fix(crypto): Only accept forwarded room keys from our own trusted dev…

…ices

crates/matrix-sdk-crypto/src/gossiping/machine.rs

@@ -945,6 +945,21 @@ impl GossipMachine {
         }
     }
 
+    async fn should_accept_forward(
+        &self,
+        info: &GossipRequest,
+        sender_key: Curve25519PublicKey,
+    ) -> Result<bool, CryptoStoreError> {
+        let device =
+            self.store.get_device_from_curve_key(&info.request_recipient, sender_key).await?;
+
+        if let Some(device) = device {
+            Ok(device.user_id() == self.user_id() && device.is_verified())
+        } else {
+            Ok(false)
+        }
+    }
+
     /// Receive a forwarded room key event that was sent using any of our
     /// supported content types.
     async fn receive_supported_keys(
@@ -956,8 +971,22 @@ impl GossipMachine {
         let algorithm = event.content.algorithm();
 
         if let Some(info) = self.get_key_info(event).await? {
-            self.accept_forwarded_room_key(&info, &event.sender, sender_key, algorithm, content)
-                .await
+            if self.should_accept_forward(&info, sender_key).await? {
+                self.accept_forwarded_room_key(&info, &event.sender, sender_key, algorithm, content)
+                    .await
+            } else {
+                warn!(
+                    sender = %event.sender,
+                    %sender_key,
+                    room_id = %content.room_id,
+                    session_id = content.session_id.as_str(),
+                    claimed_sender_key = %content.claimed_sender_key,
+                    "Received a forwarded room key from an unknown device, or \
+                     from a device that the key request recipient doesn't own",
+                );
+
+                Ok(None)
+            }
         } else {
             warn!(
                 sender = %event.sender,