File CVE-2015-1779-qemuu-limit-size-of-HTTP-headers-... of Package xen.6738

Overview Repositories Revisions Requests Users Attributes Meta

File CVE-2015-1779-qemuu-limit-size-of-HTTP-headers-from-websockets-clients.patch of Package xen.6738

References: bsc#962632 CVE-2015-1779

Subject: CVE-2015-1779: limit size of HTTP headers from websockets clients
From: Daniel P. Berrange berrange@redhat.com Mon Mar 23 22:58:22 2015 +0000
Date: Wed Apr 1 17:12:55 2015 +0200:
Git: 2cdb5e142fb93e875fa53c52864ef5eb8d5d8b41

The VNC server websockets decoder will read and buffer data from
websockets clients until it sees the end of the HTTP headers,
as indicated by \r\n\r\n. In theory this allows a malicious to
trick QEMU into consuming an arbitrary amount of RAM. In practice,
because QEMU runs g_strstr_len() across the buffered header data,
it will spend increasingly long burning CPU time searching for
the substring match and less & less time reading data. So while
this does cause arbitrary memory growth, the bigger problem is
that QEMU will be burning 100% of available CPU time.

A novnc websockets client typically sends headers of around
512 bytes in length. As such it is reasonable to place a 4096
byte limit on the amount of data buffered while searching for
the end of HTTP headers.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

Index: xen-4.4.3-testing/tools/qemu-xen-dir-remote/ui/vnc-ws.c
===================================================================
--- xen-4.4.3-testing.orig/tools/qemu-xen-dir-remote/ui/vnc-ws.c
+++ xen-4.4.3-testing/tools/qemu-xen-dir-remote/ui/vnc-ws.c
@@ -88,8 +88,11 @@ void vncws_handshake_read(void *opaque)
     VncState *vs = opaque;
     uint8_t *handshake_end;
     long ret;
-    buffer_reserve(&vs->ws_input, 4096);
-    ret = vnc_client_read_buf(vs, buffer_end(&vs->ws_input), 4096);
+    /* Typical HTTP headers from novnc are 512 bytes, so limiting
+     * total header size to 4096 is easily enough. */
+    size_t want = 4096 - vs->ws_input.offset;
+    buffer_reserve(&vs->ws_input, want);
+    ret = vnc_client_read_buf(vs, buffer_end(&vs->ws_input), want);
 
     if (!ret) {
         if (vs->csock == -1) {
@@ -106,6 +109,9 @@ void vncws_handshake_read(void *opaque)
         vncws_process_handshake(vs, vs->ws_input.buffer, vs->ws_input.offset);
         buffer_advance(&vs->ws_input, handshake_end - vs->ws_input.buffer +
                 strlen(WS_HANDSHAKE_END));
+    } else if (vs->ws_input.offset >= 4096) {
+        VNC_DEBUG("End of headers not found in first 4096 bytes\n");
+        vnc_client_error(vs);
     }
 }

Places

File CVE-2015-1779-qemuu-limit-size-of-HTTP-headers-from-websockets-clients.patch of Package xen.6738

Places