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    Subject[PATCH 4.9 084/264] random: do not sign extend bytes for rotation when mixing
    Date
    From: "Jason A. Donenfeld" <Jason@zx2c4.com>

    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>
    ---
    drivers/char/random.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/drivers/char/random.c
    +++ b/drivers/char/random.c
    @@ -550,7 +550,7 @@ 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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