Medium [CVE-2026-72142] fix locked bus on SMBus block-read of 0 (atomic)
This medium-severity Red Hat Linux advisory covers CVE-2026-72142 affecting Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat package: kernel-rt.
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Summary
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. When an I2C slave device performs an SMBus block-read operation with a byte count of zero, the atomic (polling) path in the driver fails to properly release the I2C bus.
This can cause the bus to become stuck, requiring a power cycle of the I2C controller to restore functionality. This issue leads to a denial of service for the affected system.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · medium-confidence parse· fetched 24 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · medium-confidence parse· fetched 24 days ago·verify at source
Mitigation
The source record does not include mitigation steps. That is not a statement that no fix exists — read the vendor advisory below for the authoritative guidance.
Official advisory · medium-confidence parse· fetched 24 days ago·verify at source
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