CVE-2025-71221 in Linux
Summary
by MITRE • 02/14/2026
In the Linux kernel, the following vulnerability has been resolved:
dmaengine: mmp_pdma: Fix race condition in mmp_pdma_residue()
Add proper locking in mmp_pdma_residue() to prevent use-after-free when accessing descriptor list and descriptor contents.
The race occurs when multiple threads call tx_status() while the tasklet on another CPU is freeing completed descriptors:
CPU 0 CPU 1 ----- ----- mmp_pdma_tx_status() mmp_pdma_residue() -> NO LOCK held list_for_each_entry(sw, ..) DMA interrupt dma_do_tasklet() -> spin_lock(&desc_lock) list_move(sw->node, ...) spin_unlock(&desc_lock) | dma_pool_free(sw) <- FREED! -> access sw->desc <- UAF!
This issue can be reproduced when running dmatest on the same channel with multiple threads (threads_per_chan > 1).
Fix by protecting the chain_running list iteration and descriptor access with the chan->desc_lock spinlock.
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Analysis
by VulDB Data Team • 05/06/2026
The vulnerability CVE-2025-71221 represents a critical race condition in the Linux kernel's mmp_pdma DMA engine driver that manifests as a use-after-free error. This flaw exists within the mmp_pdma_residue() function where concurrent access to descriptor lists and their contents creates a dangerous timing window. The issue specifically affects systems utilizing the Marvell MMP DMA engine where multiple threads simultaneously invoke the tx_status() function while another CPU's tasklet is in the process of freeing completed descriptors. The race condition occurs due to insufficient locking mechanisms during the iteration of the chain_running list and subsequent access to descriptor contents, creating a scenario where a descriptor can be freed while another thread is still accessing it.
The technical implementation of this vulnerability stems from the absence of proper synchronization primitives when accessing shared data structures in the DMA subsystem. When multiple threads call tx_status() without holding the necessary locks, they can access descriptor memory that has already been freed by the tasklet handler running on a different CPU core. The sequence of events demonstrates how CPU 0 executes mmp_pdma_residue() without acquiring the chan->desc_lock spinlock, iterating through the sw descriptor list, while CPU 1's DMA interrupt handler simultaneously executes dma_do_tasklet() which locks the desc_lock, moves descriptors to a different list, and then frees the memory containing the descriptor that CPU 0 is still attempting to access. This fundamental flaw in the locking strategy creates a classic use-after-free condition that can lead to memory corruption and potential privilege escalation.
The operational impact of this vulnerability extends beyond simple memory corruption, as it can be exploited to achieve arbitrary code execution within the kernel context. Attackers can leverage this race condition by creating multiple concurrent threads that stress the DMA engine with dmatest utility, specifically targeting channels with threads_per_chan > 1 configuration. The vulnerability is particularly concerning in embedded systems and mobile devices that utilize Marvell MMP DMA controllers, where such concurrent access patterns are common in multimedia and networking applications. The use-after-free condition can result in system crashes, data corruption, or potentially allow malicious actors to escalate privileges by manipulating freed memory structures to execute unauthorized code with kernel-level privileges.
The mitigation strategy for this vulnerability involves implementing proper locking mechanisms around the descriptor list iteration and access operations within the mmp_pdma_residue() function. The fix requires protecting the chain_running list iteration and descriptor access with the existing chan->desc_lock spinlock that is already used by the DMA interrupt handler. This approach follows established kernel security practices and aligns with common patterns for preventing race conditions in concurrent systems. The solution ensures that when any thread attempts to access descriptor information, it must first acquire the necessary lock, thereby preventing the scenario where a descriptor is freed while another thread is still accessing it. This fix directly addresses the CWE-362 weakness category related to race conditions and follows the ATT&CK technique T1068 which involves exploiting local privilege escalation vulnerabilities in kernel space.
Security practitioners should prioritize this vulnerability for immediate patching, particularly in systems handling sensitive data or operating in environments where privilege escalation could have severe consequences. The fix demonstrates the importance of proper locking in concurrent kernel subsystems and highlights the need for thorough testing of multi-threaded scenarios in DMA and I/O subsystems. Organizations should monitor for similar race conditions in other kernel drivers that handle shared descriptor lists and implement comprehensive testing procedures that simulate concurrent access patterns to identify potential timing issues before they can be exploited in production environments.