From be39a421218a84183a7e81ef74bd8c7df42d4eb2 Mon Sep 17 00:00:00 2001
From: Evgeny <evgeny@poberezkin.com>
Date: Wed, 30 Sep 2026 07:16:52 +0100
Subject: [PATCH] core: limit the number of skipped keys during remote access
 (#7622)

* core: limit the number of skipped keys during remote access

* simplify

* core: restrict body size for XRCP commands and responses, limit decompressed size (#7616)

Co-authored-by: Evgeny @ SimpleX Chat <259188159+evgeny-simplex@users.noreply.github.com>

---------

Co-authored-by: Evgeny @ SimpleX Chat <259188159+evgeny-simplex@users.noreply.github.com>
---
 src/Simplex/Chat/Remote/Types.hs |  3 +++
 tests/RemoteTests.hs             | 17 +++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/src/Simplex/Chat/Remote/Types.hs b/src/Simplex/Chat/Remote/Types.hs
index 746aa7f566..90ab3b3279 100644
--- a/src/Simplex/Chat/Remote/Types.hs
+++ b/src/Simplex/Chat/Remote/Types.hs
@@ -18,6 +18,7 @@ import Control.Monad (when)
 import qualified Data.Aeson.TH as J
 import Data.ByteString (ByteString)
 import Data.Int (Int64)
+import qualified Data.Map.Strict as M
 import Data.Text (Text)
 import Data.Word (Word16, Word32)
 import Simplex.Chat.Remote.AppVersion
@@ -73,8 +74,10 @@ getRemoteRcvKeys RemoteCrypto {rcvCounter, chainKeys = TSbChainKeys {rcvKey}, sk
       | otherwise = do -- prevCorrId < corrId
           writeTVar rcvCounter corrId
           skipKeys (prevCorrId + 1)
+          modifyTVar' skippedKeys $ \m -> M.drop (M.size m - maxSkippedKeys) m
           Right <$> getKeys
     maxSkip = 256
+    maxSkippedKeys = 1024
     getKeys = (,) <$> stateTVar rcvKey C.sbcHkdf <*> stateTVar rcvKey C.sbcHkdf
     skipKeys !cId =
       when (cId < corrId) $ do
diff --git a/tests/RemoteTests.hs b/tests/RemoteTests.hs
index 3b1cfa1cae..2ab4cae0d6 100644
--- a/tests/RemoteTests.hs
+++ b/tests/RemoteTests.hs
@@ -61,6 +61,23 @@ remoteTests = describe "Remote" $ do
       filter (not . sanitized) fileNames `shouldBe` []
     it "sanitizes to a name with no directory components" $ \_ ->
       filter (not . bareName) fileNames `shouldBe` []
+  describe "skipped keys" $ do
+    it "keeps the most recent skipped keys" $ \_ -> do
+      (_, pk) <- atomically . C.generateKeyPair =<< C.newRandom
+      let (ck, _) = C.sbcInit "" ("secret" :: B.ByteString)
+      sndCounter <- newTVarIO 0
+      rcvCounter <- newTVarIO 0
+      sndKey <- newTVarIO ck
+      rcvKey <- newTVarIO ck
+      skippedKeys <- newTVarIO M.empty
+      let rc = RemoteCrypto {sessionCode = "", sndCounter, rcvCounter, chainKeys = TSbChainKeys {sndKey, rcvKey}, skippedKeys, signatures = RSSign pk pk, compression = False}
+          receive corrId = eitherToMaybe <$> atomically (getRemoteRcvKeys rc corrId)
+      sent <- replicateM 1280 $ atomically $ getRemoteSndKeys rc
+      let sentKeys = M.fromList [(corrId, (cmdKN, fileKN)) | (corrId, cmdKN, fileKN) <- sent]
+      forM_ [256, 512 .. 1280] $ \corrId -> receive corrId `shouldReturn` M.lookup corrId sentKeys
+      M.size <$> readTVarIO skippedKeys `shouldReturn` 1024
+      receive 251 `shouldReturn` Nothing
+      receive 252 `shouldReturn` M.lookup 252 sentKeys
   describe "body size limit" $ do
     it "rejects encrypted body above limit without reading it" $ \_ -> do
       rc <- testRemoteCrypto