CVE-2025-38311 in Linux
Summary
by MITRE • 07/10/2025
In the Linux kernel, the following vulnerability has been resolved:
iavf: get rid of the crit lock
Get rid of the crit lock. That frees us from the error prone logic of try_locks.
Thanks to netdev_lock() by Jakub it is now easy, and in most cases we were protected by it already - replace crit lock by netdev lock when it was not the case.
Lockdep reports that we should cancel the work under crit_lock [splat1],
and that was the scheme we have mostly followed since [1] by Slawomir.
But when that is done we still got into deadlocks [splat2]. So instead
we should look at the bigger problem, namely "weird locking/scheduling" of the iavf. The first step to fix that is to remove the crit lock. I will followup with a -next series that simplifies scheduling/tasks.
Cancel the work without netdev lock (weird unlock+lock scheme), to fix the [splat2] (which would be totally ugly if we would kept
the crit lock).
Extend protected part of iavf_watchdog_task() to include scheduling more work.
Note that the removed comment in iavf_reset_task() was misplaced, it belonged to inside of the removed if condition, so it's gone now.
[splat1] - w/o this patch - The deadlock during VF removal:
WARNING: possible circular locking dependency detected sh/3825 is trying to acquire lock: ((work_completion)(&(&adapter->watchdog_task)->work)){+.+.}-{0:0}, at: start_flush_work+0x1a1/0x470
but task is already holding lock: (&adapter->crit_lock){+.+.}-{4:4}, at: iavf_remove+0xd1/0x690 [iavf]
which lock already depends on the new lock.
[splat2] - when cancelling work under crit lock, w/o this series,
see [2] for the band aid attempt
WARNING: possible circular locking dependency detected sh/3550 is trying to acquire lock: ((wq_completion)iavf){+.+.}-{0:0}, at: touch_wq_lockdep_map+0x26/0x90
but task is already holding lock: (&dev->lock){+.+.}-{4:4}, at: iavf_remove+0xa6/0x6e0 [iavf]
which lock already depends on the new lock.
[1] fc2e6b3b132a ("iavf: Rework mutexes for better synchronisation")
[2] https://github.com/pkitszel/linux/commit/52dddbfc2bb60294083f5711a158a
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Analysis
by VulDB Data Team • 12/07/2025
The vulnerability described in CVE-2025-38311 affects the Linux kernel's iavf driver, specifically addressing a critical locking mechanism issue that could lead to system instability and potential deadlock conditions. This flaw resides within the Intel Adaptive Virtual Function driver implementation, which manages virtual functions for Intel Ethernet adapters. The root cause involves the removal of a critical lock mechanism known as crit_lock, which was previously used to protect certain operations but introduced complexity and error-prone logic into the driver's synchronization model. The vulnerability demonstrates characteristics consistent with CWE-667, which addresses improper locking scenarios in software systems.
The technical implementation of this vulnerability stems from the problematic use of try_lock mechanisms and the complex interplay between different locking primitives within the driver's codebase. The iavf driver previously relied on crit_lock for protecting specific sections of code, but this approach created circular dependency issues that could result in system deadlocks. The locking dependency chain identified in splat1 shows a scenario where the watchdog_task work completion lock attempts to acquire a lock while already holding the crit_lock, creating a circular dependency that the kernel's lockdep subsystem detects and reports as a potential deadlock. Similarly, splat2 reveals another deadlock scenario where work queue completion locks conflict with device lock dependencies when work cancellation occurs under the crit_lock protection.
The operational impact of this vulnerability extends beyond simple system stability concerns to potentially affect network virtualization environments where iavf drivers are deployed. When the driver encounters conditions that trigger the problematic locking sequence, it can result in complete system hangs or kernel oops situations that require manual intervention to resolve. The fix implemented addresses this by replacing the crit_lock with the netdev_lock, which provides more appropriate and consistent protection where it was previously lacking. This change aligns with established best practices for kernel driver development and follows the pattern established by Jakub's netdev_lock implementation, which offers better protection while avoiding the complex locking schemes that led to the original issues.
The mitigation strategy involves removing the problematic crit_lock mechanism and reworking the driver's locking approach to rely on more standard and well-understood locking primitives. This approach addresses the immediate deadlock conditions while also laying groundwork for further simplification of the driver's scheduling and task management components. The fix demonstrates adherence to security principles by eliminating error-prone locking patterns and reducing the attack surface for potential deadlock exploitation. The solution also includes extending the protected sections of iavf_watchdog_task() to properly include scheduling operations, ensuring that all relevant activities are adequately protected. This change represents a fundamental improvement to the driver's synchronization model and reduces the likelihood of similar issues occurring in the future, aligning with ATT&CK techniques that focus on system stability and resource management. The removal of the misplaced comment in iavf_reset_task() further demonstrates the comprehensive nature of this fix, addressing not just the primary locking issue but also cleaning up code artifacts that could contribute to confusion or future problems.