CVE-2026-98990 — namespace: check a submount for references right before unmounting it

Affected: Linux

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

namespace: check a submount for references right before unmounting it

shrink_submounts() and mark_mounts_for_expiry() first collect all the mounts they are allowed to unmount and then unmount them.

Whether a mount is busy is decided by propagate_mount_busy() on the tree. But unmounting the first mount changes the tree that the second one propagates into. propagate_umount() moves a surviving overmount off a copy it unmounts and mounts it where the copy was mounted. If that's where the propagated copy of the second victim is looked up the overmount becomes a candidate of the second umount_tree(). It's childless and so trim_one() commits it without looking at its reference count.

So a synchronous umount pulls out a busy mount that is in use somewhere else and marks it MNT_SYNC_UMOUNT while it has users:

umount2(/tmp/plshrink/p1, 0) = 0 errno 0 cwd is (unreachable)

The same two umounts requested one after the other fail with EBUSY. This needs a mount with MNT_SHRINKABLE, i.e., automounted submounts of NFS, AFS and CIFS or the tracefs mount below debugfs. Bind mounts inherit the flag.

Check each mount right before it is unmounted under the same hold of namespace_sem and mount_lock as the umount itself. Make sure that the algorithm stays linear.

USN-9018-1 — linux, linux-aws, linux-gcp, linux-ibm, linux-oem-7.0, linux-oracle vulnerabilities

Affected: Ubuntu:26.04:LTS: linux, Ubuntu:26.04:LTS: linux-aws, Ubuntu:26.04:LTS: linux-gcp, Ubuntu:26.04:LTS: linux-ibm, Ubuntu:26.04:LTS: linux-oem-7.0, Ubuntu:26.04:LTS: linux-oracle

Several security issues were discovered in the Linux kernel. An attacker could possibly use these to compromise the system. This update corrects flaws in the following subsystems: - Network file systems library; - Stream parser; - ARM64 architecture; - PowerPC architecture; - RISC-V architecture; - S390 architecture; - User-Mode Linux (UML); - x86 architecture; - Block layer subsystem; - Android drivers; - Bluetooth drivers; - TPM device driver; - DPLL subsystem; - EDAC drivers; - GPIO subsystem; - GPU drivers; - HID subsystem; - IIO subsystem; - IIO ADC drivers; - InfiniBand drivers; - Input Device (Miscellaneous) drivers; - Multiple devices driver; - MemoryStick subsystem; - MMC subsystem; - MTD block device drivers; - Network drivers; - Ethernet bonding driver; - Mellanox network drivers; - STMicroelectronics network drivers; - Ethernet team driver; - MediaTek network drivers; - NVME drivers; - Device tree and open firmware driver; - Power sequencing drivers; - Voltage and Current Regulator drivers; - Real Time Clock drivers; - SCSI subsystem; - Greybus lights staging drivers; - Trusted Execution Environment drivers; - Thunderbolt and USB4 drivers; - TTY drivers; - Cadence USB3 driver; - USB Device Class drivers; - USB core drivers; - DesignWare USB2 driver; - DesignWare USB3 driver; - USB Gadget drivers; - USB Serial drivers; - USB Mass Storage drivers; - USB Type-C suppor…

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CVE-2026-98990 — namespace: check a submount for references right before unmounting it

USN-9018-1 — linux, linux-aws, linux-gcp, linux-ibm, linux-oem-7.0, linux-oracle vulnerabilities