commit 8d1dd1b5b9ffd1e615d1dea6524c8ea53a13216a
author Hanno Becker <hanno.becker@arm.com> Thu Sep 28 11:02:24 2017 +0100
committer Hanno Becker <hanno.becker@arm.com> Thu Sep 28 11:02:24 2017 +0100
tree 57b1c8efcb746abe1937d12a22aef7fe0c7078e7
parent a988a2702ab402e119502f9759347b12d91c0ee4

Fix bug in mbedtls_mpi_exp_mod

Calling `mbedtls_mpi_exp_mod` with a freshly initialized exponent MPI `N`,
i.e. `N.p == NULL`, would lead to a null-pointer dereference.

library/bignum.c

diff --git a/library/bignum.c b/library/bignum.c
index 8b9082c..e9ac565 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1614,7 +1614,7 @@
     mbedtls_mpi RR, T, W[ 2 << MBEDTLS_MPI_WINDOW_SIZE ], Apos;
     int neg;
 
-    if( mbedtls_mpi_cmp_int( N, 0 ) < 0 || ( N->p[0] & 1 ) == 0 )
+    if( mbedtls_mpi_cmp_int( N, 0 ) <= 0 || ( N->p[0] & 1 ) == 0 )
         return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
 
     if( mbedtls_mpi_cmp_int( E, 0 ) < 0 )