{"id":"CVE-2026-98990","published":"2026-10-23T13:17:20.980","lastModified":"2026-10-23T13:17:20.980","description":"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 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.","cvssScore":null,"cvssSeverity":null,"cvssVector":null,"cwes":[],"vendors":[],"products":[],"references":[{"url":"https://git.kernel.org/stable/c/18902a23ef36f83d32bafc58ae2484e6bb4bb8ef","tags":[]},{"url":"https://git.kernel.org/stable/c/32bf92416614a1e3ff3524fc6b780259c7aad3ef","tags":[]},{"url":"https://git.kernel.org/stable/c/6e4012e571867868b545c91ca9d6095fdb709907","tags":[]},{"url":"https://git.kernel.org/stable/c/d73f04e92c1aab78d96ac6cadb234c8a3a373d22","tags":[]},{"url":"https://git.kernel.org/stable/c/f6394281834492c6516a405a348b545ae698a331","tags":[]}],"exploitRefs":[],"hasPoc":false,"ai":null}