54 lines
2.4 KiB
Diff
54 lines
2.4 KiB
Diff
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References: bsc#962632 CVE-2015-1779
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Subject: CVE-2015-1779: limit size of HTTP headers from websockets clients
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From: Daniel P. Berrange berrange@redhat.com Mon Mar 23 22:58:22 2015 +0000
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Date: Wed Apr 1 17:12:55 2015 +0200:
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Git: 2cdb5e142fb93e875fa53c52864ef5eb8d5d8b41
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The VNC server websockets decoder will read and buffer data from
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websockets clients until it sees the end of the HTTP headers,
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as indicated by \r\n\r\n. In theory this allows a malicious to
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trick QEMU into consuming an arbitrary amount of RAM. In practice,
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because QEMU runs g_strstr_len() across the buffered header data,
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it will spend increasingly long burning CPU time searching for
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the substring match and less & less time reading data. So while
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this does cause arbitrary memory growth, the bigger problem is
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that QEMU will be burning 100% of available CPU time.
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A novnc websockets client typically sends headers of around
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512 bytes in length. As such it is reasonable to place a 4096
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byte limit on the amount of data buffered while searching for
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the end of HTTP headers.
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Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
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Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
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Index: xen-4.6.0-testing/tools/qemu-xen-dir-remote/ui/vnc-ws.c
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===================================================================
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--- xen-4.6.0-testing.orig/tools/qemu-xen-dir-remote/ui/vnc-ws.c
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+++ xen-4.6.0-testing/tools/qemu-xen-dir-remote/ui/vnc-ws.c
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@@ -89,8 +89,11 @@ void vncws_handshake_read(void *opaque)
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VncState *vs = opaque;
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uint8_t *handshake_end;
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long ret;
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- buffer_reserve(&vs->ws_input, 4096);
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- ret = vnc_client_read_buf(vs, buffer_end(&vs->ws_input), 4096);
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+ /* Typical HTTP headers from novnc are 512 bytes, so limiting
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+ * total header size to 4096 is easily enough. */
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+ size_t want = 4096 - vs->ws_input.offset;
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+ buffer_reserve(&vs->ws_input, want);
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+ ret = vnc_client_read_buf(vs, buffer_end(&vs->ws_input), want);
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if (!ret) {
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if (vs->csock == -1) {
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@@ -107,6 +110,9 @@ void vncws_handshake_read(void *opaque)
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vncws_process_handshake(vs, vs->ws_input.buffer, vs->ws_input.offset);
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buffer_advance(&vs->ws_input, handshake_end - vs->ws_input.buffer +
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strlen(WS_HANDSHAKE_END));
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+ } else if (vs->ws_input.offset >= 4096) {
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+ VNC_DEBUG("End of headers not found in first 4096 bytes\n");
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+ vnc_client_error(vs);
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}
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}
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