Add accessor to get buf from mbedtls_pem_context

Co-authored-by: Gilles Peskine <gilles.peskine@arm.com>
Signed-off-by: Glenn Strauss <gstrauss@gluelogic.com>

ChangeLog.d/mbedtls_pem_get_der.txt

@@ -0,0 +1,2 @@
+Features
+   * Add accessor to get the raw buffer pointer from a PEM context.

include/mbedtls/pem.h

@@ -27,6 +27,11 @@
 
 #include <stddef.h>
 
+#if ( defined(__ARMCC_VERSION) || defined(_MSC_VER) ) && \
+    !defined(inline) && !defined(__cplusplus)
+#define inline __inline
+#endif
+
 /**
  * \name PEM Error codes
  * These error codes are returned in case of errors reading the
@@ -96,6 +101,10 @@ void mbedtls_pem_init( mbedtls_pem_context *ctx );
  *                  the decrypted text starts with an ASN.1 sequence of
  *                  appropriate length
  *
+ * \note            \c mbedtls_pem_free must be called on PEM context before
+ *                  the PEM context can be reused in another call to
+ *                  \c mbedtls_pem_read_buffer
+ *
  * \return          0 on success, or a specific PEM error code
  */
 int mbedtls_pem_read_buffer( mbedtls_pem_context *ctx, const char *header, const char *footer,
@@ -103,6 +112,25 @@ int mbedtls_pem_read_buffer( mbedtls_pem_context *ctx, const char *header, const
                      const unsigned char *pwd,
                      size_t pwdlen, size_t *use_len );
 
+/**
+ * \brief       Get the pointer to the decoded binary data in a PEM context.
+ *
+ * \param ctx       PEM context to access.
+ * \param buflen    On success, this will contain the length of the binary data.
+ *                  This must be a valid (non-null) pointer.
+ *
+ * \return          A pointer to the decoded binary data.
+ *
+ * \note            The returned pointer remains valid only until \p ctx is
+                    modified or freed.
+ */
+static inline const unsigned char *mbedtls_pem_get_buffer( mbedtls_pem_context *ctx, size_t *buflen )
+{
+    *buflen = ctx->MBEDTLS_PRIVATE(buflen);
+    return( ctx->MBEDTLS_PRIVATE(buf) );
+}
+
+
 /**
  * \brief       PEM context memory freeing
  *

tests/suites/test_suite_pem.function

@@ -40,12 +40,21 @@ void mbedtls_pem_read_buffer( char *header, char *footer, char *data,
     int ret;
     size_t use_len = 0;
     size_t pwd_len = strlen( pwd );
+    const unsigned char *buf;
 
     mbedtls_pem_init( &ctx );
 
     ret = mbedtls_pem_read_buffer( &ctx, header, footer, (unsigned char *)data,
                 (unsigned char *)pwd, pwd_len, &use_len );
     TEST_ASSERT( ret == res );
+    if( ret != 0 )
+        goto exit;
+
+    TEST_EQUAL( use_len, ctx.buflen );
+    use_len = 0;
+    buf = mbedtls_pem_get_buffer( &ctx, &use_len );
+    TEST_ASSERT( buf == ctx.buf );
+    TEST_EQUAL( use_len, ctx.buflen );
 
 exit:
     mbedtls_pem_free( &ctx );