{"id":"CVE-2026-87039","published":"2026-11-04T06:17:06.623","lastModified":"2026-11-04T06:17:06.733","description":"The user-mode syscall verifier z_vrfy_i2s_configure() in drivers/i2s/i2s_handlers.c copies the caller's struct i2s_config in from user memory and then, when cfg->frame_clk_freq is 0 (the API's \"unconfigure the stream\" request), jumps straight to z_impl_i2s_configure() without performing the K_SYSCALL_OBJ(config.mem_slab, K_OBJ_MEM_SLAB) ownership/type check or the block_size sanity check. The mem_slab field is a struct k_mem_slab *, so on that path a completely unvalidated, user-chosen pointer reaches driver code that is entitled to trust it as a real kernel object.\n\nAny thread running under CONFIG_USERSPACE that has access to an I2S device object can trigger this with a single i2s_configure() call. Most in-tree drivers special-case frame_clk_freq == 0 and never store the caller's structure, but drivers/i2s/i2s_litex.c does not: i2s_litex_configure() only logs a warning for a mismatched frame clock, then memcpy()s the caller's config into stream->cfg and marks the stream I2S_STATE_READY. A subsequent i2s_trigger() with I2S_TRIGGER_START enables the FIFO interrupt, and the interrupt handlers i2s_litex_isr_rx() / i2s_litex_isr_tx() then call k_mem_slab_alloc() and k_mem_slab_free() on the attacker-supplied pointer in supervisor context.\n\nThe result is an arbitrary-pointer read/write primitive executed by the kernel on behalf of an unprivileged thread — k_mem_slab_alloc() takes a spinlock at slab->lock and reads and writes slab->free_list and the link word inside the returned \"block\" — which defeats the CONFIG_USERSPACE isolation boundary entirely. The same missing validation is a hazard for out-of-tree I2S drivers that retain the configuration on the unconfigure path. Builds without CONFIG_USERSPACE are unaffected, since the verifier is not used.\n\nThe fix zeroes config.mem_slab and config.block_size on the unconfigure path so the driver can never receive an unvalidated pointer, while still allowing a stream to be unconfigured by a caller that does not own a memory slab, as the API documents.","cvssScore":7.8,"cvssSeverity":"HIGH","cvssVector":"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H","cwes":["CWE-787"],"vendors":[],"products":[],"references":[{"url":"https://github.com/zephyrproject-rtos/zephyr/commit/e9898c4d22f69575d9b5f297b3df130ceaff1b8f","tags":[]},{"url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-g43m-x6vj-5cg2","tags":[]}],"exploitRefs":[{"url":"https://github.com/zephyrproject-rtos/zephyr/commit/e9898c4d22f69575d9b5f297b3df130ceaff1b8f","tags":[]},{"url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-g43m-x6vj-5cg2","tags":[]}],"hasPoc":true,"ai":null}