SSL: clarified clean shutdown condition

OpenSSL up to 3.0, when a TCP connection is closed by the peer, returns
SSL_ERROR_SYSCALL without an error queue and with errno set to 0.  Since
OpenSSL 3.0 with SSL_OP_IGNORE_UNEXPECTED_EOF, which nginx sets, this is
reported as SSL_ERROR_ZERO_RETURN instead.

Closing a connection without the close_notify alert is incorrect, yet
common enough in the real world to be handled as a non-error condition.
Truncation attacks are expected to be prevented at the protocol level;
notably, they are not possible for HTTP/1.x requests at all, and only
possible for HTTP/1.x responses if neither Content-Length nor chunked
transfer encoding is used.

Previously, "ERR_peek_error() == 0" was used to detect this, which is
too broad: it also matches TCP-level errors, such as ECONNRESET, which
are better reported as errors, the way the plain TCP code does it in
ngx_unix_recv().

Now only a clean TCP close is treated as a clean connection close.  Most
notably, connection resets now result in "SSL_read() failed" errors.

This change is a modified version of a patch by Maxim Dounin.  The
modifications include resolved conflicts and the refined commit log.

Signed-off-by: Sergey Kandaurov <pluknet@nginx.com>
Origin: <https://freenginx.org/hg/nginx/rev/4c0b66b5046f>

diff --git a/src/event/ngx_event_openssl.c b/src/event/ngx_event_openssl.c
index 1f3cbb2bd27ade4947da6711b1c7b51c27080f71..c9f94c982bc16ae11cafb6803afccabe40568a87 100644 (file)
--- a/src/event/ngx_event_openssl.c
+++ b/src/event/ngx_event_openssl.c
@@ -2319,11 +2319,22 @@ ngx_ssl_handshake(ngx_connection_t *c)
 
     err = (sslerr == SSL_ERROR_SYSCALL) ? ngx_errno : 0;
 
+    if (sslerr == SSL_ERROR_SYSCALL && ERR_peek_error() == 0 && err == 0) {
+
+        /*
+         * OpenSSL up to 3.0 returns SSL_ERROR_SYSCALL
+         * without an error queue and with errno set to 0
+         * if connection is closed cleanly
+         */
+
+        sslerr = SSL_ERROR_ZERO_RETURN;
+    }
+
     c->ssl->no_wait_shutdown = 1;
     c->ssl->no_send_shutdown = 1;
     c->read->eof = 1;
 
-    if (sslerr == SSL_ERROR_ZERO_RETURN || ERR_peek_error() == 0) {
+    if (sslerr == SSL_ERROR_ZERO_RETURN) {
         ngx_connection_error(c, err,
                              "peer closed connection in SSL handshake");
 
@@ -2466,11 +2477,22 @@ ngx_ssl_try_early_data(ngx_connection_t *c)
 
     err = (sslerr == SSL_ERROR_SYSCALL) ? ngx_errno : 0;
 
+    if (sslerr == SSL_ERROR_SYSCALL && ERR_peek_error() == 0 && err == 0) {
+
+        /*
+         * OpenSSL up to 3.0 returns SSL_ERROR_SYSCALL
+         * without an error queue and with errno set to 0
+         * if connection is closed cleanly
+         */
+
+        sslerr = SSL_ERROR_ZERO_RETURN;
+    }
+
     c->ssl->no_wait_shutdown = 1;
     c->ssl->no_send_shutdown = 1;
     c->read->eof = 1;
 
-    if (sslerr == SSL_ERROR_ZERO_RETURN || ERR_peek_error() == 0) {
+    if (sslerr == SSL_ERROR_ZERO_RETURN) {
         ngx_connection_error(c, err,
                              "peer closed connection in SSL handshake");
 
@@ -2979,10 +3001,21 @@ ngx_ssl_handle_recv(ngx_connection_t *c, int n)
         return NGX_AGAIN;
     }
 
+    if (sslerr == SSL_ERROR_SYSCALL && ERR_peek_error() == 0 && err == 0) {
+
+        /*
+         * OpenSSL up to 3.0 returns SSL_ERROR_SYSCALL
+         * without an error queue and with errno set to 0
+         * if connection is closed cleanly
+         */
+
+        sslerr = SSL_ERROR_ZERO_RETURN;
+    }
+
     c->ssl->no_wait_shutdown = 1;
     c->ssl->no_send_shutdown = 1;
 
-    if (sslerr == SSL_ERROR_ZERO_RETURN || ERR_peek_error() == 0) {
+    if (sslerr == SSL_ERROR_ZERO_RETURN) {
         ngx_log_debug0(NGX_LOG_DEBUG_EVENT, c->log, 0,
                        "peer shutdown SSL cleanly");
         return NGX_DONE;
@@ -3738,11 +3771,22 @@ ngx_ssl_shutdown(ngx_connection_t *c)
             return NGX_AGAIN;
         }
 
-        if (sslerr == SSL_ERROR_ZERO_RETURN || ERR_peek_error() == 0) {
-            goto done;
+        err = (sslerr == SSL_ERROR_SYSCALL) ? ngx_errno : 0;
+
+        if (sslerr == SSL_ERROR_SYSCALL && ERR_peek_error() == 0 && err == 0) {
+
+            /*
+             * OpenSSL up to 3.0 returns SSL_ERROR_SYSCALL
+             * without an error queue and with errno set to 0
+             * if connection is closed cleanly
+             */
+
+            sslerr = SSL_ERROR_ZERO_RETURN;
         }
 
-        err = (sslerr == SSL_ERROR_SYSCALL) ? ngx_errno : 0;
+        if (sslerr == SSL_ERROR_ZERO_RETURN) {
+            goto done;
+        }
 
         ngx_ssl_connection_error(c, sslerr, err, "SSL_shutdown() failed");