CVE-2026-90388 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
iommu/dma: Check atomic pool allocation result directly
The non-blocking, non-coherent allocation path uses dma_alloc_from_pool(), which returns the allocated page and fills cpu_addr only on success.
Do not rely on cpu_addr to detect allocation failure in this path. Check the returned page directly before using it for the IOMMU mapping.
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Analysis
by VulDB Data Team • 09/17/2026
The Linux kernel's I/O Memory Management Unit subsystem manages hardware access to physical memory, ensuring that devices can safely interact with system RAM through address translation and protection mechanisms. A critical aspect of this process involves allocating buffers for data transfer between device drivers and peripherals. In scenarios requiring non-blocking operations or dealing with non-coherent architectures, the kernel utilizes a specific allocation path via the dma_alloc_from_pool function. This function is designed to provide memory that can be allocated without sleeping, which is essential for interrupt contexts or other time-sensitive code paths where blocking on memory availability would cause system instability or deadlocks. The technical flaw identified in this subsystem stems from an incorrect assumption regarding how allocation success or failure is signaled by the underlying allocator implementation.
The vulnerability arises because the dma_alloc_from_pool function returns a pointer to the allocated page structure and simultaneously populates a cpu_addr variable with the virtual address of that memory only if the allocation succeeds. In the flawed code path, developers incorrectly relied on checking whether cpu_addr was non-null or valid as an indicator of successful allocation. However, since the documentation and implementation specify that cpu_addr is filled exclusively upon success, relying on it for failure detection creates a logic gap. If the allocation fails due to resource exhaustion or other constraints, the function may return NULL for the page pointer while leaving cpu_addr in an undefined state or potentially retaining stale data from previous operations. By not explicitly checking the returned page pointer before proceeding, the code risks using invalid memory references when allocations fail.
This logical error leads to a significant operational impact characterized by potential kernel crashes, data corruption, and security vulnerabilities. When the IOMMU mapping logic proceeds with an invalid or NULL page reference derived from this unchecked allocation path, it can result in null pointer dereferences that crash the operating system. Furthermore, if stale values are used for address translation, hardware devices might be granted access to incorrect physical memory regions. This misconfiguration violates the fundamental security principle of least privilege and isolation enforced by IOMMU technology, potentially allowing malicious or buggy device drivers to read from or write to arbitrary kernel memory spaces. Such conditions can facilitate information disclosure attacks where sensitive data is leaked through DMA operations, or integrity violations where critical system structures are overwritten, leading to complete compromise of the host environment.
The resolution involves modifying the code to strictly verify the return value of dma_alloc_from_pool before attempting any IOMMU mapping operations. By checking the page pointer directly for NULL or error conditions immediately after allocation, the kernel ensures that only valid, successfully allocated memory is passed to subsequent hardware configuration steps. This change aligns with robust defensive programming practices and prevents the use of uninitialized or invalid pointers in critical security boundaries. To mitigate similar risks across the codebase, developers should adhere strictly to API contracts regarding return values and error codes rather than inferring success from side effects like pointer assignments that are not guaranteed to be updated on failure.
From a standards perspective, this vulnerability corresponds to CWE-252, which describes unchecked return value errors where software fails to check for failure or an unexpected response after calling a function. Additionally, the potential for unauthorized memory access via DMA operations relates closely to CWE-120, buffer overflow without description of size, and CWE-787, out-of-bounds write, depending on how the invalid pointer is utilized by the IOMMU subsystem. In terms of adversarial tactics, this flaw could be leveraged within ATT&CK technique T1059, Command and Scripting Interpreter, if exploited to gain initial execution, or more critically in post-exploitation phases involving T1048, Exfiltration Over Alternative Protocol, by abusing DMA capabilities for data theft. Remediation requires applying the kernel patch that enforces explicit validation of allocation results, ensuring that all IOMMU mappings are established only on verified successful memory allocations to maintain system stability and security integrity.