[PATCH] potential memory corruption in calls to gnutls function on 64 bit arch

Looking at lockdown.c:

   / if everything went well, export in PEM format /
   gnutls_datum_t dev_pem = { NULL, 0 };
   gnutls_x509_crt_export(dev_cert, GNUTLS_X509_FMT_PEM, NULL, &dev_pem.size);
   dev_pem.data = gnutls_malloc(dev_pem.size);
   gnutls_x509_crt_export(dev_cert, GNUTLS_X509_FMT_PEM, dev_pem.data, &dev_pem.size);

On my box, gnutls_datum_t is:

   typedef struct
   {

   unsigned char *data;
   unsigned int size;

   } gnutls_datum_t;

and gnutls_x509_crt_export has this prototype:

   int gnutls_x509_crt_export(gnutls_x509_crt_t cert,

                          gnutls_x509_crt_fmt_t format,
                          void  *output_data,
                          size_t *output_data_size);</code>

ints are 4 bytes long on x86_64/linux, size_t is 8 bytes long, so when passing &dev_pem.size to gnutls_x509_crt_export, the 4 bytes after &dev_pem.size might be written to. In this case, these 4 bytes are padding in the gnutls_datum_t, but I wouldn't rely on that.

The same issue is present in userpref.c. gcc complains about it when compiling with -Wall -Werror.