Fix occasional RM_Call() crashes. (#9805)

With dynamically growing argc (#9528), it is necessary to initialize
argv_len. Normally createClient() handles that, but in the case of a
module shared_client, this needs to be done explicitly.

This also addresses an issue with rewriteClientCommandArgument() which
doesn't properly handle the case where the new element extends beyond
argc but not beyond argv_len.

src/module.c

@@ -394,7 +394,7 @@ typedef struct RedisModuleKeyOptCtx {
 void RM_FreeCallReply(RedisModuleCallReply *reply);
 void RM_CloseKey(RedisModuleKey *key);
 void autoMemoryCollect(RedisModuleCtx *ctx);
-robj **moduleCreateArgvFromUserFormat(const char *cmdname, const char *fmt, int *argcp, int *flags, va_list ap);
+robj **moduleCreateArgvFromUserFormat(const char *cmdname, const char *fmt, int *argcp, int *argvlenp, int *flags, va_list ap);
 void moduleReplicateMultiIfNeeded(RedisModuleCtx *ctx);
 void RM_ZsetRangeStop(RedisModuleKey *kp);
 static void zsetKeyReset(RedisModuleKey *key);
@@ -2400,7 +2400,7 @@ int RM_Replicate(RedisModuleCtx *ctx, const char *cmdname, const char *fmt, ...)
 
     /* Create the client and dispatch the command. */
     va_start(ap, fmt);
-    argv = moduleCreateArgvFromUserFormat(cmdname,fmt,&argc,&flags,ap);
+    argv = moduleCreateArgvFromUserFormat(cmdname,fmt,&argc,NULL,&flags,ap);
     va_end(ap);
     if (argv == NULL) return REDISMODULE_ERR;
 
@@ -4765,9 +4765,9 @@ RedisModuleString *RM_CreateStringFromCallReply(RedisModuleCallReply *reply) {
     }
 }
 
-/* Returns an array of robj pointers, and populates *argc with the number
- * of items, by parsing the format specifier "fmt" as described for
- * the RM_Call(), RM_Replicate() and other module APIs.
+/* Returns an array of robj pointers, by parsing the format specifier "fmt" as described for
+ * the RM_Call(), RM_Replicate() and other module APIs. Populates *argcp with the number of
+ * items and *argvlenp with the length of the allocated argv.
  *
  * The integer pointed by 'flags' is populated with flags according
  * to special modifiers in "fmt". For now only one exists:
@@ -4781,7 +4781,7 @@ RedisModuleString *RM_CreateStringFromCallReply(RedisModuleCallReply *reply) {
  *
  * On error (format specifier error) NULL is returned and nothing is
  * allocated. On success the argument vector is returned. */
-robj **moduleCreateArgvFromUserFormat(const char *cmdname, const char *fmt, int *argcp, int *flags, va_list ap) {
+robj **moduleCreateArgvFromUserFormat(const char *cmdname, const char *fmt, int *argcp, int *argvlenp, int *flags, va_list ap) {
     int argc = 0, argv_size, j;
     robj **argv = NULL;
 
@@ -4847,7 +4847,8 @@ robj **moduleCreateArgvFromUserFormat(const char *cmdname, const char *fmt, int
         }
         p++;
     }
-    *argcp = argc;
+    if (argcp) *argcp = argc;
+    if (argvlenp) *argvlenp = argv_size;
     return argv;
 
 fmterr:
@@ -4909,14 +4910,14 @@ RedisModuleCallReply *RM_Call(RedisModuleCtx *ctx, const char *cmdname, const ch
     struct redisCommand *cmd;
     client *c = NULL;
     robj **argv = NULL;
-    int argc = 0, flags = 0;
+    int argc = 0, argv_len = 0, flags = 0;
     va_list ap;
     RedisModuleCallReply *reply = NULL;
     int replicate = 0; /* Replicate this command? */
 
     /* Handle arguments. */
     va_start(ap, fmt);
-    argv = moduleCreateArgvFromUserFormat(cmdname,fmt,&argc,&flags,ap);
+    argv = moduleCreateArgvFromUserFormat(cmdname,fmt,&argc,&argv_len,&flags,ap);
     replicate = flags & REDISMODULE_ARGV_REPLICATE;
     va_end(ap);
 
@@ -4941,6 +4942,7 @@ RedisModuleCallReply *RM_Call(RedisModuleCtx *ctx, const char *cmdname, const ch
     c->db = ctx->client->db;
     c->argv = argv;
     c->argc = argc;
+    c->argv_len = argv_len;
     c->resp = 2;
     if (flags & REDISMODULE_ARGV_RESP_3) {
         c->resp = 3;
@@ -5974,7 +5976,7 @@ void RM_EmitAOF(RedisModuleIO *io, const char *cmdname, const char *fmt, ...) {
 
     /* Emit the arguments into the AOF in Redis protocol format. */
     va_start(ap, fmt);
-    argv = moduleCreateArgvFromUserFormat(cmdname,fmt,&argc,&flags,ap);
+    argv = moduleCreateArgvFromUserFormat(cmdname,fmt,&argc,NULL,&flags,ap);
     va_end(ap);
     if (argv == NULL) {
         serverLog(LL_WARNING,

src/networking.c

@@ -3276,9 +3276,16 @@ void replaceClientCommandVector(client *c, int argc, robj **argv) {
 void rewriteClientCommandArgument(client *c, int i, robj *newval) {
     robj *oldval;
     retainOriginalCommandVector(c);
-    if (i >= c->argv_len) {
-        c->argv = zrealloc(c->argv,sizeof(robj*)*(i+1));
-        c->argc = c->argv_len = i+1;
+
+    /* We need to handle both extending beyond argc (just update it and
+     * initialize the new element) or beyond argv_len (realloc is needed).
+     */
+    if (i >= c->argc) {
+        if (i >= c->argv_len) {
+            c->argv = zrealloc(c->argv,sizeof(robj*)*(i+1));
+            c->argv_len = i+1;
+        }
+        c->argc = i+1;
         c->argv[i] = NULL;
     }
     oldval = c->argv[i];