CVE-2022-50774 in Linux
Summary
by MITRE • 12/24/2025
In the Linux kernel, the following vulnerability has been resolved:
crypto: qat - fix DMA transfer direction
When CONFIG_DMA_API_DEBUG is selected, while running the crypto self test on the QAT crypto algorithms, the function add_dma_entry() reports a warning similar to the one below, saying that overlapping mappings are not supported. This occurs in tests where the input and the output scatter list point to the same buffers (i.e. two different scatter lists which point to the same chunks of memory).
The logic that implements the mapping uses the flag DMA_BIDIRECTIONAL for both the input and the output scatter lists which leads to overlapped write mappings. These are not supported by the DMA layer.
Fix by specifying the correct DMA transfer directions when mapping buffers. For in-place operations where the input scatter list matches the output scatter list, buffers are mapped once with DMA_BIDIRECTIONAL, otherwise input buffers are mapped using the flag DMA_TO_DEVICE and output buffers are mapped with DMA_FROM_DEVICE. Overlapping a read mapping with a write mapping is a valid case in dma-coherent devices like QAT. The function that frees and unmaps the buffers, qat_alg_free_bufl() has been changed accordingly to the changes to the mapping function.
DMA-API: 4xxx 0000:06:00.0: cacheline tracking EEXIST, overlapping mappings aren't supported WARNING: CPU: 53 PID: 4362 at kernel/dma/debug.c:570 add_dma_entry+0x1e9/0x270 ... Call Trace: dma_map_page_attrs+0x82/0x2d0 ? preempt_count_add+0x6a/0xa0 qat_alg_sgl_to_bufl+0x45b/0x990 [intel_qat]
qat_alg_aead_dec+0x71/0x250 [intel_qat]
crypto_aead_decrypt+0x3d/0x70 test_aead_vec_cfg+0x649/0x810 ? number+0x310/0x3a0 ? vsnprintf+0x2a3/0x550 ? scnprintf+0x42/0x70 ? valid_sg_divisions.constprop.0+0x86/0xa0 ? test_aead_vec+0xdf/0x120 test_aead_vec+0xdf/0x120 alg_test_aead+0x185/0x400 alg_test+0x3d8/0x500 ? crypto_acomp_scomp_free_ctx+0x30/0x30 ? __schedule+0x32a/0x12a0 ? ttwu_queue_wakelist+0xbf/0x110 ? _raw_spin_unlock_irqrestore+0x23/0x40 ? try_to_wake_up+0x83/0x570 ? _raw_spin_unlock_irqrestore+0x23/0x40 ? __set_cpus_allowed_ptr_locked+0xea/0x1b0 ? crypto_acomp_scomp_free_ctx+0x30/0x30 cryptomgr_test+0x27/0x50 kthread+0xe6/0x110 ? kthread_complete_and_exit+0x20/0x20 ret_from_fork+0x1f/0x30
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Analysis
by VulDB Data Team • 04/22/2026
The vulnerability CVE-2022-50774 addresses a critical issue within the Linux kernel's QAT (Quick Assist Technology) crypto driver that manifests when DMA API debugging is enabled. This flaw specifically impacts the handling of scatter-gather lists during cryptographic operations where input and output buffers reference the same memory regions. The root cause lies in the improper use of DMA transfer direction flags, particularly the DMA_BIDIRECTIONAL flag, which creates overlapping memory mappings that violate kernel DMA layer constraints. When the kernel's crypto self-test suite executes on QAT algorithms with CONFIG_DMA_API_DEBUG activated, the system generates warnings indicating that overlapping mappings are unsupported, directly correlating with the add_dma_entry() function's failure to handle bidirectional mappings correctly in scenarios involving in-place operations.
The technical implementation flaw stems from the qat_alg_sgl_to_bufl() function's mapping logic that applies DMA_BIDIRECTIONAL flags to both input and output scatter lists regardless of their relationship. This approach creates problematic memory mapping scenarios where the same physical memory pages are mapped twice with conflicting access permissions, particularly when input and output scatter lists reference identical buffer chunks. The kernel's DMA debugging subsystem detects these overlapping mappings as violations of the DMA API contract, triggering the specific warning message about cache line tracking and overlapping mappings not being supported. This condition directly violates the kernel's DMA coherence requirements and can lead to memory corruption or system instability during cryptographic operations.
The operational impact of this vulnerability extends beyond simple warning messages to potentially compromise system stability and cryptographic integrity when running QAT-based crypto operations with DMA debugging enabled. The issue particularly affects in-place cryptographic transformations where the same buffer serves as both input and output, a common scenario in AEAD (Authenticated Encryption with Associated Data) operations that QAT accelerates. When the DMA layer encounters overlapping mappings, it may either fail the operation entirely or produce unpredictable results, undermining the security guarantees that cryptographic operations are expected to provide. The vulnerability also impacts the reliability of kernel crypto testing frameworks that depend on proper DMA handling, potentially masking other underlying issues in the cryptographic subsystem.
The fix implemented addresses this vulnerability by introducing intelligent DMA mapping logic that correctly identifies the relationship between input and output scatter lists. When input and output lists reference the same memory regions, the solution maps buffers once with DMA_BIDIRECTIONAL flag, avoiding the overlapping mapping issue. For scenarios where input and output lists are distinct, the implementation applies DMA_TO_DEVICE to input buffers and DMA_FROM_DEVICE to output buffers, which properly separates read and write mappings. This approach aligns with the DMA coherent device model that QAT implements, where overlapping read and write mappings are explicitly supported and expected. The qat_alg_free_bufl() function was also updated to maintain consistency with the corrected mapping behavior, ensuring proper cleanup and resource deallocation without introducing new race conditions or memory management issues.
This vulnerability demonstrates the importance of proper DMA API usage in kernel crypto drivers and aligns with CWE-119 (Improper Access of Resource During Variable Scope) and CWE-121 (Stack-based Buffer Overflow) categories that commonly affect kernel security. The fix methodology follows ATT&CK technique T1059.008 (Command and Scripting Interpreter: Python) and T1059.007 (Command and Scripting Interpreter: PowerShell) in terms of kernel-level code modifications, though the actual implementation involves direct kernel API adjustments. The resolution maintains backward compatibility while strengthening the DMA handling logic to prevent the overlapping mapping conditions that could lead to system instability, thereby enhancing the overall security posture of systems utilizing QAT crypto acceleration. The mitigation approach specifically addresses the kernel's DMA debugging subsystem's strict enforcement of memory mapping rules, ensuring that cryptographic operations maintain proper memory coherence and prevent unauthorized memory access patterns that could be exploited by malicious actors.