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From:   hongbo li <herbert.tencent@gmail.com>
Date:   Tue, 18 May 2021 21:53:04 +0800
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Subject: Re: [PATCH 2/7] lib/mpi: use kcalloc in mpi_resize(Internet mail)
To:     Eric Biggers <ebiggers@kernel.org>
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Ok=EF=BC=8C I'll explain it in the next version of patches.
Regards=EF=BC=8C
Hongbo

Eric Biggers <ebiggers@kernel.org> =E4=BA=8E2021=E5=B9=B45=E6=9C=8818=E6=97=
=A5=E5=91=A8=E4=BA=8C =E4=B8=8A=E5=8D=885:29=E5=86=99=E9=81=93=EF=BC=9A
>
> On Thu, May 13, 2021 at 02:49:03PM +0000, herberthbli(=E6=9D=8E=E5=BC=98=
=E5=8D=9A) wrote:
> > =E5=9C=A8 2021/5/13 3:08, Eric Biggers =E5=86=99=E9=81=93:
> >
> > On Wed, May 12, 2021 at 10:04:09PM +0800, Hongbo Li wrote:
> >
> >
> > From: Hongbo Li <herberthbli@tencent.com><mailto:herberthbli@tencent.co=
m>
> >
> > We should set the additional space to 0 in mpi_resize().
> > So use kcalloc() instead of kmalloc_array().
> >
> > Signed-off-by: Hongbo Li <herberthbli@tencent.com><mailto:herberthbli@t=
encent.com>
> >
> >
> >
> > Is this fixing something, and if so what?
> >
> > - Eric
> >
> >
> >
> > In lib/mpi/ec.c:
> >
> > /****************
> >  * Resize the array of A to NLIMBS. the additional space is cleared
> >  * (set to 0) [done by m_realloc()]
> >  */
> > int mpi_resize(MPI a, unsigned nlimbs)
> >
> > Like the comment of kernel's mpi_resize(), the additional space need to=
 set to 0,
> > but when a->d is not NULL, it does not set.
> >
> > The kernel's mpi lib is from libgcrypt, the mpi resize in libgcrypt is =
_gcry_mpi_resize()
> > which set the additional space to 0.
> >
> > This issue will cause add_points_edwards() get a wrong result, and lead=
 to a failed
> > eddsa verification.
> >
>
> That sounds like it's fixing an existing bug, regardless of the ed25519 s=
upport.
> If that's indeed the case, what is the impact of that bug, and what commi=
t is it
> fixing?  Please explain in the commit message and not just email.
>
> - Eric