random: do not sign extend bytes for rotation when mixing

By using `char` instead of `unsigned char`, certain platforms will sign
extend the byte when `w = rol32(*bytes++, input_rotate)` is called,
meaning that bit 7 is overrepresented when mixing. This isn't a real
problem (unless the mixer itself is already broken) since it's still
invertible, but it's not quite correct either. Fix this by using an
explicit unsigned type.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 99cce57..82db125 100644 (file)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -546,7 +546,7 @@ static void _mix_pool_bytes(struct entropy_store *r, const void *in,
        unsigned long i, tap1, tap2, tap3, tap4, tap5;
        int input_rotate;
        int wordmask = r->poolinfo->poolwords - 1;
-       const char *bytes = in;
+       const unsigned char *bytes = in;
        __u32 w;
 
        tap1 = r->poolinfo->tap1;