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

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)

(cherry picked from commit 3d221e81f3b680543e34942579af190b049ff283)

2 files changed, 24 insertions, 0 deletions

diff --git a/src/networking.c b/src/networking.c
index bfaded9b4..2b8588094 100644
--- a/src/networking.c
+++ b/src/networking.c
@@ -1309,6 +1309,10 @@ int processMultibulkBuffer(client *c) {
             addReplyError(c,"Protocol error: invalid multibulk length");
             setProtocolError("invalid mbulk count",c);
             return C_ERR;
+        } else if (ll > 10 && server.requirepass && !c->authenticated) {
+            addReplyError(c, "Protocol error: unauthenticated multibulk length");
+            setProtocolError("unauth mbulk count", c);
+            return C_ERR;
         }
 
         c->qb_pos = (newline-c->querybuf)+2;
@@ -1354,6 +1358,10 @@ int processMultibulkBuffer(client *c) {
                 addReplyError(c,"Protocol error: invalid bulk length");
                 setProtocolError("invalid bulk length",c);
                 return C_ERR;
+            } else if (ll > 16384 && server.requirepass && !c->authenticated) {
+                addReplyError(c, "Protocol error: unauthenticated bulk length");
+                setProtocolError("unauth bulk length", c);
+                return C_ERR;
             }
 
             c->qb_pos = newline-c->querybuf+2;
diff --git a/tests/unit/auth.tcl b/tests/unit/auth.tcl
index 633cda95c..f5da728e8 100644
--- a/tests/unit/auth.tcl
+++ b/tests/unit/auth.tcl
@@ -24,4 +24,20 @@ start_server {tags {"auth"} overrides {requirepass foobar}} {
         r set foo 100
         r incr foo
     } {101}
+
+    test {For unauthenticated clients multibulk and bulk length are limited} {
+        set rr [redis [srv "host"] [srv "port"] 0]
+        $rr write "*100\r\n"
+        $rr flush
+        catch {[$rr read]} e
+        assert_match {*unauthenticated multibulk length*} $e
+        $rr close
+
+        set rr [redis [srv "host"] [srv "port"] 0]
+        $rr write "*1\r\n\$100000000\r\n"
+        $rr flush
+        catch {[$rr read]} e
+        assert_match {*unauthenticated bulk length*} $e
+        $rr close
+    }
 }