libgcrypt: solve CVE-2021-33560 and CVE-2021-40528

This change fixes patches for two issues reported in a research
paper [1]: a side channel attack (*) and a cross-configuration
attack (**).

In this commit we add a fix for (*) that wasn't marked as a CVE
initially in the upstream. A fix of (**) available in Yocto
backport is in fact fixing CVE-2021-40528, not CVE-2021-33560
as marked in the commit message.

We commit the accual fix for CVE-2021-33560 and whitelist
CVE-2021-40528 until we rename the patch upstream.

For details of the mismatch and the timeline see [2] (fix of the
documentation) and [3] (the related ticket upstream).

[1] https://eprint.iacr.org/2021/923.pdf
[2] https://dev.gnupg.org/rCb118681ebc4c9ea4b9da79b0f9541405a64f4c13
[3] https://dev.gnupg.org/T5328#149606



Signed-off-by: Marta Rybczynska <marta.rybczynska@huawei.com>

meta-oniro-staging/recipes-support/libgcrypt/files/CVE-2021-33560_2.patch

+From e8b7f10be275bcedb5fc05ed4837a89bfd605c61 Mon Sep 17 00:00:00 2001
+From: NIIBE Yutaka <gniibe@fsij.org>
+Date: Tue, 13 Apr 2021 10:00:00 +0900
+Subject: [PATCH] cipher: Hardening ElGamal by introducing exponent blinding
+ too.
+
+* cipher/elgamal.c (do_encrypt): Also do exponent blinding.
+
+--
+
+Base blinding had been introduced with USE_BLINDING.  This patch add
+exponent blinding as well to mitigate side-channel attack on mpi_powm.
+
+GnuPG-bug-id: 5328
+Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>
+
+Upstream-Status: Backport [https://git.gnupg.org/cgi-bin/gitweb.cgi?p=libgcrypt.git;a=commit;h=e8b7f10be275bcedb5fc05ed4837a89bfd605c61]
+CVE: CVE-2021-33560
+Signed-off-by: Marta Rybczynska <marta.rybczynska@huawei.com>
+---
+ cipher/elgamal.c | 20 +++++++++++++++++---
+ 1 file changed, 17 insertions(+), 3 deletions(-)
+
+diff --git a/cipher/elgamal.c b/cipher/elgamal.c
+index 4eb52d62..9835122f 100644
+--- a/cipher/elgamal.c
++++ b/cipher/elgamal.c
+@@ -522,8 +522,9 @@ do_encrypt(gcry_mpi_t a, gcry_mpi_t b, gcry_mpi_t input, ELG_public_key *pkey )
+ static void
+ decrypt (gcry_mpi_t output, gcry_mpi_t a, gcry_mpi_t b, ELG_secret_key *skey )
+ {
+-  gcry_mpi_t t1, t2, r;
++  gcry_mpi_t t1, t2, r, r1, h;
+   unsigned int nbits = mpi_get_nbits (skey->p);
++  gcry_mpi_t x_blind;
+ 
+   mpi_normalize (a);
+   mpi_normalize (b);
+@@ -534,20 +535,33 @@ decrypt (gcry_mpi_t output, gcry_mpi_t a, gcry_mpi_t b, ELG_secret_key *skey )
+ 
+   t2 = mpi_snew (nbits);
+   r  = mpi_new (nbits);
++  r1 = mpi_new (nbits);
++  h  = mpi_new (nbits);
++  x_blind = mpi_snew (nbits);
+ 
+   /* We need a random number of about the prime size.  The random
+      number merely needs to be unpredictable; thus we use level 0.  */
+   _gcry_mpi_randomize (r, nbits, GCRY_WEAK_RANDOM);
+ 
++  /* Also, exponent blinding: x_blind = x + (p-1)*r1 */
++  _gcry_mpi_randomize (r1, nbits, GCRY_WEAK_RANDOM);
++  mpi_set_highbit (r1, nbits - 1);
++  mpi_sub_ui (h, skey->p, 1);
++  mpi_mul (x_blind, h, r1);
++  mpi_add (x_blind, skey->x, x_blind);
++
+   /* t1 = r^x mod p */
+-  mpi_powm (t1, r, skey->x, skey->p);
++  mpi_powm (t1, r, x_blind, skey->p);
+   /* t2 = (a * r)^-x mod p */
+   mpi_mulm (t2, a, r, skey->p);
+-  mpi_powm (t2, t2, skey->x, skey->p);
++  mpi_powm (t2, t2, x_blind, skey->p);
+   mpi_invm (t2, t2, skey->p);
+   /* t1 = (t1 * t2) mod p*/
+   mpi_mulm (t1, t1, t2, skey->p);
+ 
++  mpi_free (x_blind);
++  mpi_free (h);
++  mpi_free (r1);
+   mpi_free (r);
+   mpi_free (t2);
+ 
+-- 
+2.11.0
+

meta-oniro-staging/recipes-support/libgcrypt/libgcrypt_1.8.5.bbappend

+# SPDX-FileCopyrightText: Huawei Inc.
+#
+# SPDX-License-Identifier: Apache-2.0
+
+FILESEXTRAPATHS_prepend := "${THISDIR}/files:"
+
+SRC_URI += "file://CVE-2021-33560_2.patch"
+
+# A fix marked as a fix for CVE-2021-33560 in dunfell is in fact
+# fixing CVE-2021-40528. Mark it as whitelisted until solved properly
+# (renaming the fix in the upstream)
+# For the mismatch between CVE-2021-33560 and CVE-2021-40528 see
+# https://dev.gnupg.org/T5328
+CVE_CHECK_WHITELIST += "CVE-2021-40528"