From: Jason A. Donenfeld <Jason@zx2c4.com>
Date: Fri, 24 Dec 2021 18:17:58 +0000 (+0100)
Subject: random: do not sign extend bytes for rotation when mixing
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=08040365d0b7f69645d2f268ef8e428d3ab99187;p=linux.git

random: do not sign extend bytes for rotation when mixing

commit 0d9488ffbf2faddebc6bac055bfa6c93b94056a3 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/drivers/char/random.c b/drivers/char/random.c
index ca773f100fd60..8eac76539fddc 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -547,7 +547,7 @@ 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;