hashmap: allow re-use after hashmap_free()

Previously, once map->table had been freed, any calls to hashmap_put(),
hashmap_get(), or hashmap_remove() would cause a NULL pointer
dereference (since hashmap_free_() also zeros the memory; without that
zeroing, calling these functions would cause a use-after-free problem).

Modify these functions to check for a NULL table and automatically
allocate as needed.

Also add a HASHMAP_INIT(fn, data) macro for initializing hashmaps on the
stack without calling hashmap_init().

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/hashmap.c b/hashmap.c
index e44d8a3e8598a33db0fa4baebb9e1fb1424d2f2f..bb7c9979b8d7e459439516237c747a08f000ace3 100644 (file)
--- a/hashmap.c
+++ b/hashmap.c
@@ -114,6 +114,7 @@ int hashmap_bucket(const struct hashmap *map, unsigned int hash)
 
 static void rehash(struct hashmap *map, unsigned int newsize)
 {
+       /* map->table MUST NOT be NULL when this function is called */
        unsigned int i, oldsize = map->tablesize;
        struct hashmap_entry **oldtable = map->table;
 
@@ -134,6 +135,7 @@ static void rehash(struct hashmap *map, unsigned int newsize)
 static inline struct hashmap_entry **find_entry_ptr(const struct hashmap *map,
                const struct hashmap_entry *key, const void *keydata)
 {
+       /* map->table MUST NOT be NULL when this function is called */
        struct hashmap_entry **e = &map->table[bucket(map, key)];
        while (*e && !entry_equals(map, *e, key, keydata))
                e = &(*e)->next;
@@ -196,6 +198,8 @@ struct hashmap_entry *hashmap_get(const struct hashmap *map,
                                const struct hashmap_entry *key,
                                const void *keydata)
 {
+       if (!map->table)
+               return NULL;
        return *find_entry_ptr(map, key, keydata);
 }
 
@@ -211,8 +215,12 @@ struct hashmap_entry *hashmap_get_next(const struct hashmap *map,
 
 void hashmap_add(struct hashmap *map, struct hashmap_entry *entry)
 {
-       unsigned int b = bucket(map, entry);
+       unsigned int b;
+
+       if (!map->table)
+               alloc_table(map, HASHMAP_INITIAL_SIZE);
 
+       b = bucket(map, entry);
        /* add entry */
        entry->next = map->table[b];
        map->table[b] = entry;
@@ -230,7 +238,11 @@ struct hashmap_entry *hashmap_remove(struct hashmap *map,
                                     const void *keydata)
 {
        struct hashmap_entry *old;
-       struct hashmap_entry **e = find_entry_ptr(map, key, keydata);
+       struct hashmap_entry **e;
+
+       if (!map->table)
+               return NULL;
+       e = find_entry_ptr(map, key, keydata);
        if (!*e)
                return NULL;
 

diff --git a/hashmap.h b/hashmap.h
index 904f61d6e15d0f957e370a6a31cd7aaae212b6aa..3b0f2bcadea118512afb64cba18d77f0a19fdeee 100644 (file)
--- a/hashmap.h
+++ b/hashmap.h
@@ -210,6 +210,9 @@ struct hashmap {
 
 /* hashmap functions */
 
+#define HASHMAP_INIT(fn, data) { .cmpfn = fn, .cmpfn_data = data, \
+                                .do_count_items = 1 }
+
 /*
  * Initializes a hashmap structure.
  *