Re: [PATCH 2/7] lib/mpi: use kcalloc in mpi_resize(Internet mail)

From: hongbo li <herbert.tencent@gmail.com>
To: Eric Biggers <ebiggers@kernel.org>
Cc: "herberthbli(李弘博)" <herberthbli@tencent.com>,
	"keyrings@vger.kernel.org" <keyrings@vger.kernel.org>,
	"linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
	"herbert@gondor.apana.org.au" <herbert@gondor.apana.org.au>,
	"dhowells@redhat.com" <dhowells@redhat.com>,
	"jarkko@kernel.org" <jarkko@kernel.org>,
	"tianjia.zhang@linux.alibaba.com"
	<tianjia.zhang@linux.alibaba.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/7] lib/mpi: use kcalloc in mpi_resize(Internet mail)
Date: Tue, 18 May 2021 21:53:04 +0800	[thread overview]
Message-ID: <CABpmuw+hs6__uWF=83psNRX-PbGuo+P8u3WXixswreBsqyne0Q@mail.gmail.com> (raw)
In-Reply-To: <YKLgIbI583asXCAc@gmail.com>

Ok， I'll explain it in the next version of patches.
Regards，
Hongbo

Eric Biggers <ebiggers@kernel.org> 于2021年5月18日周二 上午5:29写道：
>
> On Thu, May 13, 2021 at 02:49:03PM +0000, herberthbli(李弘博) wrote:
> > 在 2021/5/13 3:08, Eric Biggers 写道:
> >
> > On Wed, May 12, 2021 at 10:04:09PM +0800, Hongbo Li wrote:
> >
> >
> > From: Hongbo Li <herberthbli@tencent.com><mailto:herberthbli@tencent.com>
> >
> > 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@tencent.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 support.
> If that's indeed the case, what is the impact of that bug, and what commit is it
> fixing?  Please explain in the commit message and not just email.
>
> - Eric