The ADC API requires each driver to reject a sampling sequence whose destination buffer is too small: the buffer_size field of struct adc_sequence 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. start_read() in drivers/adc/adc_max32.c compared buffer_size, a byte count, against a sample count ((1 + extra_samplings) channels), ignoring sizeof(uint16_t), so it accepted a buffer half the required size. The samples are then stored through the uint16_t data->buffer by Wrap_MXC_ADC_GetData(), which writes two bytes per sample and advances the pointer by one uint16_t: in adc_max32_start_channel() for synchronous reads, and in adc_max32_isr() 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 CONFIG_USERSPACE, adc_read() and adc_read_async() are system calls. The handler in drivers/adc/adc_handlers.c copies the sequence in from user memory, verifies only that [buffer, buffer + buffer_size) 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, buffer…