Fix SSL crash on SSL_write retry

When SSL wants the app to retry, it stands to reason that the local write buffer needs to be grown (read: reallocated) to hold the application bytes. At that point, the buffer is no longer where it was originally. This fixes segfaults.

Fix SSL crash on SSL_write retry
When SSL wants the app to retry, it stands to reason that the local write buffer needs to be grown (read: reallocated) to hold the application bytes. At that point, the buffer is no longer where it was originally. This fixes segfaults.
Wiebe Cazemier
1 parent 8609c607
Showing 3 changed files with 15 additions and 11 deletions
iowrapper.cpp
iowrapper.h
listener.cpp
@@ -22,8 +22,8 @@ License along with FlashMQ. If not, see &lt;https://www.gnu.org/licenses/&gt;.
 #include "logger.h"
 #include "client.h"
-IncompleteSslWrite::IncompleteSslWrite(const void *buf, size_t nbytes) :
-    buf(buf),
+IncompleteSslWrite::IncompleteSslWrite(size_t nbytes) :
+    valid(true),
     nbytes(nbytes)
 {
@@ -31,13 +31,13 @@ IncompleteSslWrite::IncompleteSslWrite(const void *buf, size_t nbytes) :
 void IncompleteSslWrite::reset()
 {
-    buf = nullptr;
+    valid = false;
     nbytes = 0;
 }
 bool IncompleteSslWrite::hasPendingWrite() const
 {
-    return buf != nullptr;
+    return valid;
 }
 void IncompleteWebsocketRead::reset()
@@ -264,7 +264,6 @@ ssize_t IoWrapper::writeOrSslWrite(int fd, const void *buf, size_t nbytes, IoWra
     }
     else
     {
-        const void *buf_ = buf;
         size_t nbytes_ = nbytes;
         /*
@@ -273,7 +272,6 @@ ssize_t IoWrapper::writeOrSslWrite(int fd, const void *buf, size_t nbytes, IoWra
          */
         if (this->incompleteSslWrite.hasPendingWrite())
         {
-            buf_ = this->incompleteSslWrite.buf;
             nbytes_ = this->incompleteSslWrite.nbytes;
         }
@@ -285,7 +283,7 @@ ssize_t IoWrapper::writeOrSslWrite(int fd, const void *buf, size_t nbytes, IoWra
         ERR_clear_error();
         char sslErrorBuf[OPENSSL_ERROR_STRING_SIZE];
-        n = SSL_write(ssl, buf_, nbytes_);
+        n = SSL_write(ssl, buf, nbytes_);
         if (n <= 0)
         {
@@ -295,7 +293,7 @@ ssize_t IoWrapper::writeOrSslWrite(int fd, const void *buf, size_t nbytes, IoWra
             {
                 logger->logf(LOG_DEBUG, "SSL Write is incomplete: %d. Will be retried later.", err);
                 *error = IoWrapResult::Wouldblock;
-                IncompleteSslWrite sslAction(buf_, nbytes_);
+                IncompleteSslWrite sslAction(nbytes_);
                 this->incompleteSslWrite = sslAction;
                 if (err == SSL_ERROR_WANT_READ)
                     this->sslWriteWantsRead = true;
@@ -56,17 +56,21 @@ enum class WebsocketOpcode
     Unknown = 0xF
 };
-/*
+/**
+ * @brief The IncompleteSslWrite struct facilities the SSL retry
+ *
  * OpenSSL doc: "When a write function call has to be repeated because SSL_get_error(3) returned
  * SSL_ERROR_WANT_READ or SSL_ERROR_WANT_WRITE, it must be repeated with the same arguments"
+ *
+ * Note that we use SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER.
  */
 struct IncompleteSslWrite
 {
-    const void *buf = nullptr;
+    bool valid = false;
     size_t nbytes = 0;
     IncompleteSslWrite() = default;
-    IncompleteSslWrite(const void *buf, size_t nbytes);
+    IncompleteSslWrite(size_t nbytes);
     bool hasPendingWrite() const;
     void reset();
@@ -86,6 +86,8 @@ void Listener::loadCertAndKeyFromConfig()
         sslctx = std::make_unique<SslCtxManager>();
         SSL_CTX_set_options(sslctx->get(), SSL_OP_NO_SSLv3); // TODO: config option
         SSL_CTX_set_options(sslctx->get(), SSL_OP_NO_TLSv1); // TODO: config option
+
+        SSL_CTX_set_mode(sslctx->get(), SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER);
     }
     if (SSL_CTX_use_certificate_file(sslctx->get(), sslFullchain.c_str(), SSL_FILETYPE_PEM) != 1)