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From 7721e2e58f7cd2fcf835800622b8a7e1cdeb4557 Mon Sep 17 00:00:00 2001
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From: Gerd Hoffmann <kraxel@redhat.com>
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Date: Tue, 22 Sep 2015 17:44:54 +0200
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Subject: [PATCH 2/2] CVE-2015-1779: limit size of HTTP headers from websockets
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clients
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Message-id: <1442943894-7638-3-git-send-email-kraxel@redhat.com>
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Patchwork-id: 67885
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O-Subject: [RHEL-7.1.z qemu-kvm PATCH 2/2] CVE-2015-1779: limit size of HTTP headers from websockets clients
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Bugzilla: 1205050
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RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
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RH-Acked-by: Thomas Huth <thuth@redhat.com>
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RH-Acked-by: Petr Matousek <pmatouse@redhat.com>
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From: "Daniel P. Berrange" <berrange@redhat.com>
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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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(cherry picked from commit 2cdb5e142fb93e875fa53c52864ef5eb8d5d8b41)
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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ui/vnc-ws.c | 10 ++++++++--
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1 file changed, 8 insertions(+), 2 deletions(-)
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diff --git a/ui/vnc-ws.c b/ui/vnc-ws.c
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index a7d457c..7133be9 100644
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--- a/ui/vnc-ws.c
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+++ b/ui/vnc-ws.c
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@@ -88,8 +88,11 @@ 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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@@ -106,6 +109,9 @@ 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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--
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1.8.3.1
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