sanitize dump payload: fix crash with empty set with listpack encoding (#11519)

The following example will create an empty set (listpack encoding):
```
> RESTORE key 0
"\x14\x25\x25\x00\x00\x00\x00\x00\x02\x01\x82\x5F\x37\x03\x06\x01\x82\x5F\x35\x03\x82\x5F\x33\x03\x00\x01\x82\x5F\x31\x03\x82\x5F\x39\x03\x04\xA9\x08\x01\xFF\x0B\x00\xA3\x26\x49\xB4\x86\xB0\x0F\x41"
OK
> SCARD key
(integer) 0
> SRANDMEMBER key
Error: Server closed the connection
```

In the spirit of #9297, skip empty set when loading RDB_TYPE_SET_LISTPACK.
Introduced in #11290

src/rdb.c

@@ -2319,6 +2319,13 @@ robj *rdbLoadObject(int rdbtype, rio *rdb, sds key, int dbid, int *error) {
                 }
                 o->type = OBJ_SET;
                 o->encoding = OBJ_ENCODING_LISTPACK;
+
+                if (setTypeSize(o) == 0) {
+                    zfree(encoded);
+                    o->ptr = NULL;
+                    decrRefCount(o);
+                    goto emptykey;
+                }
                 if (setTypeSize(o) > server.set_max_listpack_entries)
                     setTypeConvert(o, OBJ_ENCODING_HT);
                 break;

src/rdb.h

@@ -158,7 +158,7 @@ void rdbRemoveTempFile(pid_t childpid, int from_signal);
 int rdbSave(int req, char *filename, rdbSaveInfo *rsi);
 ssize_t rdbSaveObject(rio *rdb, robj *o, robj *key, int dbid);
 size_t rdbSavedObjectLen(robj *o, robj *key, int dbid);
-robj *rdbLoadObject(int type, rio *rdb, sds key, int dbid, int *error);
+robj *rdbLoadObject(int rdbtype, rio *rdb, sds key, int dbid, int *error);
 void backgroundSaveDoneHandler(int exitcode, int bysignal);
 int rdbSaveKeyValuePair(rio *rdb, robj *key, robj *val, long long expiretime,int dbid);
 ssize_t rdbSaveSingleModuleAux(rio *rdb, int when, moduleType *mt);

tests/integration/corrupt-dump-fuzzer.tcl

@@ -1,4 +1,4 @@
-# tests of corrupt ziplist payload with valid CRC
+# tests of corrupt listpack payload with valid CRC
 
 tags {"dump" "corruption" "external:skip"} {
 
@@ -32,6 +32,7 @@ proc generate_collections {suffix elements} {
 proc generate_types {} {
     r config set list-max-ziplist-size 5
     r config set hash-max-ziplist-entries 5
+    r config set set-max-listpack-entries 5
     r config set zset-max-ziplist-entries 5
     r config set stream-node-max-entries 5
 

tests/integration/corrupt-dump.tcl

@@ -800,6 +800,15 @@ test {corrupt payload: fuzzer findings - valgrind fishy value warning} {
     }
 }
 
+test {corrupt payload: fuzzer findings - empty set listpack} {
+    start_server [list overrides [list loglevel verbose use-exit-on-panic yes crash-memcheck-enabled no] ] {
+        r config set sanitize-dump-payload no
+        r debug set-skip-checksum-validation 1
+        catch {r restore _key 0 "\x14\x25\x25\x00\x00\x00\x00\x00\x02\x01\x82\x5F\x37\x03\x06\x01\x82\x5F\x35\x03\x82\x5F\x33\x03\x00\x01\x82\x5F\x31\x03\x82\x5F\x39\x03\x04\xA9\x08\x01\xFF\x0B\x00\xA3\x26\x49\xB4\x86\xB0\x0F\x41"} err
+        assert_match "*Bad data format*" $err
+        r ping
+    }
+}
 
 } ;# tags