Merge #21407: i2p: limit the size of incoming messages

7059e6d82275b44efc41675ee10760145b6c1073 test: add a test to ensure RecvUntilTerminator() limit works (Vasil Dimov)
80a5a8ea2b7ad512c74c29df5b504e9be6cf23a0 i2p: limit the size of incoming messages (Vasil Dimov)

Pull request description:

  Put a limit on the amount of data `Sock::RecvUntilTerminator()` can read
  if no terminator is received.

  In the case of I2P this avoids a runaway (or malicious) I2P proxy
  sending us tons of data without a terminator before a timeout is
  triggered.

ACKs for top commit:
  laanwj:
    Re-ACK 7059e6d82275b44efc41675ee10760145b6c1073

Tree-SHA512: 21f3f3468c765c726cdc877eae847cdb4dbe225d94c5bd1849bd752c9761fac881c554f16ea7a685ad40312159d554e126c481e21c5fd83a6d947060b920373d

2 files changed, 12 insertions, 3 deletions

diff --git a/src/util/sock.cpp b/src/util/sock.cpp
index e13c52a16a..f9ecfef5d4 100644
--- a/src/util/sock.cpp
+++ b/src/util/sock.cpp
@@ -175,7 +175,8 @@ void Sock::SendComplete(const std::string& data,
 
 std::string Sock::RecvUntilTerminator(uint8_t terminator,
                                       std::chrono::milliseconds timeout,
-                                      CThreadInterrupt& interrupt) const
+                                      CThreadInterrupt& interrupt,
+                                      size_t max_data) const
 {
     const auto deadline = GetTime<std::chrono::milliseconds>() + timeout;
     std::string data;
@@ -190,9 +191,14 @@ std::string Sock::RecvUntilTerminator(uint8_t terminator,
     // at a time is about 50 times slower.
 
     for (;;) {
+        if (data.size() >= max_data) {
+            throw std::runtime_error(
+                strprintf("Received too many bytes without a terminator (%u)", data.size()));
+        }
+
         char buf[512];
 
-        const ssize_t peek_ret{Recv(buf, sizeof(buf), MSG_PEEK)};
+        const ssize_t peek_ret{Recv(buf, std::min(sizeof(buf), max_data - data.size()), MSG_PEEK)};
 
         switch (peek_ret) {
         case -1: {
diff --git a/src/util/sock.h b/src/util/sock.h
index ecebb84205..4b0618dcff 100644
--- a/src/util/sock.h
+++ b/src/util/sock.h
@@ -135,13 +135,16 @@ public:
      * @param[in] terminator Character up to which to read from the socket.
      * @param[in] timeout Timeout for the entire operation.
      * @param[in] interrupt If this is signaled then the operation is canceled.
+     * @param[in] max_data The maximum amount of data (in bytes) to receive. If this many bytes
+     * are received and there is still no terminator, then this method will throw an exception.
      * @return The data that has been read, without the terminating character.
      * @throws std::runtime_error if the operation cannot be completed. In this case some bytes may
      * have been consumed from the socket.
      */
     virtual std::string RecvUntilTerminator(uint8_t terminator,
                                             std::chrono::milliseconds timeout,
-                                            CThreadInterrupt& interrupt) const;
+                                            CThreadInterrupt& interrupt,
+                                            size_t max_data) const;
 
     /**
      * Check if still connected.