Linux Kernel up to 7.2.5 ksmbd __ksmbd_close_fd flc_blocked_requests use after free

Summaryinfo

A vulnerability was found in Linux Kernel up to 7.2.5. It has been classified as very critical. The impacted element is the function __ksmbd_close_fd of the component ksmbd. Performing a manipulation of the argument flc_blocked_requests results in use after free. This vulnerability is reported as CVE-2026-90155. The attack is possible to be carried out remotely. No exploit exists. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability, which was classified as very critical, was found in Linux Kernel up to 7.2.5. This affects the function __ksmbd_close_fd of the component ksmbd. The manipulation of the argument flc_blocked_requests with an unknown input leads to a use after free vulnerability. CWE is classifying the issue as CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: ksmbd: detach blocked lock requests before freeing A file_lock retained by ksmbd for byte-range lock bookkeeping can still be part of the VFS blocked-request graph. In particular, the VFS can chain a new waiter below an already blocked request through flc_blocked_requests. The ksmbd_file reference count does not cover that graph. Both __ksmbd_close_fd() and the cross-request unlock path free these retained file_lock objects directly. If a dependent waiter is still attached, locks_release_private() hits BUG_ON(!list_empty(&flc->flc_blocked_requests)). The same lifetime mismatch can leave a freed ksmbd_lock reachable through its request-local llist. Detach the file_lock from the blocked-request graph before freeing it in the close, cross-request unlock, and rollback paths. locks_delete_block() also wakes requests chained below the object. Remove llist when a completed lock is published so a globally visible ksmbd_lock no longer points into the submitting worker's stack.

The advisory is shared at git.kernel.org. This vulnerability is uniquely identified as CVE-2026-90155 since 09/11/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. Technical details are known, but no exploit is available. The price for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 09/17/2026).

Upgrading to version 7.2.6 or 7.3-rc1 eliminates this vulnerability. Applying the patch 514a0b2bc949963497e66cacd433f65dc768a71d/215e8816b1ac25176d911abb8704390413ccee4b 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

License

• open-source

Website

• Vendor: https://www.kernel.org/

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