libctf: don't leak hash keys or values on value replacement

When a ctf_dynhash_insert() finds a slot already existing, it should
call the key and value free functions on the existing key and value and
move the passed-in key into place, so that the lifetime rules for hash
keys are always the same no matter whether the key existed or not but
neither are the keys or values leaked.

New in v3.
v5: fix tabdamage.

libctf/
	* ctf-hash.c (ctf_hashtab_insert): Pass in the key and value
	freeing functions: if set, free the key and value if the slot
	already exists.  Always reassign the key.
	(ctf_dynhash_insert): Adjust call appropriately.
	(ctf_hash_insert_type): Likewise.

2 files changed, 22 insertions, 4 deletions

diff --git a/libctf/ChangeLog b/libctf/ChangeLog
index 28be757..08a2e3a 100644
--- a/libctf/ChangeLog
+++ b/libctf/ChangeLog
@@ -1,3 +1,11 @@
+2019-07-30  Nick Alcock  <nick.alcock@oracle.com>
+
+	* ctf-hash.c (ctf_hashtab_insert): Pass in the key and value
+	freeing functions: if set, free the key and value if the slot
+	already exists.  Always reassign the key.
+	(ctf_dynhash_insert): Adjust call appropriately.
+	(ctf_hash_insert_type): Likewise.
+
 2019-08-03  Nick Alcock  <nick.alcock@oracle.com>
 
 	* ctf-create.c (ctf_add_type): Look up and use the forwarded-to
diff --git a/libctf/ctf-hash.c b/libctf/ctf-hash.c
index c6233eb..59fceed 100644
--- a/libctf/ctf-hash.c
+++ b/libctf/ctf-hash.c
@@ -152,7 +152,9 @@ ctf_hashtab_lookup (struct htab *htab, const void *key, enum insert_option inser
 }
 
 static ctf_helem_t *
-ctf_hashtab_insert (struct htab *htab, void *key, void *value)
+ctf_hashtab_insert (struct htab *htab, void *key, void *value,
+		    ctf_hash_free_fun key_free,
+		    ctf_hash_free_fun value_free)
 {
   ctf_helem_t **slot;
 
@@ -169,8 +171,15 @@ ctf_hashtab_insert (struct htab *htab, void *key, void *value)
       *slot = malloc (sizeof (ctf_helem_t));
       if (!*slot)
 	return NULL;
-      (*slot)->key = key;
     }
+  else
+    {
+      if (key_free)
+	  key_free ((*slot)->key);
+      if (value_free)
+	  value_free ((*slot)->value);
+    }
+  (*slot)->key = key;
   (*slot)->value = value;
   return *slot;
 }
@@ -180,7 +189,8 @@ ctf_dynhash_insert (ctf_dynhash_t *hp, void *key, void *value)
 {
   ctf_helem_t *slot;
 
-  slot = ctf_hashtab_insert (hp->htab, key, value);
+  slot = ctf_hashtab_insert (hp->htab, key, value,
+			     hp->key_free, hp->value_free);
 
   if (!slot)
     return errno;
@@ -317,7 +327,7 @@ ctf_hash_insert_type (ctf_hash_t *hp, ctf_file_t *fp, uint32_t type,
     return 0;		   /* Just ignore empty strings on behalf of caller.  */
 
   if (ctf_hashtab_insert ((struct htab *) hp, (char *) str,
-			  (void *) (ptrdiff_t) type) != NULL)
+			  (void *) (ptrdiff_t) type, NULL, NULL) != NULL)
     return 0;
   return errno;
 }