CVE-2026-98981 — namespace: unhash a dentry before detaching the mounts on it

Affected: Linux

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

namespace: unhash a dentry before detaching the mounts on it

unlink(), rmdir() and rename() remove the entry from the filesystem, call detach_mounts() on the entry with the inode locked and then call d_delete() once the inode is unlocked.

The thing is that between detach_mounts() and d_delete() the dentry is still hashed and positive. But after detach_mounts() nothing covers the dentry anymore. A lookup that finds this dentry in the dcache can uncover what the mounts hid.

That's a problem when unlinking files or directories that are mountpoints in other mount namespaces. Everybody who had the underlying entry covered can race the detach_mount() call until d_delete() has run.

The race window isn't all that small. It encompasses namespace_unlock() with a full synchronize_rcu_expedited() grace period and the inode_unlock() of the entry.

In my experiments three walkers that kept trying read an overmounted file in 11938 of the 16140 unlinks that removed its mountpoint from a bind mount of the filesystem within a minute.

Fun fact, d_invalidate() has the same ordering problem but gets it right. It unhashes the dentry first and detaches the mounts afterwards. Let's do the same in __detach_mounts():

- A lookup that hasn't found the dentry yet misses it in the dcache and waits for the directory lock that the caller holds until the name is gone for good.

- A lockless lookup that found it already fails the…

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-2026-98981 — namespace: unhash a dentry before detaching the mounts on it

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