CVE-2026-90425 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
iommu/tegra241-cmdqv: Require exactly one Stream ID for a vSID
tegra241_vintf_init_vsid() maps a guest vSID to a single physical Stream ID taken from master->streams[0], and only warns when the device does not have
exactly one stream. A device with several streams gets only its first one mapped, so a guest vSID invalidation cannot reach the others' ATC and IOTLB entries; a device with none makes master->streams a ZERO_SIZE_PTR, read out of bounds.
Reject the mapping with -EOPNOTSUPP if master->num_streams is not one.
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Analysis
by VulDB Data Team • 09/17/2026
The vulnerability identified in the Linux kernel's Tegra241 IOMMU driver involves improper validation and handling of Stream IDs during virtualization context initialization, specifically within the tegra241_vintf_init_vsid function. This component is responsible for mapping guest virtual Stream Identifiers to physical hardware Stream IDs, a critical step for ensuring that Input-Output Memory Management Unit operations are correctly routed in virtualized environments. The core technical flaw lies in the driver's assumption regarding device topology and its subsequent handling of edge cases where this assumption does not hold true. Specifically, the code currently attempts to map a guest vSID using only the first entry from the master->streams array, which corresponds to streams[0]. This logic fails to account for devices that utilize multiple Stream IDs or those that possess no valid stream configurations at all, leading to either functional misconfiguration or memory safety violations.
When a device is configured with more than one physical Stream ID, the current implementation restricts the mapping to only the first available stream. Consequently, any invalidation requests issued by the guest for its virtualized context fail to propagate correctly to the Address Translation Cache and Input-Output Translation Lookaside Buffer entries associated with the remaining streams. This partial mapping results in stale or inconsistent translation state within the hardware caches of those unmapped streams. From an operational perspective, this can lead to data corruption, memory access violations, or system instability as devices attempt to perform DMA operations using outdated address translations that do not reflect the current guest context. The security impact is significant because it allows a potentially malicious or misconfigured virtual machine to bypass intended isolation boundaries by exploiting the incomplete invalidation mechanism, effectively maintaining access to physical resources that should have been invalidated or remapped.
The severity of this issue escalates when dealing with devices that report zero active streams. In such scenarios, the master->streams pointer becomes a ZERO_SIZE_PTR, which is a special kernel marker indicating an allocation of size zero rather than NULL. The existing code proceeds to read from this pointer without adequate bounds checking or null-like validation appropriate for this specific type of pointer. This results in out-of-bounds memory access, potentially leading to information disclosure if the adjacent memory contains sensitive data, or more critically, a kernel panic and system crash due to invalid memory dereference. Such vulnerabilities are classified under CWE-125 Out-of-bounds Read and CWE-787 Out-of-bounds Write depending on subsequent usage of the corrupted pointer state, representing fundamental input validation failures in low-level driver code.
To mitigate this vulnerability, the kernel developers have implemented a strict enforcement mechanism that requires exactly one Stream ID for any device attempting to utilize virtualized stream identifiers. The fix involves checking the master->num_streams variable during initialization and rejecting the mapping operation with an -EOPNOTSUPP error if the count does not equal one. This approach ensures that only devices with a predictable, single-stream topology are allowed into the virtualization context, thereby preventing both the partial invalidation issue in multi-stream scenarios and the out-of-bounds read in zero-stream cases. From a defense-in-depth perspective, this aligns with ATT&CK technique T1499 Endpoint Denial of Service by mitigating potential crash vectors that could be triggered via guest interactions. System administrators should ensure their kernel versions are updated to include this patch, and developers integrating custom devices into the Tegra241 platform must verify that device tree configurations strictly adhere to single-stream requirements if virtualization features are enabled.