CVE-2026-93159 in Linux
Summary
by MITRE • 09/18/2026
In the Linux kernel, the following vulnerability has been resolved:
crypto: atmel-sha204a - fix heap info leak on I2C transfer failure
The nonblocking RNG path allocates a work_data structure to track the state of an in-flight asynchronous I2C request. This pointer is stored in rng->priv and later consumed by the read path once the transaction completes.
If the underlying I2C transfer fails, the completion callback is invoked with a non-zero status. In this case, the allocated work_data is not usable for producing RNG output and must not remain associated with the hwrng state.
Previously, the failure path only logged a warning but left the pointer state uncleared, which can result in subsequent read attempts observing stale state and interpreting it as valid completion data.
Fix this by freeing the pending work_data. The I2C transaction reports an error. This ensures that failed requests do not leave residual state behind that could be interpreted as valid RNG data on later reads. Clearing rng->priv is done at the subsequent call to nonblocking read.
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Analysis
by VulDB Data Team • 09/18/2026
The Linux kernel cryptographic subsystem contains a vulnerability within the Atmel SHA204A hardware random number generator driver, specifically affecting the handling of asynchronous I2C transfers when they fail. This issue stems from improper memory management and state cleanup in the non-blocking random number generation path. The driver utilizes a work_data structure to track the status of ongoing asynchronous requests, storing a pointer to this allocation within the rng->priv field for later retrieval by the read callback upon transaction completion. Under normal operational conditions where I2C transfers succeed, this mechanism functions correctly as the state is properly consumed and cleared after use. However, when an underlying I2C transfer encounters an error condition, the driver invokes a completion callback with a non-zero status code indicating failure. In these scenarios, the allocated work_data structure becomes invalid for producing random number output because the transaction did not complete successfully.
The critical technical flaw lies in the error handling path of this asynchronous operation. Previously, when an I2C transfer failed, the driver would log a warning message but critically neglected to free the pending work_data allocation or clear the rng->priv pointer. This oversight results in a stale state being retained within the hardware random number generator structure. Consequently, subsequent attempts to read from the RNG may encounter this residual data and incorrectly interpret it as valid completion information for a new request. Because the memory containing the stale work_data is not immediately released back to the system allocator upon failure, it remains accessible until potentially overwritten or freed by other kernel operations, creating an opportunity for information disclosure.
This vulnerability constitutes an out-of-bounds read scenario where uninitialized or stale heap data can be exposed to userspace applications requesting random numbers. From a classification perspective, this aligns with CWE-200: Information Exposure and CWE-415: Double Free if the subsequent handling attempts to free the same pointer again after it was already leaked in state. The attack vector allows an attacker who has access to the /dev/hwrng device node or equivalent interface to potentially extract sensitive kernel memory contents that were previously allocated for I2C transaction tracking. This information leak can aid further exploitation by revealing internal kernel structures, pointers, or other data that could compromise system security integrity.
The operational impact of this vulnerability is primarily centered on confidentiality rather than availability or integrity in the immediate sense, although it degrades the quality and trustworthiness of generated random numbers if stale state influences output selection. An attacker leveraging this flaw can perform information gathering attacks against the kernel memory space. To mitigate this risk, the fix involves ensuring that when an I2C transfer fails, the pending work_data is properly freed to prevent resource leaks and residual state retention. Additionally, clearing the rng->priv pointer at the subsequent call to the non-blocking read function ensures that any attempt to access stale data results in a null reference or proper error handling rather than interpreting garbage memory as valid RNG output. System administrators should apply kernel updates containing this patch immediately to close this information disclosure channel and maintain the integrity of cryptographic operations dependent on hardware random number generation.