From: Radu Sabau Date: Wed, 27 May 2026 09:38:39 +0000 (+0300) Subject: iio: adc: ad_sigma_delta: fix clear_pending_event for registerless devices X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=91bc6767a4f55dc470d8a56b55b9f2ea09094efe;p=thirdparty%2Fkernel%2Fstable.git iio: adc: ad_sigma_delta: fix clear_pending_event for registerless devices ad_sigma_delta_clear_pending_event() falls through to the status register read path for devices with has_registers = false and no rdy_gpiod. For such devices, ad_sd_read_reg() skips the address byte entirely and clocks raw MISO bytes with no address phase — making it byte-for-byte identical to reading conversion data. If a pending conversion result is present, this partially consumes it and corrupts the data stream for the subsequent ad_sd_read_reg() call in ad_sigma_delta_single_conversion(). Furthermore, with num_resetclks = 0 on these devices, data_read_len evaluates to 0. If the clocked byte has bit 7 clear, pending_event is set and the code attempts memset(data + 2, 0xff, 0 - 1), overflowing to SIZE_MAX and corrupting the heap. Fix by returning 0 immediately when neither rdy_gpiod nor has_registers is set. This is safe for all current registerless devices: ad7191 and ad7780 (with powerdown GPIO) are reset between conversions by CS deassertion, so there is no stale result to drain; ad7780 (without powerdown GPIO) and max11205 are continuously-converting and cycle ~DRDY at the output data rate regardless of whether the previous result was read, so the next falling edge fires naturally. A future registerless device that holds ~DRDY asserted until data is read would be broken by this early return and would require either num_resetclks set or a rdy-gpio. The same heap corruption is reachable on any device with rdy_gpiod set but num_resetclks = 0: if the GPIO indicates a pending event, the drain path executes memset(data + 2, 0xff, 0 - 1) regardless of has_registers. Add an explicit data_read_len == 0 guard after the pending event check; the stale result is then consumed by the first ad_sd_read_reg() call in ad_sigma_delta_single_conversion(). Fixes: 132d44dc6966 ("iio: adc: ad_sigma_delta: Check for previous ready signals") Signed-off-by: Radu Sabau Cc: Signed-off-by: Jonathan Cameron --- diff --git a/drivers/iio/adc/ad_sigma_delta.c b/drivers/iio/adc/ad_sigma_delta.c index 651ade67ad2e..1b410291da53 100644 --- a/drivers/iio/adc/ad_sigma_delta.c +++ b/drivers/iio/adc/ad_sigma_delta.c @@ -262,11 +262,25 @@ static int ad_sigma_delta_clear_pending_event(struct ad_sigma_delta *sigma_delta /* * Read R̅D̅Y̅ pin (if possible) or status register to check if there is an - * old event. + * old event. For devices with neither an RDY GPIO nor registers, + * ad_sd_read_reg() transmits no address byte and clocks raw MISO bytes, + * which is indistinguishable from reading conversion data and would + * partially consume a pending result. Skip the check for such devices. + * + * This is safe for all current registerless devices: ad7191 and ad7780 + * (with powerdown GPIO) are reset between conversions by CS deassertion, + * so there is no stale result to drain; ad7780 (without powerdown GPIO) + * and max11205 are continuously-converting and cycle ~DRDY at the output + * data rate regardless of whether the previous result was read, so the + * next falling edge fires naturally. + * + * A future registerless device that holds ~DRDY asserted until data is + * read would be broken by this early return and would need either + * num_resetclks set or a rdy-gpio. */ if (sigma_delta->rdy_gpiod) { pending_event = gpiod_get_value(sigma_delta->rdy_gpiod); - } else { + } else if (sigma_delta->info->has_registers) { unsigned int status_reg; ret = ad_sd_read_reg(sigma_delta, AD_SD_REG_STATUS, 1, &status_reg); @@ -274,11 +288,24 @@ static int ad_sigma_delta_clear_pending_event(struct ad_sigma_delta *sigma_delta return ret; pending_event = !(status_reg & AD_SD_REG_STATUS_RDY); + } else { + return 0; } if (!pending_event) return 0; + /* + * With num_resetclks = 0, data_read_len is 0 and the drain sequence + * below would compute memset(data + 2, 0xff, 0 - 1), underflowing to + * SIZE_MAX and corrupting the heap. There is no safe way to drain the + * stale result without knowing the data register size; it will be + * consumed by the first ad_sd_read_reg() call in + * ad_sigma_delta_single_conversion(). + */ + if (!data_read_len) + return 0; + /* * In general the size of the data register is unknown. It varies from * device to device, might be one byte longer if CONTROL.DATA_STATUS is