Description (CNA)
In the Linux kernel, the following vulnerability has been resolved: namespace: don't copy an unmounted mount tree may_copy_tree() accepts a mount whose root is an nsfs or pidfs file before it checks whether that mount is mounted. This exception exists for nsfs and pidfs mounts. They are part of no mount namespace so neither check_mnt() nor is_mounted() would let them through and bind-mounting a nsfsfd or a pidfd wouldn't work. Problem is that exception also admits a bind mount of such a file when it was lazily unmounted and is only kept alive by a file descriptor: mount --bind /proc/self/ns/net /tmp/x exec 3< /tmp/x umount -l /tmp/x mount --rbind /proc/self/fd/3 /tmp/y With MS_REC or AT_RECURSIVE copy_tree() doesn't stop at the unmounted mount. It copies every mount that stayed attached to it as well. So if you have a bunch of overmounts over the nsfsfd or the pidfd the whole unmounted stack is copied. That's a bug. So refuse to walk an unmounted tree. Copying its root alone stays possible. So a bind mount of a namespace that is gone can still be recreated from a file descriptor on the old one. The file descriptor pins that mount and its root and __has_locked_children() only reads the direct children which don't leave the parent's list without namespace_sem. The internal mounts carry MNT_NS_INTERNAL instead of NULL and are still walked. Copying an unmounted tree recursively fails with EINVAL.
Affected (CNA)
| Vendor / product | Versions |
|---|---|
| Linux / Linux | affected e149ed2b805fefdccf7ccdfc19eca22fdd4514ac before 86a2d56b1960720bf1844441c0890621e9db2f25; affected e149ed2b805fefdccf7ccdfc19eca22fdd4514ac before 7e037b1fd339d865737c8accd29abcf40130a5a0; affected e149ed2b805fefdccf7ccdfc19eca22fdd4514ac before b47b40c4f058418f9707454543179df240796aad; affected e149ed2b805fefdccf7ccdfc19eca22fdd4514ac before 8d3527457e183cedee3003c2897314da49488311; affected e149ed2b805fefdccf7ccdfc19eca22fdd4514ac before 8bacbf6be959973b28b691713a872c12eae69eec |
| Linux / Linux | affected 3.19; unaffected 0 before 3.19; unaffected 6.6.160 through 6.6.*; unaffected 6.12.113 through 6.12.*; unaffected 6.18.57 through 6.18.*; unaffected 7.2.11 through 7.2.*; unaffected 7.3 through * |
CWE
No CWE identifiers supplied.
References
- https://git.kernel.org/stable/c/86a2d56b1960720bf1844441c0890621e9db2f25
- https://git.kernel.org/stable/c/7e037b1fd339d865737c8accd29abcf40130a5a0
- https://git.kernel.org/stable/c/b47b40c4f058418f9707454543179df240796aad
- https://git.kernel.org/stable/c/8d3527457e183cedee3003c2897314da49488311
- https://git.kernel.org/stable/c/8bacbf6be959973b28b691713a872c12eae69eec