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Date: Tue, 14 Nov 2023 19:03:38 -0800 From: Kees Cook <keescook@...omium.org> To: "Gustavo A. R. Silva" <gustavoars@...nel.org> Cc: Jean Delvare <jdelvare@...e.com>, Guenter Roeck <linux@...ck-us.net>, Joel Stanley <joel@....id.au>, Andrew Jeffery <andrew@...econstruct.com.au>, linux-hwmon@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linux-aspeed@...ts.ozlabs.org, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH v2][next] hwmon: (aspeed-pwm-tacho) Fix -Wstringop-overflow warning in aspeed_create_fan_tach_channel() On Tue, Nov 14, 2023 at 01:53:08PM -0600, Gustavo A. R. Silva wrote: > Based on the documentation below, the maximum number of Fan tach > channels is 16: > > Documentation/devicetree/bindings/hwmon/aspeed-pwm-tacho.txt:45: > 45 - aspeed,fan-tach-ch : should specify the Fan tach input channel. > 46 integer value in the range 0 through 15, with 0 indicating > 47 Fan tach channel 0 and 15 indicating Fan tach channel 15. > 48 At least one Fan tach input channel is required. > > However, the compiler doesn't know that, and legitimaly warns about a potential > overwrite in array `u8 fan_tach_ch_source[16]` in `struct aspeed_pwm_tacho_data`, > in case `index` takes a value outside the boundaries of the array: > > drivers/hwmon/aspeed-pwm-tacho.c: > 179 struct aspeed_pwm_tacho_data { > ... > 184 bool fan_tach_present[16]; > ... > 193 u8 fan_tach_ch_source[16]; > 196 }; > > In function ‘aspeed_create_fan_tach_channel’, > inlined from ‘aspeed_create_fan’ at drivers/hwmon/aspeed-pwm-tacho.c:877:2, > inlined from ‘aspeed_pwm_tacho_probe’ at drivers/hwmon/aspeed-pwm-tacho.c:936:9: > drivers/hwmon/aspeed-pwm-tacho.c:751:49: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=] > 751 | priv->fan_tach_ch_source[index] = pwm_source; > | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~ > drivers/hwmon/aspeed-pwm-tacho.c: In function ‘aspeed_pwm_tacho_probe’: > drivers/hwmon/aspeed-pwm-tacho.c:193:12: note: at offset [48, 255] into destination object ‘fan_tach_ch_source’ of size 16 > 193 | u8 fan_tach_ch_source[16]; > | ^~~~~~~~~~~~~~~~~~ > > Fix this by sanity checking `index` before using it to index arrays of > size 16 elements in `struct aspeed_pwm_tacho_data`. Also, pass `dev` as > argument to function `aspeed_create_fan_tach_channel()`, and add an error > message in case `index` is out-of-bounds, in which case return `-EINVAL`. > > Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org> Thanks for the v2! This looks good; it's able to pass back the error now. Reviewed-by: Kees Cook <keescook@...omium.org> -- Kees Cook
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