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Subject[PATCH 4.19 051/234] random: do not sign extend bytes for rotation when mixing
From: "Jason A. Donenfeld" <>

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 <>
Signed-off-by: Greg Kroah-Hartman <>
drivers/char/random.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -549,7 +549,7 @@ static void _mix_pool_bytes(struct entro
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;

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