Prevent unauthenticated client from easily consuming lots of memory (CVE-2021-32675) (#9588)

This change sets a low limit for multibulk and bulk length in the
protocol for unauthenticated connections, so that they can't easily
cause redis to allocate massive amounts of memory by sending just a few
characters on the network.
The new limits are 10 arguments of 16kb each (instead of 1m of 512mb)

1 files changed, 17 insertions, 0 deletions

diff --git a/src/networking.c b/src/networking.c
index 8cfb0e331..9c1b46052 100644
--- a/src/networking.c
+++ b/src/networking.c
@@ -107,6 +107,15 @@ static void clientSetDefaultAuth(client *c) {
                        !(c->user->flags & USER_FLAG_DISABLED);
 }
 
+int authRequired(client *c) {
+    /* Check if the user is authenticated. This check is skipped in case
+     * the default user is flagged as "nopass" and is active. */
+    int auth_required = (!(DefaultUser->flags & USER_FLAG_NOPASS) ||
+                          (DefaultUser->flags & USER_FLAG_DISABLED)) &&
+                        !c->authenticated;
+    return auth_required;
+}
+
 client *createClient(connection *conn) {
     client *c = zmalloc(sizeof(client));
 
@@ -1913,6 +1922,10 @@ int processMultibulkBuffer(client *c) {
             addReplyError(c,"Protocol error: invalid multibulk length");
             setProtocolError("invalid mbulk count",c);
             return C_ERR;
+        } else if (ll > 10 && authRequired(c)) {
+            addReplyError(c, "Protocol error: unauthenticated multibulk length");
+            setProtocolError("unauth mbulk count", c);
+            return C_ERR;
         }
 
         c->qb_pos = (newline-c->querybuf)+2;
@@ -1961,6 +1974,10 @@ int processMultibulkBuffer(client *c) {
                 addReplyError(c,"Protocol error: invalid bulk length");
                 setProtocolError("invalid bulk length",c);
                 return C_ERR;
+            } else if (ll > 16384 && authRequired(c)) {
+                addReplyError(c, "Protocol error: unauthenticated bulk length");
+                setProtocolError("unauth bulk length", c);
+                return C_ERR;
             }
 
             c->qb_pos = newline-c->querybuf+2;