Re: [PATCH v2] crypto: ecc - Prevent ecc_digits_from_bytes from reading too many bytes

[Jarkko Sakkinen]

On Mon Apr 29, 2024 at 7:57 PM EEST, Stefan Berger wrote:
>
>
> On 4/29/24 12:47, Jarkko Sakkinen wrote:
> > On Mon Apr 29, 2024 at 7:13 PM EEST, Stefan Berger wrote:
> >> Prevent 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. Convert the
> >> function into a regular function since it is getting too big for an inline
> >> function.
> >>
> >> 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>
> >>
> >> ---
> >>
> >> v2:
> >>   - un-inline function
> >>   - use memset
> >> ---
> >>   crypto/ecc.c                  | 22 ++++++++++++++++++++++
> >>   include/crypto/internal/ecc.h | 15 ++-------------
> >>   2 files changed, 24 insertions(+), 13 deletions(-)
> >>
> >> diff --git a/crypto/ecc.c b/crypto/ecc.c
> >> index c1d2e884be1e..fe761256e335 100644
> >> --- a/crypto/ecc.c
> >> +++ b/crypto/ecc.c
> >> @@ -68,6 +68,28 @@ const struct ecc_curve *ecc_get_curve(unsigned int curve_id)
> >>   }
> >>   EXPORT_SYMBOL(ecc_get_curve);
> >>   
> > 
> > Just a minor nit:
> > 
> > For exported symbol you need to document the function,including
> > the parameters [1].
>
> Like other functions, the ecc_digits_from_bytes also still/already has 
> the documentation in the header file:
>
> /**
>   * ecc_digits_from_bytes() - Create ndigits-sized digits array from 
> byte array
>   * @in:       Input byte array
>   * @nbytes    Size of input byte array
>   * @out       Output digits array
>   * @ndigits:  Number of digits to create from byte array
>   */
> void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
>                             u64 *out, unsigned int ndigits);
>
>   Should be ok?

I think it should be OK, or at least documentation has not denied
doing that and gives example how to import from header files:

https://www.kernel.org/doc/html/latest/doc-guide/kernel-doc.html

Just had not encountered that before so that said

Reviewed-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>

BR, Jarkko