CVE-2025-40039: linux kernel — Fix

Description

In the Linux kernel, the following vulnerability has been resolved: ksmbd: Fix race condition in RPC handle list access The 'sess->rpc_handle_list' XArray manages RPC handles within a ksmbd session. Access to this list is intended to be protected by 'sess->rpc_lock' (an rw_semaphore). However, the locking implementation was flawed, leading to potential race conditions. In ksmbd_session_rpc_open(), the code incorrectly acquired only a read lock before calling xa_store() and xa_erase(). Since these operations modify the XArray structure, a write lock is required to ensure exclusive access and prevent data corruption from concurrent modifications. Furthermore, ksmbd_session_rpc_method() accessed the list using xa_load() without holding any lock at all. This could lead to reading inconsistent data or a potential use-after-free if an entry is concurrently removed and the pointer is dereferenced. Fix these issues by: 1. Using down_write() and up_write() in ksmbd_session_rpc_open() to ensure exclusive access during XArray modification, and ensuring the lock is correctly released on error paths. 2. Adding down_read() and up_read() in ksmbd_session_rpc_method() to safely protect the lookup.

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CVSS v3.1 Score

4.7

MEDIUM

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

Weakness Type (CWE)

CWE-362 CWE-362

Affected Products

Vendor	Product	Versions
linux	linux_kernel	5.15.145 — 5.16
linux	linux_kernel	6.1.71 — 6.2
linux	linux_kernel	6.3 — 6.6.123
linux	linux_kernel	6.7 — 6.12.53
linux	linux_kernel	6.13 — 6.17.3

References

Advisories & Patches

https://git.kernel.org/stable/c/305853cce379407090a73b38c5de5ba748893aee https://git.kernel.org/stable/c/5cc679ba0f4505936124cd4179ba66bb0a4bd9f3 https://git.kernel.org/stable/c/69674b029002b1d90b655f014bdf64f404efa54d https://git.kernel.org/stable/c/6b615a8fb3af0baf8126cde3d4fee97d57222ffc https://git.kernel.org/stable/c/6bd7e0e55dcea2cf0d391bbc21c2eb069b4be3e1

Frequently Asked Questions

What is CVE-2025-40039? +

In the Linux kernel, the following vulnerability has been resolved: ksmbd: Fix race condition in RPC handle list access The 'sess->rpc_handle_list' XArray manages RPC handles within a ksmbd session. Access to this list is intended to be protected by 'sess->rpc_lock' (an rw_semaphore). However, the locking implementation was flawed, leading to potential race conditions. In ksmbd_session_rpc_open(), the code incorrectly acquired only a read lock before calling xa_store() and xa_erase(). Since these operations modify the XArray structure, a write lock is required to ensure exclusive access and prevent data corruption from concurrent modifications. Furthermore, ksmbd_session_rpc_method() accessed the list using xa_load() without holding any lock at all. This could lead to reading inconsistent data or a potential use-after-free if an entry is concurrently removed and the pointer is dereferenced. Fix these issues by: 1. Using down_write() and up_write() in ksmbd_session_rpc_open() to ensure exclusive access during XArray modification, and ensuring the lock is correctly released on error paths. 2. Adding down_read() and up_read() in ksmbd_session_rpc_method() to safely protect the lookup. It has a CVSS v3.1 base score of 4.7 (MEDIUM).

How severe is CVE-2025-40039? +

CVE-2025-40039 has a CVSS v3.1 score of 4.7 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.

What products are affected by CVE-2025-40039? +

CVE-2025-40039 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-40039? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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