Messages in this thread | | | Date | Mon, 29 Apr 2024 07:11:45 -0400 | Subject | Re: [PATCH] crypto: ecc - Protect ecc_digits_from_bytes from reading too many bytes | From | Stefan Berger <> |
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On 4/29/24 06:14, Jarkko Sakkinen wrote: > On Mon Apr 29, 2024 at 6:30 AM EEST, Lukas Wunner wrote: >> 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@linux.ibm.com> >>>> --- >>>> 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. > > Yeah, sure, that would be even better, or even memzero_explicit()?
Thanks. The function isn't getting too big for an inline?
> > BR, Jarkko
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