By default prevent cross slot operations in functions and scripts with # (#10615)

Adds the `allow-cross-slot-keys` flag to Eval scripts and Functions to allow
scripts to access keys from multiple slots.
The default behavior is now that they are not allowed to do that (unlike before).
This is a breaking change for 7.0 release candidates (to be part of 7.0.0), but
not for previous redis releases since EVAL without shebang isn't doing this check.

Note that the check is done on both the keys declared by the EVAL / FCALL command
arguments, and also the ones used by the script when making a `redis.call`.

A note about the implementation, there seems to have been some confusion
about allowing access to non local keys. I thought I missed something in our
wider conversation, but Redis scripts do block access to non-local keys.
So the issue was just about cross slots being accessed.

5 files changed, 29 insertions, 6 deletions

diff --git a/src/networking.c b/src/networking.c
index d9d300ac2..e79b18d70 100644
--- a/src/networking.c
+++ b/src/networking.c
@@ -160,6 +160,7 @@ client *createClient(connection *conn) {
     c->bulklen = -1;
     c->sentlen = 0;
     c->flags = 0;
+    c->slot = -1;
     c->ctime = c->lastinteraction = server.unixtime;
     clientSetDefaultAuth(c);
     c->replstate = REPL_STATE_NONE;
@@ -2026,6 +2027,7 @@ void resetClient(client *c) {
     c->reqtype = 0;
     c->multibulklen = 0;
     c->bulklen = -1;
+    c->slot = -1;
 
     if (c->deferred_reply_errors)
         listRelease(c->deferred_reply_errors);
diff --git a/src/script.c b/src/script.c
index f3b7b4bb3..8216b47f5 100644
--- a/src/script.c
+++ b/src/script.c
@@ -36,6 +36,7 @@ scriptFlag scripts_flags_def[] = {
     {.flag = SCRIPT_FLAG_ALLOW_OOM, .str = "allow-oom"},
     {.flag = SCRIPT_FLAG_ALLOW_STALE, .str = "allow-stale"},
     {.flag = SCRIPT_FLAG_NO_CLUSTER, .str = "no-cluster"},
+    {.flag = SCRIPT_FLAG_ALLOW_CROSS_SLOT, .str = "allow-cross-slot-keys"},
     {.flag = 0, .str = NULL}, /* flags array end */
 };
 
@@ -218,6 +219,10 @@ int scriptPrepareForRun(scriptRunCtx *run_ctx, client *engine_client, client *ca
         run_ctx->flags |= SCRIPT_ALLOW_OOM;
     }
 
+    if ((script_flags & SCRIPT_FLAG_EVAL_COMPAT_MODE) || (script_flags & SCRIPT_FLAG_ALLOW_CROSS_SLOT)) {
+        run_ctx->flags |= SCRIPT_ALLOW_CROSS_SLOT;
+    }
+
     /* set the curr_run_ctx so we can use it to kill the script if needed */
     curr_run_ctx = run_ctx;
 
@@ -391,7 +396,7 @@ static int scriptVerifyOOM(scriptRunCtx *run_ctx, char **err) {
     return C_OK;
 }
 
-static int scriptVerifyClusterState(client *c, client *original_c, sds *err) {
+static int scriptVerifyClusterState(scriptRunCtx *run_ctx, client *c, client *original_c, sds *err) {
     if (!server.cluster_enabled || mustObeyClient(original_c)) {
         return C_OK;
     }
@@ -402,7 +407,8 @@ static int scriptVerifyClusterState(client *c, client *original_c, sds *err) {
     /* Duplicate relevant flags in the script client. */
     c->flags &= ~(CLIENT_READONLY | CLIENT_ASKING);
     c->flags |= original_c->flags & (CLIENT_READONLY | CLIENT_ASKING);
-    if (getNodeByQuery(c, c->cmd, c->argv, c->argc, NULL, &error_code) != server.cluster->myself) {
+    int hashslot = -1;
+    if (getNodeByQuery(c, c->cmd, c->argv, c->argc, &hashslot, &error_code) != server.cluster->myself) {
         if (error_code == CLUSTER_REDIR_DOWN_RO_STATE) {
             *err = sdsnew(
                     "Script attempted to execute a write command while the "
@@ -416,6 +422,19 @@ static int scriptVerifyClusterState(client *c, client *original_c, sds *err) {
         }
         return C_ERR;
     }
+
+    /* If the script declared keys in advanced, the cross slot error would have
+     * already been thrown. This is only checking for cross slot keys being accessed
+     * that weren't pre-declared. */
+    if (hashslot != -1 && !(run_ctx->flags & SCRIPT_ALLOW_CROSS_SLOT)) {
+        if (original_c->slot == -1) {
+            original_c->slot = hashslot;
+        } else if (original_c->slot != hashslot) {
+            *err = sdsnew("Script attempted to access keys that do not hash to "
+                    "the same slot");
+            return C_ERR;
+        }
+    }
     return C_OK;
 }
 
@@ -520,7 +539,7 @@ void scriptCall(scriptRunCtx *run_ctx, robj* *argv, int argc, sds *err) {
         run_ctx->flags |= SCRIPT_WRITE_DIRTY;
     }
 
-    if (scriptVerifyClusterState(c, run_ctx->original_client, err) != C_OK) {
+    if (scriptVerifyClusterState(run_ctx, c, run_ctx->original_client, err) != C_OK) {
         goto error;
     }
 
diff --git a/src/script.h b/src/script.h
index 9785af095..d855c80e2 100644
--- a/src/script.h
+++ b/src/script.h
@@ -64,6 +64,7 @@
 #define SCRIPT_READ_ONLY              (1ULL<<5) /* indicate that the current script should only perform read commands */
 #define SCRIPT_ALLOW_OOM              (1ULL<<6) /* indicate to allow any command even if OOM reached */
 #define SCRIPT_EVAL_MODE              (1ULL<<7) /* Indicate that the current script called from legacy Lua */
+#define SCRIPT_ALLOW_CROSS_SLOT       (1ULL<<8) /* Indicate that the current script may access keys from multiple slots */
 typedef struct scriptRunCtx scriptRunCtx;
 
 struct scriptRunCtx {
@@ -82,6 +83,7 @@ struct scriptRunCtx {
 #define SCRIPT_FLAG_ALLOW_STALE      (1ULL<<2)
 #define SCRIPT_FLAG_NO_CLUSTER       (1ULL<<3)
 #define SCRIPT_FLAG_EVAL_COMPAT_MODE (1ULL<<4) /* EVAL Script backwards compatible behavior, no shebang provided */
+#define SCRIPT_FLAG_ALLOW_CROSS_SLOT (1ULL<<5)
 
 /* Defines a script flags */
 typedef struct scriptFlag {
diff --git a/src/server.c b/src/server.c
index 47907a4bd..c603af02e 100644
--- a/src/server.c
+++ b/src/server.c
@@ -3676,17 +3676,16 @@ int processCommand(client *c) {
         !(!(c->cmd->flags&CMD_MOVABLE_KEYS) && c->cmd->key_specs_num == 0 &&
           c->cmd->proc != execCommand))
     {
-        int hashslot;
         int error_code;
         clusterNode *n = getNodeByQuery(c,c->cmd,c->argv,c->argc,
-                                        &hashslot,&error_code);
+                                        &c->slot,&error_code);
         if (n == NULL || n != server.cluster->myself) {
             if (c->cmd->proc == execCommand) {
                 discardTransaction(c);
             } else {
                 flagTransaction(c);
             }
-            clusterRedirectClient(c,n,hashslot,error_code);
+            clusterRedirectClient(c,n,c->slot,error_code);
             c->cmd->rejected_calls++;
             return C_OK;
         }
diff --git a/src/server.h b/src/server.h
index da4a1ebcd..ef0215fe0 100644
--- a/src/server.h
+++ b/src/server.h
@@ -1107,6 +1107,7 @@ typedef struct client {
                                buffer or object being sent. */
     time_t ctime;           /* Client creation time. */
     long duration;          /* Current command duration. Used for measuring latency of blocking/non-blocking cmds */
+    int slot;               /* The slot the client is executing against. Set to -1 if no slot is being used */
     time_t lastinteraction; /* Time of the last interaction, used for timeout */
     time_t obuf_soft_limit_reached_time;
     uint64_t flags;         /* Client flags: CLIENT_* macros. */