Bugfix/MICRSE-4914: Fix incorrect memory freeing in build_pkcs11_uri()

- Use a const pointer to prevent modification of memory returned by getenv().
- Free env_result before reassigning it to prevent invalid memory operations and memory leaks.

Issue originally reported in PR #11.

Reported-by: @andersm
Signed-off-by: Mario Castaneda <mario.ignacio.castaneda.lopez@nxp.com>

Author: marioicastal

inc/imx_signer.h

@@ -196,8 +196,8 @@ typedef struct {
 static bool g_debug = 0;
 static char *g_cfgfilename = NULL;
 extern uint32_t g_image_offset;
-static char *g_sig_tool_path = NULL;
-static char *g_sig_data_path = NULL;
+static const char *g_sig_tool_path = NULL;
+static const char *g_sig_data_path = NULL;
 
 unsigned char g_ivt_v1_mask[] = {0xFF,0xFF,0xFF,0xF0};
 unsigned char g_ivt_v1[] = {0xD1,0x00,0x20,0x41};

src/imx_signer.c

@@ -564,7 +564,7 @@ static char *build_pkcs11_uri(const char *rvalue) {
     char *pkcs11_uri = NULL;        /* PKCS11 URI string buffer */
     char *env_result = NULL;        /* Env result for Token*/
     char *config_object = NULL;     /* Configuration object identifier */
-    char *pkcs11_token_pin = NULL;  /* Token or Pin values*/
+    const char *pkcs11_token_pin = NULL;  /* Token or Pin values*/
 
     /* Allocate buffer for the complete PKCS11 URI */
     pkcs11_uri = calloc(PKCS11_URI_BUFFER_SIZE+1, sizeof(char));
@@ -604,7 +604,7 @@ static char *build_pkcs11_uri(const char *rvalue) {
         goto err;
 
     pkcs11_token_pin = NULL;
-    env_result = NULL;
+    FREE(env_result);
 
     /* Add type=cert */
     strncat(pkcs11_uri, ";type=cert", PKCS11_URI_BUFFER_SIZE - strlen(pkcs11_uri));
@@ -619,22 +619,17 @@ static char *build_pkcs11_uri(const char *rvalue) {
             strncat(pkcs11_uri, pkcs11_token_pin, PKCS11_URI_BUFFER_SIZE - strlen(pkcs11_uri));
         else
             strncat(pkcs11_uri, env_result, PKCS11_URI_BUFFER_SIZE - strlen(pkcs11_uri));
-        FREE(env_result);
     } else
         goto err;
 
     /* Close the URI string */
     strncat(pkcs11_uri, "\"", PKCS11_URI_BUFFER_SIZE - strlen(pkcs11_uri));
 
-    FREE(pkcs11_token_pin);
     FREE(config_object);
     FREE(env_result);
-    FREE(pkcs11_uri);
-
     return pkcs11_uri;
 
 err:
-    FREE(pkcs11_token_pin);
     FREE(config_object);
     FREE(env_result);
     FREE(pkcs11_uri);