Add GCRYMPI_FLAG_IMMUTABLE to help debugging.

* src/gcrypt.h.in (GCRYMPI_FLAG_IMMUTABLE): New.
* src/mpi.h (mpi_is_immutable): New macro.
* mpi/mpiutil.c (gcry_mpi_set_flag, gcry_mpi_clear_flag)
(gcry_mpi_get_flag): Implement new flag
(_gcry_mpi_immutable_failed): New.

* mpi/mpiutil.c (_gcry_mpi_clear, _gcry_mpi_free, gcry_mpi_snatch)
(gcry_mpi_set, gcry_mpi_randomize): Act upon the immutable flag.
* mpi/mpi-bit.c (gcry_mpi_set_bit, gcry_mpi_set_highbit)
(gcry_mpi_clear_highbit, gcry_mpi_clear_bit)
(_gcry_mpi_rshift_limbs, gcry_mpi_lshift): Ditto.
* mpi/mpicoder.c (_gcry_mpi_set_buffer): Ditto.
--

Note that this flag is currently only checked by a few MPI functions.
The reason why we eventually need such a flag is to help implementing
a generic way to retrieve and set ECC parameters without accidentally
changing a curve parameter taken from a list of predefined curves.

1 files changed, 68 insertions, 25 deletions

diff --git a/mpi/mpi-bit.c b/mpi/mpi-bit.c
index cdc6b0b3..74042e89 100644
--- a/mpi/mpi-bit.c
+++ b/mpi/mpi-bit.c
@@ -1,5 +1,6 @@
 /* mpi-bit.c  -  MPI bit level functions
  * Copyright (C) 1998, 1999, 2001, 2002, 2006 Free Software Foundation, Inc.
+ * Copyright (C) 2013  g10 Code GmbH
  *
  * This file is part of Libgcrypt.
  *
@@ -117,6 +118,12 @@ gcry_mpi_set_bit( gcry_mpi_t a, unsigned int n )
 {
   unsigned int limbno, bitno;
 
+  if (mpi_is_immutable (a))
+    {
+      mpi_immutable_failed ();
+      return;
+    }
+
   limbno = n / BITS_PER_MPI_LIMB;
   bitno  = n % BITS_PER_MPI_LIMB;
 
@@ -136,6 +143,12 @@ gcry_mpi_set_highbit( gcry_mpi_t a, unsigned int n )
 {
   unsigned int limbno, bitno;
 
+  if (mpi_is_immutable (a))
+    {
+      mpi_immutable_failed ();
+      return;
+    }
+
   limbno = n / BITS_PER_MPI_LIMB;
   bitno  = n % BITS_PER_MPI_LIMB;
 
@@ -156,18 +169,23 @@ gcry_mpi_set_highbit( gcry_mpi_t a, unsigned int n )
 void
 gcry_mpi_clear_highbit( gcry_mpi_t a, unsigned int n )
 {
-    unsigned int limbno, bitno;
+  unsigned int limbno, bitno;
 
-    limbno = n / BITS_PER_MPI_LIMB;
-    bitno  = n % BITS_PER_MPI_LIMB;
+  if (mpi_is_immutable (a))
+    {
+      mpi_immutable_failed ();
+      return;
+    }
 
-    if( limbno >= a->nlimbs )
-	return; /* not allocated, therefore no need to clear bits
-		   :-) */
+  limbno = n / BITS_PER_MPI_LIMB;
+  bitno  = n % BITS_PER_MPI_LIMB;
+
+  if( limbno >= a->nlimbs )
+    return; /* not allocated, therefore no need to clear bits :-) */
 
-    for( ; bitno < BITS_PER_MPI_LIMB; bitno++ )
-	a->d[limbno] &= ~(A_LIMB_1 << bitno);
-    a->nlimbs = limbno+1;
+  for( ; bitno < BITS_PER_MPI_LIMB; bitno++ )
+    a->d[limbno] &= ~(A_LIMB_1 << bitno);
+  a->nlimbs = limbno+1;
 }
 
 /****************
@@ -176,14 +194,20 @@ gcry_mpi_clear_highbit( gcry_mpi_t a, unsigned int n )
 void
 gcry_mpi_clear_bit( gcry_mpi_t a, unsigned int n )
 {
-    unsigned int limbno, bitno;
+  unsigned int limbno, bitno;
 
-    limbno = n / BITS_PER_MPI_LIMB;
-    bitno  = n % BITS_PER_MPI_LIMB;
+  if (mpi_is_immutable (a))
+    {
+      mpi_immutable_failed ();
+      return;
+    }
 
-    if( limbno >= a->nlimbs )
-	return; /* don't need to clear this bit, it's to far to left */
-    a->d[limbno] &= ~(A_LIMB_1 << bitno);
+  limbno = n / BITS_PER_MPI_LIMB;
+  bitno  = n % BITS_PER_MPI_LIMB;
+
+  if (limbno >= a->nlimbs)
+    return; /* Don't need to clear this bit, it's far too left.  */
+  a->d[limbno] &= ~(A_LIMB_1 << bitno);
 }
 
 
@@ -194,19 +218,26 @@ gcry_mpi_clear_bit( gcry_mpi_t a, unsigned int n )
 void
 _gcry_mpi_rshift_limbs( gcry_mpi_t a, unsigned int count )
 {
-    mpi_ptr_t ap = a->d;
-    mpi_size_t n = a->nlimbs;
-    unsigned int i;
+  mpi_ptr_t ap = a->d;
+  mpi_size_t n = a->nlimbs;
+  unsigned int i;
 
-    if( count >= n ) {
-	a->nlimbs = 0;
-	return;
+  if (mpi_is_immutable (a))
+    {
+      mpi_immutable_failed ();
+      return;
     }
 
-    for( i = 0; i < n - count; i++ )
-	ap[i] = ap[i+count];
-    ap[i] = 0;
-    a->nlimbs -= count;
+  if (count >= n)
+    {
+      a->nlimbs = 0;
+      return;
+    }
+
+  for( i = 0; i < n - count; i++ )
+    ap[i] = ap[i+count];
+  ap[i] = 0;
+  a->nlimbs -= count;
 }
 
 
@@ -221,6 +252,12 @@ gcry_mpi_rshift ( gcry_mpi_t x, gcry_mpi_t a, unsigned int n )
   unsigned int nlimbs = (n/BITS_PER_MPI_LIMB);
   unsigned int nbits = (n%BITS_PER_MPI_LIMB);
 
+  if (mpi_is_immutable (x))
+    {
+      mpi_immutable_failed ();
+      return;
+    }
+
   if ( x == a )
     {
       /* In-place operation.  */
@@ -328,6 +365,12 @@ gcry_mpi_lshift ( gcry_mpi_t x, gcry_mpi_t a, unsigned int n )
   unsigned int nlimbs = (n/BITS_PER_MPI_LIMB);
   unsigned int nbits = (n%BITS_PER_MPI_LIMB);
 
+  if (mpi_is_immutable (x))
+    {
+      mpi_immutable_failed ();
+      return;
+    }
+
   if (x == a && !n)
     return;  /* In-place shift with an amount of zero.  */