On 08/11/2022 18.31, Jason A. Donenfeld wrote: > "If "bytes_read * 8 * rng->quality / 1024" is greater than 0x7FFFFFFF, > the upper bits of the result will all be 1." > > Except "bytes_read" is an int. So false positive. Well, the automated report could use a better wording, but just from the types alone there's nothing preventing the "bytes_read * 8 * rng->quality" expression from mathematically exceeding INT_MAX and thus potentially becoming a negative value (so technically of course not greater than 0x7FFFFFFF, but the point being that the sign bit is set), and then the result of the division will most likely also be negative. But what actually saves the day is that I suppose bytes_read cannot be more than 32, so the multiplication is indeed at most 256*U16_MAX. Too bad we don't have a __postcond(@ret < (int)size) attribute we could put on functions like rng_get_data() to help static analysis. Rasmus
