CVE-2026-72142 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
i2c: imx: fix locked bus on SMBus block-read of 0 (atomic)
SMBus 3.1 6.5.7 allows a Block Read byte count of 0, but the atomic (polling) path rejects it as -EPROTO. Worse, it returns without a NACK+STOP: the next receive cycle has already started, so the target keeps holding SDA and the bus stays stuck until a power cycle for this i2c controller.
Reading I2DR to obtain the count likewise arms the next byte on the count > I2C_SMBUS_BLOCK_MAX path, which also returned -EPROTO directly and left the bus held.
Handle both: NACK the in-flight dummy byte (TXAK) and extend msgs->len so the existing last-byte handling emits STOP; the dummy byte is discarded. A count of 0 is a valid empty block read; a count above I2C_SMBUS_BLOCK_MAX is still reported as -EPROTO, but only after the bus has been released.
The interrupt-driven path has the same flaw from a later commit and is fixed separately, as it carries a different Fixes: tag and stable range.
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Analysis
by VulDB Data Team • 08/15/2026
This vulnerability affects the Linux kernel's i2c imx driver implementation specifically within the SMBus block-read functionality. The issue stems from improper handling of zero-length block reads according to SMBus 3.1 specification section 6.5.7, which explicitly permits a Block Read byte count of 0. The atomic polling path in the driver incorrectly rejects such valid requests with -EPROTO error code while failing to properly release the I2C bus. This creates a critical operational failure where the bus remains locked in a stuck state due to the target device holding the SDA line, requiring physical power cycling to recover.
The technical flaw manifests through multiple pathways within the driver's implementation. When processing a zero-byte block read, the code attempts to read from I2DR register to obtain the byte count, which inadvertently triggers the next byte reception cycle before proper error handling can occur. This premature activation of subsequent byte transfers leaves the bus in an inconsistent state where SDA remains asserted by the target device, preventing normal operation until manual intervention. The atomic path specifically fails to send a proper NACK+STOP sequence, leaving the bus in a locked condition that persists until power reset.
The operational impact of this vulnerability is significant for embedded systems and hardware platforms relying on i2c communication with SMBus devices. Systems using the affected imx driver may experience complete communication failures when encountering legitimate zero-length block read requests, which can occur during normal device enumeration or configuration sequences. This affects various automotive, industrial, and consumer electronics applications where SMBus compliance is required. The vulnerability essentially creates a denial-of-service condition that can render I2C controllers unusable until system reboot, with no graceful recovery mechanism available.
The fix implements proper bus state management by ensuring that when a zero-length block read is encountered, the driver sends an appropriate NACK (TXAK) for the in-flight dummy byte and extends the message length to trigger normal STOP condition generation through existing last-byte handling mechanisms. This approach maintains backward compatibility while properly handling the valid edge case of empty block reads. The solution ensures that even though a count of 0 represents a valid empty read, the bus state is properly cleaned up before any error propagation occurs. Additionally, counts exceeding I2C_SMBUS_BLOCK_MAX continue to generate -EPROTO errors but now only after proper bus release, preventing the permanent lock condition.
This vulnerability aligns with CWE-691 weakness category related to insufficient control flow management and represents a specific instance of improper handling of edge cases in protocol implementations. From an ATT&CK perspective, this could be categorized under privilege escalation or denial-of-service techniques when exploited in embedded systems. The fix demonstrates proper error handling principles where resource cleanup occurs before error propagation, preventing resource leaks that could lead to system instability. The separate fix for the interrupt-driven path indicates the vulnerability existed across multiple code execution paths within the same driver component, requiring comprehensive remediation efforts.
The vulnerability highlights critical considerations in embedded driver development where protocol compliance must be balanced with robust error handling and resource management. Modern I2C controllers and SMBus implementations require careful attention to edge cases that may not appear in typical usage patterns but can cause catastrophic failures in production systems. This fix demonstrates the importance of considering all valid protocol states including zero-length operations, which while seemingly trivial, can have substantial operational consequences in hardware communication stacks. The solution approach of extending message length for proper STOP generation rather than modifying core error handling represents a clean architectural fix that maintains existing code behavior while correcting the specific bus state management issue.