CVE-2026-98886 in Linux
Summary
by MITRE • 10/23/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/gma500: return errors from Oaktrail HDMI I2C reads
xfer_read() waits for the HDMI I2C transaction to reach I2C_TRANSACTION_DONE, but it ignores both timeout and signal returns from wait_for_completion_interruptible_timeout(). If the interrupt never advances the transaction state, the loop can wait forever.
Return -ETIMEDOUT when the completion wait expires, propagate interrupted waits, and make the I2C master_xfer callback return the first transfer error instead of reporting a successful message count.
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Analysis
by VulDB Data Team • 10/23/2026
The vulnerability identified in the Linux kernel's drm/gma500 driver for Oaktrail HDMI interfaces represents a classic resource exhaustion flaw stemming from improper handling of asynchronous completion events. The core technical issue resides within the xfer_read function, which is responsible for managing I2C transactions over the High-Definition Multimedia Interface bus. This function relies on wait_for_completion_interruptible_timeout to block execution until the hardware signals that the transaction has reached a completed state via the I2C_TRANSACTION_DONE flag. However, the original implementation fails to inspect the return value of this waiting mechanism. Consequently, if the underlying hardware or driver logic encounters an error and never transitions the transaction state to done, the loop will persist indefinitely. This lack of timeout handling transforms what should be a transient hardware stall into a permanent system hang, effectively creating a denial-of-service condition for any process attempting to interact with the HDMI I2C bus through this specific driver path.
From a security perspective, this flaw aligns directly with CWE-400, which describes resources not being properly controlled, leading to resource exhaustion. In practical operational terms, an attacker or even a malfunctioning peripheral device could trigger this code path by initiating an I2C read operation that fails to complete due to hardware faults, signal interference, or maliciously crafted input sequences designed to exploit the driver's state machine. The result is a kernel thread stuck in an uninterruptible sleep state for an indefinite period. This not only freezes the specific subsystem but can also impact system stability if other components depend on timely responses from this I2C bus. Furthermore, because the function does not propagate signal interruptions properly, it may prevent user-space processes from being terminated gracefully via standard signals like SIGKILL when they are blocked waiting for this hardware operation to finish.
The remediation strategy implemented in the resolved version addresses these deficiencies by enforcing strict error propagation and timeout enforcement. The updated code now checks the return value of wait_for_completion_interruptible_timeout, ensuring that if the time limit expires without a successful completion signal, the function returns -ETIMEDOUT rather than continuing to loop. Additionally, it correctly handles cases where the wait is interrupted by signals, returning appropriate error codes instead of proceeding with potentially invalid data or states. Crucially, the I2C master_xfer callback has been modified to return the first encountered transfer error immediately, rather than reporting a successful message count despite underlying failures. This ensures that higher-level drivers and user-space applications are promptly notified of the failure, allowing them to handle the error condition gracefully instead of hanging or operating on stale data.
This fix reinforces adherence to robust driver development practices recommended by industry standards such as CWE-754 for improper check for unusual or exceptional conditions. By ensuring that all asynchronous operations have defined timeouts and proper signal handling, the kernel maintains its resilience against both accidental hardware faults and potential malicious exploitation attempts aimed at causing denial of service. The ATT&CK framework categorizes this type of vulnerability under techniques related to resource exhaustion, specifically within the context of local privilege escalation or system availability impact if exploited in conjunction with other vulnerabilities. Properly managing these low-level I2C interactions is essential for maintaining the integrity and stability of embedded systems that rely on Linux kernel drivers for hardware communication.