On Mon, Apr 29, 2024 at 01:12:00AM +0300, Jarkko Sakkinen wrote:
> On Sat Apr 27, 2024 at 1:55 AM EEST, Stefan Berger wrote:
> > Protect ecc_digits_from_bytes from reading too many bytes from the input
> > byte array in case an insufficient number of bytes is provided to fill the
> > output digit array of ndigits. Therefore, initialize the most significant
> > digits with 0 to avoid trying to read too many bytes later on.
> >
> > If too many bytes are provided on the input byte array the extra bytes
> > are ignored since the input variable 'ndigits' limits the number of digits
> > that will be filled.
> >
> > Fixes: d67c96fb97b5 ("crypto: ecdsa - Convert byte arrays with key coordinates to digits")
> > Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
> > ---
> > include/crypto/internal/ecc.h | 7 +++++++
> > 1 file changed, 7 insertions(+)
> >
> > diff --git a/include/crypto/internal/ecc.h b/include/crypto/internal/ecc.h
> > index 7ca1f463d1ec..56215f14ff96 100644
> > --- a/include/crypto/internal/ecc.h
> > +++ b/include/crypto/internal/ecc.h
> > @@ -67,9 +67,16 @@ static inline void ecc_swap_digits(const void *in, u64 *out, unsigned int ndigit
> > static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
> > u64 *out, unsigned int ndigits)
> > {
> > + int diff = ndigits - DIV_ROUND_UP(nbytes, sizeof(u64));
> > unsigned int o = nbytes & 7;
> > __be64 msd = 0;
> >
> > + /* diff > 0: not enough input bytes: set most significant digits to 0 */
> > + while (diff > 0) {
> > + out[--ndigits] = 0;
> > + diff--;
> > + }
>
> Could be just trivial for-loop:
>
> for (i = 0; i < diff; i++)
> out[--ndigits] = 0;
>
> Or also simpler while-loop could work:
>
> while (diff-- > 0)
> out[--ndigits] = 0;
Or just use memset(), which uses optimized instructions on many arches.
