Track where microdescs are referenced to prevent free errs

On IRC, wanoskarnet notes that if we ever do microdesc_free() on a
microdesc that's in the nodelist, we're in trouble.  Also, we're in
trouble if we free one that's still in the microdesc_cache map.

This code adds a flag to microdesc_t to note where the microdesc is
referenced from, and checks those flags from microdesc_free().  I
don't believe we have any errors here now, but if we introduce some
later, let's log and recover from them rather than introducing
heisenbugs later on.

Addresses bug 3153.

1 files changed, 5 insertions, 0 deletions

diff --git a/src/or/or.h b/src/or/or.h
index f58876e496..ddc03be87c 100644
--- a/src/or/or.h
+++ b/src/or/or.h
@@ -1709,6 +1709,11 @@ typedef struct microdesc_t {
   saved_location_t saved_location : 3;
   /** If true, do not attempt to cache this microdescriptor on disk. */
   unsigned int no_save : 1;
+  /** If true, this microdesc is attached to a node_t. */
+  unsigned int held_by_node : 1;
+  /** If true, this microdesc has an entry in the microdesc_map */
+  unsigned int held_in_map : 1;
+
   /** If saved_location == SAVED_IN_CACHE, this field holds the offset of the
    * microdescriptor in the cache. */
   off_t off;