{"id":"CVE-2026-98987","title":"namespace: look at the topmost mount for a mount namespace file","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: look at the topmost mount for a mount namespace file\n\nattach_recursive_mnt() preallocates a mountpoint for the root of the\ntopmost mount of the source so tha…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 96f5d2e051653f2cfe9137c5d3c7794c358ffb03 < b9c40553f6ceba50042281eef6f701e5fb719726","Linux >= 96f5d2e051653f2cfe9137c5d3c7794c358ffb03 < 87ecd4c6da146363384a603bd9e90c90e7275536","Linux >= 96f5d2e051653f2cfe9137c5d3c7794c358ffb03 < 8714b44adac7b10506e1db3ef1710689751f0f10","Linux 6.17"],"published":"2026-10-23","updated":"2026-10-23","sourceUpdated":"2026-10-23T12:20:06.180Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-98987","references":[{"url":"https://git.kernel.org/stable/c/b9c40553f6ceba50042281eef6f701e5fb719726"},{"url":"https://git.kernel.org/stable/c/87ecd4c6da146363384a603bd9e90c90e7275536"},{"url":"https://git.kernel.org/stable/c/8714b44adac7b10506e1db3ef1710689751f0f10"}],"tags":["cve.org"],"ingestedAt":"2026-10-23T13:24:55.547Z","slug":"CVE-2026-98987","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: look at the topmost mount for a mount namespace file\n\nattach_recursive_mnt() preallocates a mountpoint for the root of the\ntopmost mount of the source so that a mount that already sits at the\ndestination can be put on top of the source or on top of one of its\npropagated copies.\n\nThe copies are made without CL_COPY_MNT_NS_FILE so their chain of\novermounts is shorter than the source's. It ends below the first bind\nmount of a mount namespace file. So while the loop walks up the chain of\nthe source it remembers the mountpoint of that mount in \"shorter\" and\nthe existing mount is put there for the copies.\n\nBut the loop ends at the topmost mount without ever looking at it. If\nthe topmost mount is the only mount namespace file in the chain\n\"shorter\" stays NULL and mnt_change_mountpoint() attaches the existing\nmount of the copy below the root of the mount namespace file. That's a\ndentry of nsfs. No path walk in the copy's mount namespace ever gets\nthere. The mount is gone until its parent goes and the copy that took\nits place can't be unmounted synchronously because it has a child:\n\n  S      bind mount of a file\n  N      bind mount of a mount namespace file on top of S\n  A      shared mount, B a slave of A, Q mounted on B/file\n\n  move_mount(S, A/file)\n  cat B/file          -> the content of S instead of Q\n  umount B/file       -> EBUSY\n\nLook at every mount of the chain including the topmost one.\n\n## Affected\n\n- `Linux >= 96f5d2e051653f2cfe9137c5d3c7794c358ffb03 < b9c40553f6ceba50042281eef6f701e5fb719726`\n- `Linux >= 96f5d2e051653f2cfe9137c5d3c7794c358ffb03 < 87ecd4c6da146363384a603bd9e90c90e7275536`\n- `Linux >= 96f5d2e051653f2cfe9137c5d3c7794c358ffb03 < 8714b44adac7b10506e1db3ef1710689751f0f10`\n- `Linux 6.17`\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":[]}