GHSA-ghm4-78mm-8v2c: Out-of-bounds write in the ADI MAX32 ADC driver due to incorrect adc_sequence buffer size validation

The ADC API requires each driver to reject a sampling sequence whose destination buffer is too small: the buffersize field of struct adcsequence in include/zephyr/drivers/adc.h documents that "the driver must ensure that samples are not written beyond the limit and it must return an error if the buffer turns out to be not large enough". The ADI MAX32 driver did not honour that contract. startread() in drivers/adc/adcmax32.c compared buffersize, a byte count, against a sample count ((1 + extrasamplings) channels), ignoring sizeof(uint16t), so it accepted a buffer half the required size. The samples are then stored through the uint16t data->buffer by WrapMXCADCGetData(), which writes two bytes per sample and advances the pointer by one uint16t: in adcmax32startchannel() for synchronous reads, and in adcmax32isr() for asynchronous ones. A sequence selecting two channels with a two-byte buffer, for example, passes the check and has its second sample written past the end of the buffer.

On a build with CONFIGUSERSPACE, adcread() and adcreadasync() are system calls. The handler in drivers/adc/adchandlers.c copies the sequence in from user memory, verifies only that [buffer, buffer + buffersize) is writable by the calling thread, and rejects a user-supplied options->callback; it deliberately leaves the size arithmetic to the driver. A user-mode thread that has been granted access to a MAX32 ADC device object therefore fully controls channels, buffer, buffersize and options->extrasamplings, and can make the driver write twice as many bytes as its buffer holds. Because the check scales with extrasamplings, the overrun equals the length of the buffer itself, up to channels 65536 bytes past its end, since the sample pointer is only rewound on a repeat sampling, never on the extra samplings of a sequence.

The resulting stores are performed by the driver in kernel mode (in the system call itself, the ADC context timer, or the ADC interrupt handler for asynchronous reads), where the MPU does not restrict the thread's memory domain, so the write walks linearly out of the user partition and into adjacent memory such as other partitions, kernel data or thread stacks. The impact is kernel-memory corruption of attacker-chosen length at an attacker-chosen offset, a plausible privilege-escalation and denial-of-service primitive from an unprivileged user-mode thread. Builds without CONFIGUSERSPACE are affected only as a caller-side robustness defect, since the application itself supplies the buffer.

The fix replaces that check in startread() with a call to the new shared helper adcsequencevalidatebuffer() in drivers/adc/adccommon.c, passing sizeof(uint16t) as the sample size. The helper computes activechannels sizeof(uint16t) (1 + extrasamplings) and returns -ENOMEM before any sampling is started.