mpi_copy: make the 0 case slightly more robust

If Y was constructed through functions in this module, then Y->n == 0
iff Y->p == NULL. However we do not prevent filling mpi structures
manually, and zero may be represented with n=0 and p a valid pointer.
Most of the code can cope with such a representation, but for the
source of mbedtls_mpi_copy, this would cause an integer underflow.
Changing the test for zero from Y->p==NULL to Y->n==0 causes this case
to work at no extra cost.

1 files changed, 1 insertions, 1 deletions

diff --git a/library/bignum.c b/library/bignum.c
index 6713bcbf..fdf571d2 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -198,7 +198,7 @@ int mbedtls_mpi_copy( mbedtls_mpi *X, const mbedtls_mpi *Y )
     if( X == Y )
         return( 0 );
 
-    if( Y->p == NULL )
+    if( Y->n == 0 )
     {
         mbedtls_mpi_free( X );
         return( 0 );