--- /dev/null
+From a2bebfd6e09d285aa793cae3fb0fc3a39a9fee6e Mon Sep 17 00:00:00 2001
+From: "Daniel P. Berrange" <berrange@redhat.com>
+Date: Mon, 23 Mar 2015 22:58:21 +0000
+Subject: [PATCH 1/2] CVE-2015-1779: incrementally decode websocket frames
+
+The logic for decoding websocket frames wants to fully
+decode the frame header and payload, before allowing the
+VNC server to see any of the payload data. There is no
+size limit on websocket payloads, so this allows a
+malicious network client to consume 2^64 bytes in memory
+in QEMU. It can trigger this denial of service before
+the VNC server even performs any authentication.
+
+The fix is to decode the header, and then incrementally
+decode the payload data as it is needed. With this fix
+the websocket decoder will allow at most 4k of data to
+be buffered before decoding and processing payload.
+
+Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
+
+[ kraxel: fix frequent spurious disconnects, suggested by Peter Maydell ]
+
+ @@ -361,7 +361,7 @@ int vncws_decode_frame_payload(Buffer *input,
+ - *payload_size = input->offset;
+ + *payload_size = *payload_remain;
+
+[ kraxel: fix 32bit build ]
+
+ @@ -306,7 +306,7 @@ struct VncState
+ - uint64_t ws_payload_remain;
+ + size_t ws_payload_remain;
+
+Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
+---
+ ui/vnc-ws.c | 105 ++++++++++++++++++++++++++++++++++++++++--------------------
+ ui/vnc-ws.h | 9 ++++--
+ ui/vnc.h | 2 ++
+ 3 files changed, 80 insertions(+), 36 deletions(-)
+
+diff --git a/ui/vnc-ws.c b/ui/vnc-ws.c
+index 85dbb7e..0b7de4e 100644
+--- a/ui/vnc-ws.c
++++ b/ui/vnc-ws.c
+@@ -107,7 +107,7 @@ long vnc_client_read_ws(VncState *vs)
+ {
+ int ret, err;
+ uint8_t *payload;
+- size_t payload_size, frame_size;
++ size_t payload_size, header_size;
+ VNC_DEBUG("Read websocket %p size %zd offset %zd\n", vs->ws_input.buffer,
+ vs->ws_input.capacity, vs->ws_input.offset);
+ buffer_reserve(&vs->ws_input, 4096);
+@@ -117,18 +117,39 @@ long vnc_client_read_ws(VncState *vs)
+ }
+ vs->ws_input.offset += ret;
+
+- /* make sure that nothing is left in the ws_input buffer */
++ ret = 0;
++ /* consume as much of ws_input buffer as possible */
+ do {
+- err = vncws_decode_frame(&vs->ws_input, &payload,
+- &payload_size, &frame_size);
+- if (err <= 0) {
+- return err;
++ if (vs->ws_payload_remain == 0) {
++ err = vncws_decode_frame_header(&vs->ws_input,
++ &header_size,
++ &vs->ws_payload_remain,
++ &vs->ws_payload_mask);
++ if (err <= 0) {
++ return err;
++ }
++
++ buffer_advance(&vs->ws_input, header_size);
+ }
++ if (vs->ws_payload_remain != 0) {
++ err = vncws_decode_frame_payload(&vs->ws_input,
++ &vs->ws_payload_remain,
++ &vs->ws_payload_mask,
++ &payload,
++ &payload_size);
++ if (err < 0) {
++ return err;
++ }
++ if (err == 0) {
++ return ret;
++ }
++ ret += err;
+
+- buffer_reserve(&vs->input, payload_size);
+- buffer_append(&vs->input, payload, payload_size);
++ buffer_reserve(&vs->input, payload_size);
++ buffer_append(&vs->input, payload, payload_size);
+
+- buffer_advance(&vs->ws_input, frame_size);
++ buffer_advance(&vs->ws_input, payload_size);
++ }
+ } while (vs->ws_input.offset > 0);
+
+ return ret;
+@@ -265,15 +286,14 @@ void vncws_encode_frame(Buffer *output, const void *payload,
+ buffer_append(output, payload, payload_size);
+ }
+
+-int vncws_decode_frame(Buffer *input, uint8_t **payload,
+- size_t *payload_size, size_t *frame_size)
++int vncws_decode_frame_header(Buffer *input,
++ size_t *header_size,
++ size_t *payload_remain,
++ WsMask *payload_mask)
+ {
+ unsigned char opcode = 0, fin = 0, has_mask = 0;
+- size_t header_size = 0;
+- uint32_t *payload32;
++ size_t payload_len;
+ WsHeader *header = (WsHeader *)input->buffer;
+- WsMask mask;
+- int i;
+
+ if (input->offset < WS_HEAD_MIN_LEN + 4) {
+ /* header not complete */
+@@ -283,7 +303,7 @@ int vncws_decode_frame(Buffer *input, uint8_t **payload,
+ fin = (header->b0 & 0x80) >> 7;
+ opcode = header->b0 & 0x0f;
+ has_mask = (header->b1 & 0x80) >> 7;
+- *payload_size = header->b1 & 0x7f;
++ payload_len = header->b1 & 0x7f;
+
+ if (opcode == WS_OPCODE_CLOSE) {
+ /* disconnect */
+@@ -300,40 +320,57 @@ int vncws_decode_frame(Buffer *input, uint8_t **payload,
+ return -2;
+ }
+
+- if (*payload_size < 126) {
+- header_size = 6;
+- mask = header->u.m;
+- } else if (*payload_size == 126 && input->offset >= 8) {
+- *payload_size = be16_to_cpu(header->u.s16.l16);
+- header_size = 8;
+- mask = header->u.s16.m16;
+- } else if (*payload_size == 127 && input->offset >= 14) {
+- *payload_size = be64_to_cpu(header->u.s64.l64);
+- header_size = 14;
+- mask = header->u.s64.m64;
++ if (payload_len < 126) {
++ *payload_remain = payload_len;
++ *header_size = 6;
++ *payload_mask = header->u.m;
++ } else if (payload_len == 126 && input->offset >= 8) {
++ *payload_remain = be16_to_cpu(header->u.s16.l16);
++ *header_size = 8;
++ *payload_mask = header->u.s16.m16;
++ } else if (payload_len == 127 && input->offset >= 14) {
++ *payload_remain = be64_to_cpu(header->u.s64.l64);
++ *header_size = 14;
++ *payload_mask = header->u.s64.m64;
+ } else {
+ /* header not complete */
+ return 0;
+ }
+
+- *frame_size = header_size + *payload_size;
++ return 1;
++}
++
++int vncws_decode_frame_payload(Buffer *input,
++ size_t *payload_remain, WsMask *payload_mask,
++ uint8_t **payload, size_t *payload_size)
++{
++ size_t i;
++ uint32_t *payload32;
+
+- if (input->offset < *frame_size) {
+- /* frame not complete */
++ *payload = input->buffer;
++ /* If we aren't at the end of the payload, then drop
++ * off the last bytes, so we're always multiple of 4
++ * for purpose of unmasking, except at end of payload
++ */
++ if (input->offset < *payload_remain) {
++ *payload_size = input->offset - (input->offset % 4);
++ } else {
++ *payload_size = *payload_remain;
++ }
++ if (*payload_size == 0) {
+ return 0;
+ }
+-
+- *payload = input->buffer + header_size;
++ *payload_remain -= *payload_size;
+
+ /* unmask frame */
+ /* process 1 frame (32 bit op) */
+ payload32 = (uint32_t *)(*payload);
+ for (i = 0; i < *payload_size / 4; i++) {
+- payload32[i] ^= mask.u;
++ payload32[i] ^= payload_mask->u;
+ }
+ /* process the remaining bytes (if any) */
+ for (i *= 4; i < *payload_size; i++) {
+- (*payload)[i] ^= mask.c[i % 4];
++ (*payload)[i] ^= payload_mask->c[i % 4];
+ }
+
+ return 1;
+diff --git a/ui/vnc-ws.h b/ui/vnc-ws.h
+index ef229b7..14d4230 100644
+--- a/ui/vnc-ws.h
++++ b/ui/vnc-ws.h
+@@ -83,7 +83,12 @@ long vnc_client_read_ws(VncState *vs);
+ void vncws_process_handshake(VncState *vs, uint8_t *line, size_t size);
+ void vncws_encode_frame(Buffer *output, const void *payload,
+ const size_t payload_size);
+-int vncws_decode_frame(Buffer *input, uint8_t **payload,
+- size_t *payload_size, size_t *frame_size);
++int vncws_decode_frame_header(Buffer *input,
++ size_t *header_size,
++ size_t *payload_remain,
++ WsMask *payload_mask);
++int vncws_decode_frame_payload(Buffer *input,
++ size_t *payload_remain, WsMask *payload_mask,
++ uint8_t **payload, size_t *payload_size);
+
+ #endif /* __QEMU_UI_VNC_WS_H */
+diff --git a/ui/vnc.h b/ui/vnc.h
+index e19ac39..3f7c6a9 100644
+--- a/ui/vnc.h
++++ b/ui/vnc.h
+@@ -306,6 +306,8 @@ struct VncState
+ #ifdef CONFIG_VNC_WS
+ Buffer ws_input;
+ Buffer ws_output;
++ size_t ws_payload_remain;
++ WsMask ws_payload_mask;
+ #endif
+ /* current output mode information */
+ VncWritePixels *write_pixels;
+--
+2.1.4
+
--- /dev/null
+From 2cdb5e142fb93e875fa53c52864ef5eb8d5d8b41 Mon Sep 17 00:00:00 2001
+From: "Daniel P. Berrange" <berrange@redhat.com>
+Date: Mon, 23 Mar 2015 22:58:22 +0000
+Subject: [PATCH 2/2] CVE-2015-1779: limit size of HTTP headers from websockets
+ clients
+
+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>
+---
+ ui/vnc-ws.c | 10 ++++++++--
+ 1 file changed, 8 insertions(+), 2 deletions(-)
+
+diff --git a/ui/vnc-ws.c b/ui/vnc-ws.c
+index 0b7de4e..62eb97f 100644
+--- a/ui/vnc-ws.c
++++ b/ui/vnc-ws.c
+@@ -81,8 +81,11 @@ 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) {
+@@ -99,6 +102,9 @@ 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);
+ }
+ }
+
+--
+2.1.4
+
projects / pve-qemu-kvm.git / commitdiff