[PATCH 3/3] trans: remove the loop detection logic from the mtab translator

[Justus Winter]

Previously the mtab detector tried to detect whether it talks to
itself by comparing the control port of the translator it currently
visits with its own. This was done to prevent deadlocks. However, this
did not detect non-trivial loops, i.e. two mtab translators would
still dead-lock each other.

Now that it is safe to actually file_name_lookup the root node of a
mtab translator without triggering the generation of content, this
logic can just be omitted.

* trans/mtab.c (mtab_populate): Remove the loop detection logic.
---
 trans/mtab.c |   43 +++++++++++--------------------------------
 1 file changed, 11 insertions(+), 32 deletions(-)

diff --git a/trans/mtab.c b/trans/mtab.c
index b1a3939..d3c3583 100644
--- a/trans/mtab.c
+++ b/trans/mtab.c
@@ -286,7 +286,6 @@ mtab_populate (struct mtab *mtab, const char *path, int 
insecure)
 
   /* These resources are freed in the epilogue.         */
   file_t node = MACH_PORT_NULL;
-  fsys_t fsys = MACH_PORT_NULL;
   char *argz = NULL;
   size_t argz_len = 0;
   char **argv = NULL;
@@ -299,16 +298,16 @@ mtab_populate (struct mtab *mtab, const char *path, int 
insecure)
   char *children = NULL;
   size_t children_len = 0;
 
-  /* Get the underlying node.  */
-  node = file_name_lookup (path, O_NOTRANS, 0666);
-  if (node == MACH_PORT_NULL)
-    {
-      err = errno;
-      goto errout;
-    }
-
   if (! insecure)
     {
+      /* Get the underlying node.  */
+      node = file_name_lookup (path, O_NOTRANS, 0666);
+      if (node == MACH_PORT_NULL)
+        {
+          err = errno;
+          goto errout;
+        }
+
       /* Check who owns the node the translator is bound to.  */
       io_statbuf_t st;
       err = io_stat (node, &st);
@@ -320,28 +319,11 @@ mtab_populate (struct mtab *mtab, const char *path, int 
insecure)
          err = EPERM;
          goto errout;
        }
-    }
 
-  err = file_get_translator_cntl (node, &fsys);
-  if (err == EPERM)
-    /* If we do not have permission to do that, it cannot be a node
-       bound to our control port, so ignore this error.         */
-    err = 0;
-
-  if (err == ENXIO && strcmp (path, "/") == 0)
-    /* The root translator fails differently, but this can't be bound
-       to our control port either, so ignore this error.  */
-    err = 0;
-
-  if (err)
-    return err;
-
-  if (control && control->pi.port_right == fsys)
-    /* This node is bound to our control port, ignore it.  */
-    goto errout;
+      mach_port_deallocate (mach_task_self (), node);
+    }
 
-  /* Re-do the lookup without O_NOTRANS to get the root node.  */
-  mach_port_deallocate (mach_task_self (), node);
+  /* (Re-)do the lookup without O_NOTRANS to get the root node.  */
   node = file_name_lookup (path, 0, 0666);
   if (node == MACH_PORT_NULL)
     {
@@ -465,9 +447,6 @@ mtab_populate (struct mtab *mtab, const char *path, int 
insecure)
   if (node != MACH_PORT_NULL)
     mach_port_deallocate (mach_task_self (), node);
 
-  if (fsys != MACH_PORT_NULL)
-    mach_port_deallocate (mach_task_self (), fsys);
-
   if (argz)
     vm_deallocate (mach_task_self (), (vm_address_t) argz, argz_len);
 
-- 
1.7.10.4