CVE-2026-80951i3c: master: svc: bound IBI payload to the requested max_payload_len

Official description

In the Linux kernel, the following vulnerability has been resolved: i3c: master: svc: bound IBI payload to the requested max_payload_len svc_i3c_master_handle_ibi() reads the IBI payload from the RX FIFO into the IBI slot. The loop is bounded by the hardware FIFO size (SVC_I3C_FIFO_SIZE), not by the slot size. slot->data points into the IBI pool, which i3c_generic_ibi_alloc_pool() sizes at max_payload_len per slot. svc_i3c_master_request_ibi() only rejects a max_payload_len larger than SVC_I3C_FIFO_SIZE, so a driver can request a smaller one. mctp-i3c requests 1. Each readsb() then copies the controller RXCOUNT bytes (up to 31) with no check against the slot size. A device that sends more bytes than the slot holds writes past slot->data, an out-of-bounds write into the IBI pool. Bound the loop by dev->ibi->max_payload_len and clamp each read to the space left in the slot, the same way dw-i3c does. A device can still send more than the requested payload. Flush the leftover bytes from the RX FIFO so they do not leak into the next transfer.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/7c099b0b292a68d0ef558527945dbfb756fbf893
• https://git.kernel.org/stable/c/7cc5ba756bc1cfffab9cb2695742f9f479dc73f7
• https://git.kernel.org/stable/c/35aa6730b8c5626b879a4e893fe664f59bf07d7f
• https://git.kernel.org/stable/c/f296a0d5907bf88314dfda67245f7f69d1552470
• https://git.kernel.org/stable/c/5697d779577e2786ff3348ae9b77020ac0cf0aab
• https://git.kernel.org/stable/c/aac3c5aababc7fb69d5bf5b0cc52d308574e3a8c
• https://git.kernel.org/stable/c/e2bda39d7f9f285ec803e200b5c1f17143d0b483