Blame SOURCES/kvm-CVE-2015-1779-incrementally-decode-websocket-frames.patch

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From 67c87cd508385158a8a0fb12a430dd19d2883974 Mon Sep 17 00:00:00 2001
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From: Gerd Hoffmann <kraxel@redhat.com>
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Date: Wed, 20 May 2015 08:39:08 +0200
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Subject: [PATCH 1/6] CVE-2015-1779: incrementally decode websocket frames
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Message-id: <1432111149-11644-2-git-send-email-kraxel@redhat.com>
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Patchwork-id: 65099
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O-Subject: [RHEL-7.2 qemu-kvm PATCH 1/2] CVE-2015-1779: incrementally decode websocket frames
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Bugzilla: 1206497
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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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RH-Acked-by: Daniel P. Berrange <berrange@redhat.com>
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From: "Daniel P. Berrange" <berrange@redhat.com>
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The logic for decoding websocket frames wants to fully
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decode the frame header and payload, before allowing the
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VNC server to see any of the payload data. There is no
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size limit on websocket payloads, so this allows a
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malicious network client to consume 2^64 bytes in memory
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in QEMU. It can trigger this denial of service before
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the VNC server even performs any authentication.
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The fix is to decode the header, and then incrementally
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decode the payload data as it is needed. With this fix
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the websocket decoder will allow at most 4k of data to
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be buffered before decoding and processing payload.
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Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
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[ kraxel: fix frequent spurious disconnects, suggested by Peter Maydell ]
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  @@ -361,7 +361,7 @@ int vncws_decode_frame_payload(Buffer *input,
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  -        *payload_size = input->offset;
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  +        *payload_size = *payload_remain;
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[ kraxel: fix 32bit build ]
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  @@ -306,7 +306,7 @@ struct VncState
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  -    uint64_t ws_payload_remain;
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  +    size_t ws_payload_remain;
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Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
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(cherry picked from commit a2bebfd6e09d285aa793cae3fb0fc3a39a9fee6e)
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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 ui/vnc-ws.c | 105 ++++++++++++++++++++++++++++++++++++++++--------------------
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 ui/vnc-ws.h |   9 ++++--
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 ui/vnc.h    |   2 ++
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 3 files changed, 80 insertions(+), 36 deletions(-)
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diff --git a/ui/vnc-ws.c b/ui/vnc-ws.c
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index df89315..a7d457c 100644
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--- a/ui/vnc-ws.c
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+++ b/ui/vnc-ws.c
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@@ -114,7 +114,7 @@ long vnc_client_read_ws(VncState *vs)
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 {
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     int ret, err;
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     uint8_t *payload;
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-    size_t payload_size, frame_size;
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+    size_t payload_size, header_size;
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     VNC_DEBUG("Read websocket %p size %zd offset %zd\n", vs->ws_input.buffer,
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             vs->ws_input.capacity, vs->ws_input.offset);
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     buffer_reserve(&vs->ws_input, 4096);
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@@ -124,18 +124,39 @@ long vnc_client_read_ws(VncState *vs)
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     }
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     vs->ws_input.offset += ret;
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-    /* make sure that nothing is left in the ws_input buffer */
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+    ret = 0;
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+    /* consume as much of ws_input buffer as possible */
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     do {
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-        err = vncws_decode_frame(&vs->ws_input, &payload,
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-                              &payload_size, &frame_size);
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-        if (err <= 0) {
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-            return err;
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+        if (vs->ws_payload_remain == 0) {
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+            err = vncws_decode_frame_header(&vs->ws_input,
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+                                            &header_size,
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+                                            &vs->ws_payload_remain,
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+                                            &vs->ws_payload_mask);
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+            if (err <= 0) {
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+                return err;
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+            }
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+
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+            buffer_advance(&vs->ws_input, header_size);
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         }
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+        if (vs->ws_payload_remain != 0) {
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+            err = vncws_decode_frame_payload(&vs->ws_input,
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+                                             &vs->ws_payload_remain,
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+                                             &vs->ws_payload_mask,
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+                                             &payload,
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+                                             &payload_size);
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+            if (err < 0) {
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+                return err;
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+            }
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+            if (err == 0) {
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+                return ret;
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+            }
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+            ret += err;
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-        buffer_reserve(&vs->input, payload_size);
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-        buffer_append(&vs->input, payload, payload_size);
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+            buffer_reserve(&vs->input, payload_size);
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+            buffer_append(&vs->input, payload, payload_size);
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-        buffer_advance(&vs->ws_input, frame_size);
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+            buffer_advance(&vs->ws_input, payload_size);
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+        }
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     } while (vs->ws_input.offset > 0);
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     return ret;
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@@ -273,15 +294,14 @@ void vncws_encode_frame(Buffer *output, const void *payload,
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     buffer_append(output, payload, payload_size);
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 }
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-int vncws_decode_frame(Buffer *input, uint8_t **payload,
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-                           size_t *payload_size, size_t *frame_size)
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+int vncws_decode_frame_header(Buffer *input,
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+                              size_t *header_size,
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+                              size_t *payload_remain,
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+                              WsMask *payload_mask)
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 {
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     unsigned char opcode = 0, fin = 0, has_mask = 0;
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-    size_t header_size = 0;
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-    uint32_t *payload32;
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+    size_t payload_len;
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     WsHeader *header = (WsHeader *)input->buffer;
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-    WsMask mask;
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-    int i;
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     if (input->offset < WS_HEAD_MIN_LEN + 4) {
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         /* header not complete */
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@@ -291,7 +311,7 @@ int vncws_decode_frame(Buffer *input, uint8_t **payload,
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     fin = (header->b0 & 0x80) >> 7;
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     opcode = header->b0 & 0x0f;
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     has_mask = (header->b1 & 0x80) >> 7;
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-    *payload_size = header->b1 & 0x7f;
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+    payload_len = header->b1 & 0x7f;
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     if (opcode == WS_OPCODE_CLOSE) {
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         /* disconnect */
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@@ -308,40 +328,57 @@ int vncws_decode_frame(Buffer *input, uint8_t **payload,
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         return -2;
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     }
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-    if (*payload_size < 126) {
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-        header_size = 6;
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-        mask = header->u.m;
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-    } else if (*payload_size == 126 && input->offset >= 8) {
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-        *payload_size = be16_to_cpu(header->u.s16.l16);
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-        header_size = 8;
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-        mask = header->u.s16.m16;
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-    } else if (*payload_size == 127 && input->offset >= 14) {
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-        *payload_size = be64_to_cpu(header->u.s64.l64);
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-        header_size = 14;
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-        mask = header->u.s64.m64;
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+    if (payload_len < 126) {
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+        *payload_remain = payload_len;
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+        *header_size = 6;
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+        *payload_mask = header->u.m;
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+    } else if (payload_len == 126 && input->offset >= 8) {
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+        *payload_remain = be16_to_cpu(header->u.s16.l16);
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+        *header_size = 8;
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+        *payload_mask = header->u.s16.m16;
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+    } else if (payload_len == 127 && input->offset >= 14) {
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+        *payload_remain = be64_to_cpu(header->u.s64.l64);
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+        *header_size = 14;
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+        *payload_mask = header->u.s64.m64;
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     } else {
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         /* header not complete */
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         return 0;
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     }
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-    *frame_size = header_size + *payload_size;
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+    return 1;
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+}
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+
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+int vncws_decode_frame_payload(Buffer *input,
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+                               size_t *payload_remain, WsMask *payload_mask,
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+                               uint8_t **payload, size_t *payload_size)
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+{
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+    size_t i;
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+    uint32_t *payload32;
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-    if (input->offset < *frame_size) {
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-        /* frame not complete */
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+    *payload = input->buffer;
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+    /* If we aren't at the end of the payload, then drop
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+     * off the last bytes, so we're always multiple of 4
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+     * for purpose of unmasking, except at end of payload
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+     */
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+    if (input->offset < *payload_remain) {
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+        *payload_size = input->offset - (input->offset % 4);
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+    } else {
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+        *payload_size = *payload_remain;
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+    }
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+    if (*payload_size == 0) {
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         return 0;
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     }
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-
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-    *payload = input->buffer + header_size;
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+    *payload_remain -= *payload_size;
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     /* unmask frame */
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     /* process 1 frame (32 bit op) */
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     payload32 = (uint32_t *)(*payload);
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     for (i = 0; i < *payload_size / 4; i++) {
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-        payload32[i] ^= mask.u;
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+        payload32[i] ^= payload_mask->u;
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     }
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     /* process the remaining bytes (if any) */
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     for (i *= 4; i < *payload_size; i++) {
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-        (*payload)[i] ^= mask.c[i % 4];
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+        (*payload)[i] ^= payload_mask->c[i % 4];
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     }
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     return 1;
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diff --git a/ui/vnc-ws.h b/ui/vnc-ws.h
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index 95c1b0a..6e93fa0 100644
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--- a/ui/vnc-ws.h
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+++ b/ui/vnc-ws.h
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@@ -83,7 +83,12 @@ long vnc_client_read_ws(VncState *vs);
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 void vncws_process_handshake(VncState *vs, uint8_t *line, size_t size);
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 void vncws_encode_frame(Buffer *output, const void *payload,
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             const size_t payload_size);
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-int vncws_decode_frame(Buffer *input, uint8_t **payload,
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-                               size_t *payload_size, size_t *frame_size);
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+int vncws_decode_frame_header(Buffer *input,
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+                              size_t *header_size,
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+                              size_t *payload_remain,
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+                              WsMask *payload_mask);
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+int vncws_decode_frame_payload(Buffer *input,
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+                               size_t *payload_remain, WsMask *payload_mask,
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+                               uint8_t **payload, size_t *payload_size);
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 #endif /* __QEMU_UI_VNC_WS_H */
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diff --git a/ui/vnc.h b/ui/vnc.h
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index 6e99213..0efc5c6 100644
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--- a/ui/vnc.h
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+++ b/ui/vnc.h
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@@ -290,6 +290,8 @@ struct VncState
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 #ifdef CONFIG_VNC_WS
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     Buffer ws_input;
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     Buffer ws_output;
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+    size_t ws_payload_remain;
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+    WsMask ws_payload_mask;
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 #endif
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     /* current output mode information */
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     VncWritePixels *write_pixels;
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-- 
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1.8.3.1
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