- `Linux 6de9d08a9718ee9c12ba6343c50141c2d633e3dc`\n- `Linux >= 4.1.40 < 4.2`\n- `Linux >= 4.4.54 < 4.5`\n- `Linux >= 4.9.15 < 4.10`\n- `Linux >= 4.10.3 < 4.11`\n- `Linux 4.11`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}