Fix potential stack underflow in mpi_read_file.
When provided with an empty line, mpi_read_file causes a numeric
underflow resulting in a stack underflow. This commit fixes this and
adds some documentation to mpi_read_file.
diff --git a/include/mbedtls/bignum.h b/include/mbedtls/bignum.h
index aa51556..ffd308c 100644
--- a/include/mbedtls/bignum.h
+++ b/include/mbedtls/bignum.h
@@ -340,7 +340,7 @@
#if defined(MBEDTLS_FS_IO)
/**
- * \brief Read X from an opened file
+ * \brief Read MPI from a line in an opened file
*
* \param X Destination MPI
* \param radix Input numeric base
@@ -349,6 +349,15 @@
* \return 0 if successful, MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL if
* the file read buffer is too small or a
* MBEDTLS_ERR_MPI_XXX error code
+ *
+ * \note On success, this function advances the file stream
+ * to the end of the current line or to EOF.
+ *
+ * The function returns 0 on an empty line.
+ *
+ * Leading whitespaces are ignored, as is a
+ * '0x' prefix for radix 16.
+ *
*/
int mbedtls_mpi_read_file( mbedtls_mpi *X, int radix, FILE *fin );