re: ACPICA: Resource Mgr: Prevent infinite loops in resource walks

[Dan Carpenter <dan.carpenter@oracle.com>]

Hello Bob Moore,

The patch c13085e519e8: "ACPICA: Resource Mgr: Prevent infinite loops 
in resource walks" from Mar 8, 2013 is not beautiful.  My static checker
complains about the loop because:
"drivers/acpi/acpica/rscalc.c:197 acpi_rs_get_aml_length()
	 warn: 'resource' can't be NULL."

drivers/acpi/acpica/rscalc.c
   195          /* Traverse entire list of internal resource descriptors */
   196  
   197          while (resource) {
                       ^^^^^^^^

My static checker is wrong because we use the -fno-strict-overflow to
prevent GCC from optimizing this check away.  But we are looping over
a list of pointers until our pointer wraps to NULL.  In other words we
loop over all the 2**64 - 1 addresses until we wrap to NULL or we find
something with an invalid type or something with ->length zero.

I assume the last element in the list always has length zero?  If so
then we could replace "while (resource)" with "while (resource->length)"

   198  
   199                  /* Validate the descriptor type */
   200  
   201                  if (resource->type > ACPI_RESOURCE_TYPE_MAX) {
   202                          return_ACPI_STATUS(AE_AML_INVALID_RESOURCE_TYPE);
   203                  }
   204  
   205                  /* Sanity check the length. It must not be zero, or we loop forever */
   206  
   207                  if (!resource->length) {
   208                          return_ACPI_STATUS(AE_AML_BAD_RESOURCE_LENGTH);
   209                  }
   210  
   211                  /* Get the base size of the (external stream) resource descriptor */
   212  

regards,
dan carpenter