gpg: Graceful skip reading of corrupt MPIs.

* g10/parse-packet.c (mpi_read): Change error message on overflow.
--

This gets gpg 2.x in sync to what gpg 1.4 does.  No need to die for a
broken MPI.

GnuPG-bug-id: 1593

Resolved conflicts:
	g10/parse-packet.c - whitespaces fixes.

1 files changed, 18 insertions, 8 deletions

diff --git a/g10/parse-packet.c b/g10/parse-packet.c
index 424b052b9..26ca0381f 100644
--- a/g10/parse-packet.c
+++ b/g10/parse-packet.c
@@ -107,27 +107,32 @@ read_32 (IOBUF inp)
 static gcry_mpi_t
 mpi_read (iobuf_t inp, unsigned int *ret_nread, int secure)
 {
-  /*FIXME: Needs to be synced with gnupg14/mpi/mpicoder.c */
-
   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;
     }
-  nread = 2;
+
   nbytes = (nbits + 7) / 8;
   buf = secure ? gcry_xmalloc_secure (nbytes + 2) : gcry_xmalloc (nbytes + 2);
   p = buf;
@@ -136,18 +141,23 @@ mpi_read (iobuf_t inp, unsigned int *ret_nread, int secure)
   for (i = 0; i < nbytes; i++)
     {
       p[i + 2] = iobuf_get (inp) & 0xff;
+      if (nread == nmax)
+        goto overflow;
       nread++;
     }
 
   if (gcry_mpi_scan (&a, GCRYMPI_FMT_PGP, buf, nread, &nread))
     a = NULL;
 
+  *ret_nread = nread;
+  gcry_free(buf);
+  return a;
+
+ overflow:
+  log_error ("mpi larger than indicated length (%u bits)\n", 8*nmax);
  leave:
-  gcry_free (buf);
-  if (nread > *ret_nread)
-    log_bug ("mpi larger than packet (%zu/%u)", nread, *ret_nread);
-  else
-    *ret_nread = nread;
+  *ret_nread = nread;
+  gcry_free(buf);
   return a;
 }