Linux Kernel up to 7.2.11 readdir iterate_dir locking

Summaryinfo

A vulnerability classified as critical has been found in Linux Kernel up to 7.2.11. Affected is the function iterate_dir of the component readdir. This manipulation causes locking. The identification of this vulnerability is CVE-2026-99084. The attack can only be executed locally. There is no exploit available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability classified as critical was found in Linux Kernel up to 7.2.11. Affected by this vulnerability is the function iterate_dir of the component readdir. The manipulation with an unknown input leads to a locking vulnerability. The CWE definition for the vulnerability is CWE-667. The product does not properly acquire or release a lock on a resource, leading to unexpected resource state changes and behaviors. As an impact it is known to affect availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: readdir: take no inode lock on an immutable directory iterate_dir() takes the directory's i_rwsem shared and holds it across ->iterate_shared(). For a directory that never has an entry and is never removed the lock keeps nothing still, it only orders every reader and every writer of that inode behind each other. For the directory of a nullfs instance that matters. The instance of the initial mount namespace is the root of every empty mount namespace and the private instance is the root of every kernel thread, so one inode is shared across users who have nothing else in common. And a reader can hold the lock for as long as it likes: back the getdents() buffer with a mapping of a file on a FUSE mount of your own, let the copy of "." and ".." fault and let the server wait. Queue an exclusive taker behind it, a mkdir() in that directory goes through start_dirop() before the read-only mount is reported, and from then on every lookup that misses the dcache in that directory, every create and every mount on it waits until the server answers. One user of an empty mount namespace stalls all the others. Add FOP_IMMUTABLE for the file operations of a directory that never changes and is never removed and let iterate_dir() skip the lock for it. The flag never changes for a file, ->f_pos is protected by f_pos_lock since directories are FMODE_ATOMIC_POS, IS_DEADDIR can't be set on such a directory and neither touch_atime() nor fsnotify take i_rwsem. Set it on the nullfs directory. The placeholder directories of libfs never have an entry either but their owners remove them, so they keep the lock.

The advisory is shared at git.kernel.org. This vulnerability is known as CVE-2026-99084 since 09/25/2026. The exploitation appears to be easy. An attack has to be approached locally. Technical details are known, but no exploit is available.

Upgrading to version 7.2.12 eliminates this vulnerability. Applying the patch 6d30b399ae28e5166d62484f81ccaefde6fe7996/e08f57a7dcb83818c058e415988c23beb6c5a47f is able to eliminate this problem. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.2.0
• 7.2.1
• 7.2.2
• 7.2.3
• 7.2.4
• 7.2.5
• 7.2.6
• 7.2.7
• 7.2.8
• 7.2.9
• 7.2.10
• 7.2.11

License

• open-source

Website

• Vendor: https://www.kernel.org/

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Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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