{"id":"CVE-2026-98979","title":"namespace: refuse an automount below a mount that is in no namespace","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: refuse an automount below a mount that is in no namespace\n\nIt's possible to add autmounts even when the parent mount isn't in the\nmount namespace of the call…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= df820f8de4e481222b17f9bcee7b909ae8167529 < 95fb7c259b86f5521f04973040ad492f2bef6f82","Linux >= df820f8de4e481222b17f9bcee7b909ae8167529 < 35f2013f83ef16f9f0331c4c3a8e8d161580d574","Linux >= df820f8de4e481222b17f9bcee7b909ae8167529 < 494c57572d2d5bc2839553ed41aabe92ed0f587c","Linux >= df820f8de4e481222b17f9bcee7b909ae8167529 < 776e20e4fdc23c23687b511ffdc80047878049d3","Linux >= df820f8de4e481222b17f9bcee7b909ae8167529 < ba985ce08471c555af2a2fbe217c1bc2e72a6d8c","Linux 5.8"],"published":"2026-10-23","updated":"2026-10-23","sourceUpdated":"2026-10-23T12:19:52.523Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-98979","references":[{"url":"https://git.kernel.org/stable/c/95fb7c259b86f5521f04973040ad492f2bef6f82"},{"url":"https://git.kernel.org/stable/c/35f2013f83ef16f9f0331c4c3a8e8d161580d574"},{"url":"https://git.kernel.org/stable/c/494c57572d2d5bc2839553ed41aabe92ed0f587c"},{"url":"https://git.kernel.org/stable/c/776e20e4fdc23c23687b511ffdc80047878049d3"},{"url":"https://git.kernel.org/stable/c/ba985ce08471c555af2a2fbe217c1bc2e72a6d8c"}],"tags":["cve.org"],"ingestedAt":"2026-10-23T13:24:55.549Z","slug":"CVE-2026-98979","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: refuse an automount below a mount that is in no namespace\n\nIt's possible to add autmounts even when the parent mount isn't in the\nmount namespace of the caller. The only requirement we have is that the\nparent mount namespace must not be NULL, i.e., unmounted.\n\nProblem is that clone_private_mount() has MNT_NS_INTERNAL which makes\nthat trivially true. So that passes the test and attach_recursive_mnt()\naccepts that as a mount point and funny enough, count_mounts()\ndereferences MNT_NS_INTERNAL. The problem is it is an error pointer...\n\nSo we can reach this in userspace via fanotify. A filesystem mark on the\nlower filesystem of an overlay reports paths on the layer clone and\nreading the event hands out a descriptor on it. For example with debugfs\nas the lower layer it goes kaboom:\n\n  openat(evfd, \"tracing\", O_DIRECTORY)\n\n  Oops: general protection fault\n  KASAN: null-ptr-deref in range [0x1d0-0x1d7]\n  RIP: 0010:count_mounts+0x35/0x200\n   attach_recursive_mnt\n   finish_automount\n\nAnd since that sleeping beauty happens under namespace_sem held for\nwriting every mount operation on the system blocks from then on.\nCongrats.\n\nUse is_mounted() instead which rejects unmounted and internal mounts\nalike. The open fails with EINVAL just as it did before\nclone_private_mount() used MNT_NS_INTERNAL.\n\n## Affected\n\n- `Linux >= df820f8de4e481222b17f9bcee7b909ae8167529 < 95fb7c259b86f5521f04973040ad492f2bef6f82`\n- `Linux >= df820f8de4e481222b17f9bcee7b909ae8167529 < 35f2013f83ef16f9f0331c4c3a8e8d161580d574`\n- `Linux >= df820f8de4e481222b17f9bcee7b909ae8167529 < 494c57572d2d5bc2839553ed41aabe92ed0f587c`\n- `Linux >= df820f8de4e481222b17f9bcee7b909ae8167529 < 776e20e4fdc23c23687b511ffdc80047878049d3`\n- `Linux >= df820f8de4e481222b17f9bcee7b909ae8167529 < ba985ce08471c555af2a2fbe217c1bc2e72a6d8c`\n- `Linux 5.8`\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":[]}