hashtable: fix environment variable corruption

Only first previously deleted entry was recognized, leading hsearch_r
to think that there was no previously deleted entry. It then conluded
that a free entry was found, even if there were no free entries and it
overwrote a random entry.

This patch makes sure all deleted or free entries are always found and
also introduces constants for the 0 and -1 numbers. Unit tests to excersise a
simple hash table usage and catch the corruption were added.

To trash your environment, simply run this loop:

setenv i 0
while true; do
    setenv v_$i $i
    setenv v_$i
    setexpr i $i + 1
done

Signed-off-by: Roman Kapl <rka@sysgo.com>

lib/hashtable.c

@@ -40,6 +40,9 @@
 #define	CONFIG_ENV_MAX_ENTRIES 512
 #endif
 
+#define USED_FREE 0
+#define USED_DELETED -1
+
 #include <env_callback.h>
 #include <env_flags.h>
 #include <search.h>
@@ -303,7 +306,7 @@ int hsearch_r(ENTRY item, ACTION action, ENTRY ** retval,
 		 */
 		unsigned hval2;
 
-		if (htab->table[idx].used == -1
+		if (htab->table[idx].used == USED_DELETED
 		    && !first_deleted)
 			first_deleted = idx;
 
@@ -335,13 +338,17 @@ int hsearch_r(ENTRY item, ACTION action, ENTRY ** retval,
 			if (idx == hval)
 				break;
 
+			if (htab->table[idx].used == USED_DELETED
+			    && !first_deleted)
+				first_deleted = idx;
+
 			/* If entry is found use it. */
 			ret = _compare_and_overwrite_entry(item, action, retval,
 				htab, flag, hval, idx);
 			if (ret != -1)
 				return ret;
 		}
-		while (htab->table[idx].used);
+		while (htab->table[idx].used != USED_FREE);
 	}
 
 	/* An empty bucket has been found. */
@@ -433,7 +440,7 @@ static void _hdelete(const char *key, struct hsearch_data *htab, ENTRY *ep,
 	free(ep->data);
 	ep->callback = NULL;
 	ep->flags = 0;
-	htab->table[idx].used = -1;
+	htab->table[idx].used = USED_DELETED;
 
 	--htab->filled;
 }

test/env/Makefile

@@ -4,3 +4,4 @@
 
 obj-y += cmd_ut_env.o
 obj-y += attr.o
+obj-y += hashtable.o

test/env/hashtable.c

@@ -0,0 +1,125 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * (C) Copyright 2019
+ * Roman Kapl, SYSGO, rka@sysgo.com
+ */
+
+#include <common.h>
+#include <command.h>
+#include <search.h>
+#include <stdio.h>
+#include <test/env.h>
+#include <test/ut.h>
+
+#define SIZE 32
+#define ITERATIONS 10000
+
+static int htab_fill(struct unit_test_state *uts,
+		     struct hsearch_data *htab, size_t size)
+{
+	size_t i;
+	ENTRY item;
+	ENTRY *ritem;
+	char key[20];
+
+	for (i = 0; i < size; i++) {
+		sprintf(key, "%d", (int)i);
+		item.callback = NULL;
+		item.data = key;
+		item.flags = 0;
+		item.key = key;
+		ut_asserteq(1, hsearch_r(item, ENTER, &ritem, htab, 0));
+	}
+
+	return 0;
+}
+
+static int htab_check_fill(struct unit_test_state *uts,
+			   struct hsearch_data *htab, size_t size)
+{
+	size_t i;
+	ENTRY item;
+	ENTRY *ritem;
+	char key[20];
+
+	for (i = 0; i < size; i++) {
+		sprintf(key, "%d", (int)i);
+		item.callback = NULL;
+		item.flags = 0;
+		item.data = key;
+		item.key = key;
+		hsearch_r(item, FIND, &ritem, htab, 0);
+		ut_assert(ritem);
+		ut_asserteq_str(key, ritem->key);
+		ut_asserteq_str(key, ritem->data);
+	}
+
+	return 0;
+}
+
+static int htab_create_delete(struct unit_test_state *uts,
+			      struct hsearch_data *htab, size_t iterations)
+{
+	size_t i;
+	ENTRY item;
+	ENTRY *ritem;
+	char key[20];
+
+	for (i = 0; i < iterations; i++) {
+		sprintf(key, "cd-%d", (int)i);
+		item.callback = NULL;
+		item.flags = 0;
+		item.data = key;
+		item.key = key;
+		hsearch_r(item, ENTER, &ritem, htab, 0);
+		ritem = NULL;
+
+		hsearch_r(item, FIND, &ritem, htab, 0);
+		ut_assert(ritem);
+		ut_asserteq_str(key, ritem->key);
+		ut_asserteq_str(key, ritem->data);
+
+		ut_asserteq(1, hdelete_r(key, htab, 0));
+	}
+
+	return 0;
+}
+
+/* Completely fill up the hash table */
+static int env_test_htab_fill(struct unit_test_state *uts)
+{
+	struct hsearch_data htab;
+
+	memset(&htab, 0, sizeof(htab));
+	ut_asserteq(1, hcreate_r(SIZE, &htab));
+
+	ut_assertok(htab_fill(uts, &htab, SIZE));
+	ut_assertok(htab_check_fill(uts, &htab, SIZE));
+	ut_asserteq(SIZE, htab.filled);
+
+	hdestroy_r(&htab);
+	return 0;
+}
+
+ENV_TEST(env_test_htab_fill, 0);
+
+/* Fill the hashtable up halfway an repeateadly delete/create elements
+ * and check for corruption
+ */
+static int env_test_htab_deletes(struct unit_test_state *uts)
+{
+	struct hsearch_data htab;
+
+	memset(&htab, 0, sizeof(htab));
+	ut_asserteq(1, hcreate_r(SIZE, &htab));
+
+	ut_assertok(htab_fill(uts, &htab, SIZE / 2));
+	ut_assertok(htab_create_delete(uts, &htab, ITERATIONS));
+	ut_assertok(htab_check_fill(uts, &htab, SIZE / 2));
+	ut_asserteq(SIZE / 2, htab.filled);
+
+	hdestroy_r(&htab);
+	return 0;
+}
+
+ENV_TEST(env_test_htab_deletes, 0);