commit c9529f96498e863ab449b37f8da9b6d661bd0367
author Gilles Peskine <Gilles.Peskine@arm.com> Thu Jun 09 19:32:46 2022 +0200
committer Gilles Peskine <Gilles.Peskine@arm.com> Mon Jun 27 14:48:44 2022 +0200
tree a15e4059b14cdc5626623f29e218daa2756d2819
parent 8776042e44bcc2cf8a6ccddb031dfcdb03f26865

Fix null pointer dereference in mpi_mod_int(0, 2)

Fix a null pointer dereference when performing some operations on zero
represented with 0 limbs: mbedtls_mpi_mod_int() dividing by 2, or
mbedtls_mpi_write_string() in base 2.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

library/bignum.c

diff --git a/library/bignum.c b/library/bignum.c
index db29ae5..32578e2 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1829,7 +1829,7 @@
     /*
      * handle trivial cases
      */
-    if( b == 1 )
+    if( b == 1 || A->n == 0 )
     {
         *r = 0;
         return( 0 );