Medium [CVE-2026-53170] reject DMA commands with uninitialized length

In the Linux kernel, the following vulnerability has been resolved: accel/ethosu: reject DMA commands with uninitialized length cmd_state_init() initializes the command state with memset(0xff), leaving dma->len at U64_MAX to signal missing setup.

The only setter is NPU_SET_DMA0_LEN; if userspace omits this command and issues NPU_OP_DMA_START, dma->len remains U64_MAX. In dma_length(), a positive stride added to U64_MAX wraps to a small value.

With size0 == 1, check_mul_overflow() does not trigger and dma_length() returns 0 instead of U64_MAX. The caller's U64_MAX check then passes, region_size[] stays 0, and the bounds check in ethosu_job.c is bypassed, allowing hardware to execute DMA with stale physical addresses.

Fix by checking for U64_MAX at the start of dma_length() before any arithmetic, consistent with the sentinel value used throughout the driver to detect uninitialized fields. A local attacker could exploit a vulnerability where DMA commands with uninitialized length are not properly handled.

By omitting a specific DMA length setup command and issuing a DMA start command, a user could bypass bounds checks, allowing the hardware to execute DMA operations with stale physical addresses. This could lead to memory corruption, potentially resulting in privilege escalation or arbitrary code execution.

Red Hat severity: Moderate. Weakness: CWE-190.