CVE-2026-89725

In the Linux kernel, the following vulnerability has been resolved:

media: cec: stm32: prevent out-of-bounds write on RX overflow

stm32 rx done() appends each received CEC byte to rx msg.msg[] using rx msg.len as the write index, incrementing it on every RXBR (receive-byte-ready) interrupt without checking it against the buffer size:

cec->rx msg.msg[cec->rx msg.len++] = val & 0xFF;

rx msg.msg[] is a fixed CEC MAX MSG SIZE (16) byte array in struct cec msg, and rx msg.len is only reset on RXACKE/RXOVR or after a completed message (RXEND). The number of bytes received before RXEND is decided by the remote CEC device (it sets EOM), not by the driver. A peer that keeps sending bytes without ending the message drives RXBR repeatedly, pushing rx msg.len past 16 and writing peer-controlled bytes out of bounds into the surrounding memory. This is reachable in normal operation once the driver has probed and receiving is enabled, from the IRQ thread, without any local privilege.

The length check in the CEC core runs on the consumer side, after the byte has been stored, so it does not prevent the overflow. Bound the index in the driver before the store, as the other platform CEC drivers already do (e.g. tegra cec), dropping the excess bytes of an overlong frame.

Found by static analysis tool CodeQL.