CVE-2026-72034

Summary

In the Linux kernel, the following vulnerability has been resolved:

fhandle: reject detached mounts in capable_wrt_mount()

The recent fhandle RCU fix moved the mount namespace capability check into capable_wrt_mount(), so a non-NULL mnt_namespace survives the ns_capable() dereference. The helper still assumes the later READ_ONCE(mount->mnt_ns) must be non-NULL because may_decode_fh() checked is_mounted() first.

That assumption is not stable. A detached mount from open_tree(…, OPEN_TREE_CLONE) can be dissolved on fput while open_by_handle_at() is between those checks, and umount_tree() can clear mount->mnt_ns. If the helper observes NULL, it dereferences mnt_ns->user_ns and panics.

Return false when the RCU read observes a detached mount. This keeps the relaxed permission path conservative: a mount no longer attached to a namespace cannot authorize open_by_handle_at() access.

Affected Software

VendorProductVersion RangeStatus
LinuxLinux620c266f394932e5decc4b34683a75dfc59dc2f4 < 15104234c267ebe04b9f9a73e5c2179cc265ff60affected
LinuxLinux620c266f394932e5decc4b34683a75dfc59dc2f4 < 6c52226072a3c61337b1eec1799bb987748884faaffected
LinuxLinux620c266f394932e5decc4b34683a75dfc59dc2f4 < 6ee183d89261bf1d1cf9f06d80a40dab8f36ee55affected
LinuxLinux620c266f394932e5decc4b34683a75dfc59dc2f4 < 6c732471740bc2ac9b0946134f9f551dc75f4369affected
LinuxLinux6.11affected
LinuxLinux0 < 6.11unaffected
LinuxLinux6.12.97 <= 6.12.*unaffected
LinuxLinux6.18.40 <= 6.18.*unaffected
LinuxLinux7.1.5 <= 7.1.*unaffected
LinuxLinux7.2 <= *unaffected

Weaknesses

References