Fix CVE-2020-12762.

This commit is a squashed and slightly modified backport
of the following commits on the master branch:

  * 77d935b
  * d07b910
  * 519dfe1
  * a59d5ac

linkhash.c

@@ -10,6 +10,7 @@
  *
  */
 
+#include <assert.h>
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
@@ -62,6 +63,8 @@ struct lh_table* lh_table_new(int size, const char *name,
 	int i;
 	struct lh_table *t;
 
+	/* Allocate space for elements to avoid divisions by zero. */
+	assert(size > 0);
 	t = (struct lh_table*)calloc(1, sizeof(struct lh_table));
 	if(!t) lh_abort("lh_table_new: calloc failed\n");
 	t->count = 0;
@@ -126,7 +129,14 @@ int lh_table_insert(struct lh_table *t, void *k, const void *v)
 	unsigned long h, n;
 
 	t->inserts++;
-	if(t->count >= t->size * LH_LOAD_FACTOR) lh_table_resize(t, t->size * 2);
+	if (t->count >= t->size * LH_LOAD_FACTOR) {
+		/* Avoid signed integer overflow with large tables. */
+		int new_size = (t->size > INT_MAX / 2) ? INT_MAX : (t->size * 2);
+		if (t->size == INT_MAX)
+			return -1;
+
+		lh_table_resize(t, new_size);
+	}
 
 	h = t->hash_fn(k);
 	n = h % t->size;

printbuf.c

@@ -15,6 +15,7 @@
 
 #include "config.h"
 
+#include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -63,7 +64,16 @@ static int printbuf_extend(struct printbuf *p, int min_size)
 	if (p->size >= min_size)
 		return 0;
 
-	new_size = json_max(p->size * 2, min_size + 8);
+	/* Prevent signed integer overflows with large buffers. */
+	if (min_size > INT_MAX - 8)
+		return -1;
+	if (p->size > INT_MAX / 2)
+		new_size =  min_size + 8;
+	else {
+		new_size = p->size * 2;
+		if (new_size < min_size + 8)
+			new_size = min_size + 8;
+	}
 #ifdef PRINTBUF_DEBUG
 	MC_DEBUG("printbuf_memappend: realloc "
 	  "bpos=%d min_size=%d old_size=%d new_size=%d\n",
@@ -78,6 +88,9 @@ static int printbuf_extend(struct printbuf *p, int min_size)
 
 int printbuf_memappend(struct printbuf *p, const char *buf, int size)
 {
+  /* Prevent signed integer overflows with large buffers. */
+  if (size > INT_MAX - p->bpos - 1)
+    return -1;
   if (p->size <= p->bpos + size + 1) {
     if (printbuf_extend(p, p->bpos + size + 1) < 0)
       return -1;
@@ -94,6 +107,9 @@ int printbuf_memset(struct printbuf *pb, int offset, int charvalue, int len)
 
 	if (offset == -1)
 		offset = pb->bpos;
+	/* Prevent signed integer overflows with large buffers. */
+	if (len > INT_MAX - offset)
+		return -1;
 	size_needed = offset + len;
 	if (pb->size < size_needed)
 	{

tests/test4.c

@@ -2,13 +2,17 @@
  * gcc -o utf8 utf8.c -I/home/y/include -L./.libs -ljson
 */
 
+#include "config.h"
+#include <assert.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
-#include "config.h"
 
 #include "json_inttypes.h"
 #include "json_object.h"
+#include "json_object_private.h"
 #include "json_tokener.h"
+#include "linkhash.h"
 
 void print_hex( const char* s) {
         const char *iter = s;
@@ -22,6 +26,28 @@ void print_hex( const char* s) {
         printf("\n");
 }
 
+static void test_lot_of_adds(void);
+static void test_lot_of_adds()
+{
+    int ii;
+    char key[50];
+    json_object *jobj = json_object_new_object();
+    assert(jobj != NULL);
+    for (ii = 0; ii < 500; ii++) {
+        snprintf(key, sizeof(key), "k%d", ii);
+        json_object *iobj = json_object_new_int(ii);
+        assert(iobj != NULL);
+        json_object_object_add(jobj, key, iobj);
+        if (json_object_object_get_ex(jobj, key, &iobj) == FALSE) {
+            fprintf(stderr, "FAILED to add object #%d\n", ii);
+            abort();
+        }
+    }
+    printf("%s\n", json_object_to_json_string(jobj));
+    assert(jobj->o.c_object->count == 500);
+    json_object_put(jobj);
+}
+
 int main() {
     const char *input = "\"\\ud840\\udd26,\\ud840\\udd27,\\ud800\\udd26,\\ud800\\udd27\"";
     const char *expected = "\xF0\xA0\x84\xA6,\xF0\xA0\x84\xA7,\xF0\x90\x84\xA6,\xF0\x90\x84\xA7";
@@ -45,5 +71,8 @@ int main() {
         retval = 1;
     }
 	json_object_put(parse_result);
+
+	test_lot_of_adds();
+
 	return retval;
 }