gpg: Accept Ed25519 private key in SOS which reserves leading zeros.

* g10/parse-packet.c (sos_read): Backport from 2.3.
(parse_key): Use sos_read for Ed25519 private key.

--

Note that we keep the code of sos_read as same as 2.3.  Even it is
set, the GCRYMPI_FLAG_USER2 flag is not used.

GnuPG-bug-id: 5120
Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>

g10/parse-packet.c

@@ -188,6 +188,76 @@ mpi_read (iobuf_t inp, unsigned int *ret_nread, int secure)
 }
 
 
+/* Read an external representation of an SOS and return the opaque MPI
+   with GCRYMPI_FLAG_USER2.  The external format is a 16-bit unsigned
+   value stored in network byte order giving information for the
+   following octets.
+
+   The caller must set *RET_NREAD to the maximum number of bytes to
+   read from the pipeline INP.  This function sets *RET_NREAD to be
+   the number of bytes actually read from the pipeline.
+
+   If SECURE is true, the integer is stored in secure memory
+   (allocated using gcry_xmalloc_secure).  */
+static gcry_mpi_t
+sos_read (iobuf_t inp, unsigned int *ret_nread, int secure)
+{
+  int c, c1, c2, i;
+  unsigned int nmax = *ret_nread;
+  unsigned int nbits, nbytes;
+  size_t nread = 0;
+  gcry_mpi_t a = NULL;
+  byte *buf = NULL;
+  byte *p;
+
+  if (!nmax)
+    goto overflow;
+
+  if ((c = c1 = iobuf_get (inp)) == -1)
+    goto leave;
+  if (++nread == nmax)
+    goto overflow;
+  nbits = c << 8;
+  if ((c = c2 = iobuf_get (inp)) == -1)
+    goto leave;
+  ++nread;
+  nbits |= c;
+  if (nbits > MAX_EXTERN_MPI_BITS)
+    {
+      log_error ("mpi too large (%u bits)\n", nbits);
+      goto leave;
+    }
+
+  nbytes = (nbits + 7) / 8;
+  buf = secure ? gcry_xmalloc_secure (nbytes) : gcry_xmalloc (nbytes);
+  p = buf;
+  for (i = 0; i < nbytes; i++)
+    {
+      if (nread == nmax)
+        goto overflow;
+
+      c = iobuf_get (inp);
+      if (c == -1)
+        goto leave;
+
+      p[i] = c;
+      nread ++;
+    }
+
+  a = gcry_mpi_set_opaque (NULL, buf, nbits);
+  gcry_mpi_set_flag (a, GCRYMPI_FLAG_USER2);
+  *ret_nread = nread;
+  return a;
+
+ overflow:
+  log_error ("mpi larger than indicated length (%u bits)\n", 8*nmax);
+ leave:
+  *ret_nread = nread;
+  gcry_free(buf);
+  return a;
+}
+
+
 /* Register STRING as a known critical notation name.  */
 void
 register_known_notation (const char *string)
@@ -2728,6 +2798,9 @@ parse_key (IOBUF inp, int pkttype, unsigned long pktlen,
                   goto leave;
                 }
               n = pktlen;
+              if (algorithm == PUBKEY_ALGO_EDDSA)
+                pk->pkey[i] = sos_read (inp, &n, 0);
+              else
                 pk->pkey[i] = mpi_read (inp, &n, 0);
               pktlen -= n;
               if (list_mode)