Fix integer overflow (CVE-2021-21309). (#8522)

On 32-bit systems, setting the proto-max-bulk-len config parameter to a high value may result with integer overflow and a subsequent heap overflow when parsing an input bulk (CVE-2021-21309).

This fix has two parts:

Set a reasonable limit to the config parameter.
Add additional checks to prevent the problem in other potential but unknown code paths.

src/config.c

@@ -2517,7 +2517,7 @@ standardConfig configs[] = {
     createLongLongConfig("cluster-node-timeout", NULL, MODIFIABLE_CONFIG, 0, LLONG_MAX, server.cluster_node_timeout, 15000, INTEGER_CONFIG, NULL, NULL),
     createLongLongConfig("slowlog-log-slower-than", NULL, MODIFIABLE_CONFIG, -1, LLONG_MAX, server.slowlog_log_slower_than, 10000, INTEGER_CONFIG, NULL, NULL),
     createLongLongConfig("latency-monitor-threshold", NULL, MODIFIABLE_CONFIG, 0, LLONG_MAX, server.latency_monitor_threshold, 0, INTEGER_CONFIG, NULL, NULL),
-    createLongLongConfig("proto-max-bulk-len", NULL, MODIFIABLE_CONFIG, 1024*1024, LLONG_MAX, server.proto_max_bulk_len, 512ll*1024*1024, MEMORY_CONFIG, NULL, NULL), /* Bulk request max size */
+    createLongLongConfig("proto-max-bulk-len", NULL, MODIFIABLE_CONFIG, 1024*1024, LONG_MAX, server.proto_max_bulk_len, 512ll*1024*1024, MEMORY_CONFIG, NULL, NULL), /* Bulk request max size */
     createLongLongConfig("stream-node-max-entries", NULL, MODIFIABLE_CONFIG, 0, LLONG_MAX, server.stream_node_max_entries, 100, INTEGER_CONFIG, NULL, NULL),
     createLongLongConfig("repl-backlog-size", NULL, MODIFIABLE_CONFIG, 1, LLONG_MAX, server.repl_backlog_size, 1024*1024, MEMORY_CONFIG, NULL, updateReplBacklogSize), /* Default: 1mb */
 

src/sds.c

@@ -111,6 +111,7 @@ sds _sdsnewlen(const void *init, size_t initlen, int trymalloc) {
     unsigned char *fp; /* flags pointer. */
     size_t usable;
 
+    assert(initlen + hdrlen + 1 > initlen); /* Catch size_t overflow */
     sh = trymalloc?
         s_trymalloc_usable(hdrlen+initlen+1, &usable) :
         s_malloc_usable(hdrlen+initlen+1, &usable);
@@ -243,6 +244,7 @@ sds sdsMakeRoomFor(sds s, size_t addlen) {
     len = sdslen(s);
     sh = (char*)s-sdsHdrSize(oldtype);
     newlen = (len+addlen);
+    assert(newlen > len);   /* Catch size_t overflow */
     if (newlen < SDS_MAX_PREALLOC)
         newlen *= 2;
     else
@@ -256,6 +258,7 @@ sds sdsMakeRoomFor(sds s, size_t addlen) {
     if (type == SDS_TYPE_5) type = SDS_TYPE_8;
 
     hdrlen = sdsHdrSize(type);
+    assert(hdrlen + newlen + 1 > len);  /* Catch size_t overflow */
     if (oldtype==type) {
         newsh = s_realloc_usable(sh, hdrlen+newlen+1, &usable);
         if (newsh == NULL) return NULL;

src/zmalloc.c

@@ -57,6 +57,12 @@ void zlibc_free(void *ptr) {
 #endif
 #endif
 
+#if PREFIX_SIZE > 0
+#define ASSERT_NO_SIZE_OVERFLOW(sz) assert((sz) + PREFIX_SIZE > (sz))
+#else
+#define ASSERT_NO_SIZE_OVERFLOW(sz)
+#endif
+
 /* Explicitly override malloc/free etc when using tcmalloc. */
 #if defined(USE_TCMALLOC)
 #define malloc(size) tc_malloc(size)
@@ -89,6 +95,7 @@ static void (*zmalloc_oom_handler)(size_t) = zmalloc_default_oom;
 /* Try allocating memory, and return NULL if failed.
  * '*usable' is set to the usable size if non NULL. */
 void *ztrymalloc_usable(size_t size, size_t *usable) {
+    ASSERT_NO_SIZE_OVERFLOW(size);
     void *ptr = malloc(size+PREFIX_SIZE);
 
     if (!ptr) return NULL;
@@ -131,6 +138,7 @@ void *zmalloc_usable(size_t size, size_t *usable) {
  * Currently implemented only for jemalloc. Used for online defragmentation. */
 #ifdef HAVE_DEFRAG
 void *zmalloc_no_tcache(size_t size) {
+    ASSERT_NO_SIZE_OVERFLOW(size);
     void *ptr = mallocx(size+PREFIX_SIZE, MALLOCX_TCACHE_NONE);
     if (!ptr) zmalloc_oom_handler(size);
     update_zmalloc_stat_alloc(zmalloc_size(ptr));
@@ -147,6 +155,7 @@ void zfree_no_tcache(void *ptr) {
 /* Try allocating memory and zero it, and return NULL if failed.
  * '*usable' is set to the usable size if non NULL. */
 void *ztrycalloc_usable(size_t size, size_t *usable) {
+    ASSERT_NO_SIZE_OVERFLOW(size);
     void *ptr = calloc(1, size+PREFIX_SIZE);
     if (ptr == NULL) return NULL;
 
@@ -187,6 +196,7 @@ void *zcalloc_usable(size_t size, size_t *usable) {
 /* Try reallocating memory, and return NULL if failed.
  * '*usable' is set to the usable size if non NULL. */
 void *ztryrealloc_usable(void *ptr, size_t size, size_t *usable) {
+    ASSERT_NO_SIZE_OVERFLOW(size);
 #ifndef HAVE_MALLOC_SIZE
     void *realptr;
 #endif