enforce a stack limit.

1 files changed, 13 insertions, 1 deletions

diff --git a/userprog/process.c b/userprog/process.c
index fdfb5dd..c13c051 100644
--- a/userprog/process.c
+++ b/userprog/process.c
@@ -595,7 +595,8 @@ setup_stack (uint32_t **esp, const char *args)
   const char *name = thread_current ()->name;
   char *argv_cur;
   uint32_t argc = 0;
-  unsigned namelen, argslen = strlen(args);
+  unsigned namelen, argslen = 0;
+  uint32_t *stack_end;
 
   kpage = palloc_get_page (PAL_USER | PAL_ZERO);
   if (kpage == NULL)
@@ -608,7 +609,14 @@ setup_stack (uint32_t **esp, const char *args)
 
   *esp = PHYS_BASE;
 
+  /* calculate end of stack which we'll enforce,
+     we need at least 4 entries for a correct stack and an
+     additional entry due to the way our argv[]-entries-loop works */
+  stack_end = PHYS_BASE - PGSIZE;
+  stack_end += 4 + 1;
+
   /* copy arguments to stack */
+  argslen = strlen(args);
   if (argslen > 0)
     {
       argslen += 1; /* add the trailing \0 */
@@ -651,6 +659,10 @@ setup_stack (uint32_t **esp, const char *args)
                   (*esp)--;
                   **esp = (uint32_t) argv_cur + 1;
                   argc++;
+
+                  /* check for possible stack overflow */
+                  if (*esp <= stack_end)
+                    return false;
                 }
             }
         }