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libtdevnc/libvncserver/ws_decode.c

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#include "ws_decode.h"
#include "base64.h"
#include <string.h>
#include <errno.h>
#define WS_HYBI_MASK_LEN 4
#define WS_HYBI_HEADER_LEN_SHORT 2 + WS_HYBI_MASK_LEN
#define WS_HYBI_HEADER_LEN_EXTENDED 4 + WS_HYBI_MASK_LEN
#define WS_HYBI_HEADER_LEN_LONG 10 + WS_HYBI_MASK_LEN
#undef WS_DECODE_DEBUG
/* set to 1 to produce very fine debugging output */
#define WS_DECODE_DEBUG 0
#if WS_DECODE_DEBUG == 1
#define ws_dbg(fmt, ...) rfbLog((fmt), ##__VA_ARGS)
#else
#define ws_dbg(fmt, ...)
#endif
static inline int
isControlFrame(ws_ctx_t *wsctx)
{
return 0 != (wsctx->header.opcode & 0x08);
}
static uint64_t
hybiRemaining(ws_ctx_t *wsctx)
{
return wsctx->header.payloadLen - wsctx->nReadPayload;
}
static void
hybiDecodeCleanupBasics(ws_ctx_t *wsctx)
{
/* keep opcode, cleanup rest */
wsctx->header.opcode = WS_OPCODE_INVALID;
wsctx->header.payloadLen = 0;
wsctx->header.mask.u = 0;
wsctx->header.headerLen = 0;
wsctx->header.data = NULL;
wsctx->header.nRead = 0;
wsctx->nReadPayload = 0;
wsctx->carrylen = 0;
wsctx->readPos = (unsigned char *)wsctx->codeBufDecode;
wsctx->readlen = 0;
wsctx->hybiDecodeState = WS_HYBI_STATE_HEADER_PENDING;
wsctx->writePos = NULL;
}
static void
hybiDecodeCleanupForContinuation(ws_ctx_t *wsctx)
{
hybiDecodeCleanupBasics(wsctx);
ws_dbg("clean up frame, but expect continuation with opcode %d\n", wsctx->continuation_opcode);
}
void
hybiDecodeCleanupComplete(ws_ctx_t *wsctx)
{
hybiDecodeCleanupBasics(wsctx);
wsctx->continuation_opcode = WS_OPCODE_INVALID;
ws_dbg("cleaned up wsctx completely\n");
}
/**
* Return payload data that has been decoded/unmasked from
* a websocket frame.
*
* @param[out] dst destination buffer
* @param[in] len bytes to copy to destination buffer
* @param[in,out] wsctx internal state of decoding procedure
* @param[out] number of bytes actually written to dst buffer
* @return next hybi decoding state
*/
static int
hybiReturnData(char *dst, int len, ws_ctx_t *wsctx, int *nWritten)
{
int nextState = WS_HYBI_STATE_ERR;
/* if we have something already decoded copy and return */
if (wsctx->readlen > 0) {
/* simply return what we have */
if (wsctx->readlen > len) {
ws_dbg("copy to %d bytes to dst buffer; readPos=%p, readLen=%d\n", len, wsctx->readPos, wsctx->readlen);
memcpy(dst, wsctx->readPos, len);
*nWritten = len;
wsctx->readlen -= len;
wsctx->readPos += len;
nextState = WS_HYBI_STATE_DATA_AVAILABLE;
} else {
ws_dbg("copy to %d bytes to dst buffer; readPos=%p, readLen=%d\n", wsctx->readlen, wsctx->readPos, wsctx->readlen);
memcpy(dst, wsctx->readPos, wsctx->readlen);
*nWritten = wsctx->readlen;
wsctx->readlen = 0;
wsctx->readPos = NULL;
if (hybiRemaining(wsctx) == 0) {
nextState = WS_HYBI_STATE_FRAME_COMPLETE;
} else {
nextState = WS_HYBI_STATE_DATA_NEEDED;
}
}
ws_dbg("after copy: readPos=%p, readLen=%d\n", wsctx->readPos, wsctx->readlen);
} else {
/* it may happen that we read some bytes but could not decode them,
* in that case, set errno to EAGAIN and return -1 */
nextState = wsctx->hybiDecodeState;
errno = EAGAIN;
*nWritten = -1;
}
return nextState;
}
/**
* Read an RFC 6455 websocket frame (IETF hybi working group).
*
* Internal state is updated according to bytes received and the
* decoding of header information.
*
* @param[in] cl client ptr with ptr to raw socket and ws_ctx_t ptr
* @param[out] sockRet emulated recv return value
* @param[out] nPayload number of payload bytes already read
* @return next hybi decoding state; WS_HYBI_STATE_HEADER_PENDING indicates
* that the header was not received completely.
*/
static int
hybiReadHeader(ws_ctx_t *wsctx, int *sockRet, int *nPayload)
{
int ret;
char *headerDst = wsctx->codeBufDecode + wsctx->header.nRead;
int n = ((uint64_t)WSHLENMAX) - wsctx->header.nRead;
ws_dbg("header_read to %p with len=%d\n", headerDst, n);
ret = wsctx->ctxInfo.readFunc(wsctx->ctxInfo.ctxPtr, headerDst, n);
ws_dbg("read %d bytes from socket\n", ret);
if (ret <= 0) {
if (-1 == ret) {
/* save errno because rfbErr() will tamper it */
int olderrno = errno;
rfbErr("%s: read; %s\n", __func__, strerror(errno));
errno = olderrno;
goto err_cleanup_state;
} else {
*sockRet = 0;
goto err_cleanup_state_sock_closed;
}
}
wsctx->header.nRead += ret;
if (wsctx->header.nRead < 2) {
/* cannot decode header with less than two bytes */
goto ret_header_pending;
}
/* first two header bytes received; interpret header data and get rest */
wsctx->header.data = (ws_header_t *)wsctx->codeBufDecode;
wsctx->header.opcode = wsctx->header.data->b0 & 0x0f;
wsctx->header.fin = (wsctx->header.data->b0 & 0x80) >> 7;
if (isControlFrame(wsctx)) {
ws_dbg("is control frame\n");
/* is a control frame, leave remembered continuation opcode unchanged;
* just check if there is a wrong fragmentation */
if (wsctx->header.fin == 0) {
/* we only accept text/binary continuation frames; RFC6455:
* Control frames (see Section 5.5) MAY be injected in the middle of
* a fragmented message. Control frames themselves MUST NOT be
* fragmented. */
rfbErr("control frame with FIN bit cleared received, aborting\n");
errno = EPROTO;
goto err_cleanup_state;
}
} else {
ws_dbg("not a control frame\n");
/* not a control frame, check for continuation opcode */
if (wsctx->header.opcode == WS_OPCODE_CONTINUATION) {
ws_dbg("cont_frame\n");
/* do we have state (i.e., opcode) for continuation frame? */
if (wsctx->continuation_opcode == WS_OPCODE_INVALID) {
rfbErr("no continuation state\n");
errno = EPROTO;
goto err_cleanup_state;
}
/* otherwise, set opcode = continuation_opcode */
wsctx->header.opcode = wsctx->continuation_opcode;
ws_dbg("set opcode to continuation_opcode: %d\n", wsctx->header.opcode);
} else {
if (wsctx->header.fin == 0) {
wsctx->continuation_opcode = wsctx->header.opcode;
} else {
wsctx->continuation_opcode = WS_OPCODE_INVALID;
}
ws_dbg("set continuation_opcode to %d\n", wsctx->continuation_opcode);
}
}
wsctx->header.payloadLen = (uint64_t)(wsctx->header.data->b1 & 0x7f);
ws_dbg("first header bytes received; opcode=%d lenbyte=%d fin=%d\n", wsctx->header.opcode, wsctx->header.payloadLen, wsctx->header.fin);
/*
* 4.3. Client-to-Server Masking
*
* The client MUST mask all frames sent to the server. A server MUST
* close the connection upon receiving a frame with the MASK bit set to 0.
**/
if (!(wsctx->header.data->b1 & 0x80)) {
rfbErr("%s: got frame without mask; ret=%d\n", __func__, ret);
errno = EPROTO;
goto err_cleanup_state;
}
if (wsctx->header.payloadLen < 126 && wsctx->header.nRead >= 6) {
wsctx->header.headerLen = WS_HYBI_HEADER_LEN_SHORT;
wsctx->header.mask = wsctx->header.data->u.m;
} else if (wsctx->header.payloadLen == 126 && 8 <= wsctx->header.nRead) {
wsctx->header.headerLen = WS_HYBI_HEADER_LEN_EXTENDED;
wsctx->header.payloadLen = WS_NTOH16(wsctx->header.data->u.s16.l16);
wsctx->header.mask = wsctx->header.data->u.s16.m16;
} else if (wsctx->header.payloadLen == 127 && 14 <= wsctx->header.nRead) {
wsctx->header.headerLen = WS_HYBI_HEADER_LEN_LONG;
wsctx->header.payloadLen = WS_NTOH64(wsctx->header.data->u.s64.l64);
wsctx->header.mask = wsctx->header.data->u.s64.m64;
} else {
/* Incomplete frame header, try again */
rfbErr("%s: incomplete frame header; ret=%d\n", __func__, ret);
goto ret_header_pending;
}
char *h = wsctx->codeBufDecode;
int i;
ws_dbg("Header:\n");
for (i=0; i <10; i++) {
ws_dbg("0x%02X\n", (unsigned char)h[i]);
}
ws_dbg("\n");
/* while RFC 6455 mandates that lengths MUST be encoded with the minimum
* number of bytes, it does not specify for the server how to react on
* 'wrongly' encoded frames --- this implementation rejects them*/
if ((wsctx->header.headerLen > WS_HYBI_HEADER_LEN_SHORT
&& wsctx->header.payloadLen < (uint64_t)126)
|| (wsctx->header.headerLen > WS_HYBI_HEADER_LEN_EXTENDED
&& wsctx->header.payloadLen < (uint64_t)65536)) {
rfbErr("%s: invalid length field; headerLen=%d payloadLen=%llu\n", __func__, wsctx->header.headerLen, wsctx->header.payloadLen);
errno = EPROTO;
goto err_cleanup_state;
}
/* update write position for next bytes */
wsctx->writePos = wsctx->codeBufDecode + wsctx->header.nRead;
/* set payload pointer just after header */
wsctx->readPos = (unsigned char *)(wsctx->codeBufDecode + wsctx->header.headerLen);
*nPayload = wsctx->header.nRead - wsctx->header.headerLen;
wsctx->nReadPayload = *nPayload;
ws_dbg("header complete: state=%d headerlen=%d payloadlen=%llu writeTo=%p nPayload=%d\n", wsctx->hybiDecodeState, wsctx->header.headerLen, wsctx->header.payloadLen, wsctx->writePos, *nPayload);
return WS_HYBI_STATE_DATA_NEEDED;
ret_header_pending:
errno = EAGAIN;
*sockRet = -1;
return WS_HYBI_STATE_HEADER_PENDING;
err_cleanup_state:
*sockRet = -1;
err_cleanup_state_sock_closed:
hybiDecodeCleanupComplete(wsctx);
return WS_HYBI_STATE_ERR;
}
static int
hybiWsFrameComplete(ws_ctx_t *wsctx)
{
return wsctx != NULL && hybiRemaining(wsctx) == 0;
}
static char *
hybiPayloadStart(ws_ctx_t *wsctx)
{
return wsctx->codeBufDecode + wsctx->header.headerLen;
}
/**
* Read the remaining payload bytes from associated raw socket.
*
* - try to read remaining bytes from socket
* - unmask all multiples of 4
* - if frame incomplete but some bytes are left, these are copied to
* the carry buffer
* - if opcode is TEXT: Base64-decode all unmasked received bytes
* - set state for reading decoded data
* - reset write position to begin of buffer (+ header)
* --> before we retrieve more data we let the caller clear all bytes
* from the reception buffer
* - execute return data routine
*
* Sets errno corresponding to what it gets from the underlying
* socket or EPROTO if some invalid data is in the received frame
* or ECONNRESET if a close reason + message is received. EIO is used if
* an internal sanity check fails.
*
* @param[in] cl client ptr with raw socket reference
* @param[out] dst destination buffer
* @param[in] len size of destination buffer
* @param[out] sockRet emulated recv return value
* @param[in] nInBuf number of undecoded bytes before writePos from header read
* @return next hybi decode state
*/
static int
hybiReadAndDecode(ws_ctx_t *wsctx, char *dst, int len, int *sockRet, int nInBuf)
{
int n;
int i;
int toReturn; /* number of data bytes to return */
int toDecode; /* number of bytes to decode starting at wsctx->writePos */
int bufsize;
int nextRead;
unsigned char *data;
uint32_t *data32;
/* if data was carried over, copy to start of buffer */
memcpy(wsctx->writePos, wsctx->carryBuf, wsctx->carrylen);
wsctx->writePos += wsctx->carrylen;
/* -1 accounts for potential '\0' terminator for base64 decoding */
bufsize = wsctx->codeBufDecode + ARRAYSIZE(wsctx->codeBufDecode) - wsctx->writePos - 1;
ws_dbg("bufsize=%d\n", bufsize);
if (hybiRemaining(wsctx) > bufsize) {
nextRead = bufsize;
} else {
nextRead = hybiRemaining(wsctx);
}
ws_dbg("calling read with buf=%p and len=%d (decodebuf=%p headerLen=%d)\n", wsctx->writePos, nextRead, wsctx->codeBufDecode, wsctx->header.headerLen);
if (nextRead > 0) {
/* decode more data */
if (-1 == (n = wsctx->ctxInfo.readFunc(wsctx->ctxInfo.ctxPtr, wsctx->writePos, nextRead))) {
int olderrno = errno;
rfbErr("%s: read; %s", __func__, strerror(errno));
errno = olderrno;
*sockRet = -1;
return WS_HYBI_STATE_ERR;
} else if (n == 0) {
*sockRet = 0;
return WS_HYBI_STATE_ERR;
} else {
ws_dbg("read %d bytes from socket; nRead=%d\n", n, wsctx->nReadPayload);
}
} else {
n = 0;
}
wsctx->nReadPayload += n;
wsctx->writePos += n;
if (hybiRemaining(wsctx) == 0) {
wsctx->hybiDecodeState = WS_HYBI_STATE_FRAME_COMPLETE;
}
/* number of not yet unmasked payload bytes: what we read here + what was
* carried over + what was read with the header */
toDecode = n + wsctx->carrylen + nInBuf;
ws_dbg("toDecode=%d from n=%d carrylen=%d headerLen=%d\n", toDecode, n, wsctx->carrylen, wsctx->header.headerLen);
if (toDecode < 0) {
rfbErr("%s: internal error; negative number of bytes to decode: %d", __func__, toDecode);
errno=EIO;
*sockRet = -1;
return WS_HYBI_STATE_ERR;
}
/* for a possible base64 decoding, we decode multiples of 4 bytes until
* the whole frame is received and carry over any remaining bytes in the carry buf*/
data = (unsigned char *)(wsctx->writePos - toDecode);
data32= (uint32_t *)data;
for (i = 0; i < (toDecode >> 2); i++) {
data32[i] ^= wsctx->header.mask.u;
}
ws_dbg("mask decoding; i=%d toDecode=%d\n", i, toDecode);
if (wsctx->hybiDecodeState == WS_HYBI_STATE_FRAME_COMPLETE) {
/* process the remaining bytes (if any) */
for (i*=4; i < toDecode; i++) {
data[i] ^= wsctx->header.mask.c[i % 4];
}
/* all data is here, no carrying */
wsctx->carrylen = 0;
} else {
/* carry over remaining, non-multiple-of-four bytes */
wsctx->carrylen = toDecode - (i * 4);
if (wsctx->carrylen < 0 || wsctx->carrylen > ARRAYSIZE(wsctx->carryBuf)) {
rfbErr("%s: internal error, invalid carry over size: carrylen=%d, toDecode=%d, i=%d", __func__, wsctx->carrylen, toDecode, i);
*sockRet = -1;
errno = EIO;
return WS_HYBI_STATE_ERR;
}
ws_dbg("carrying over %d bytes from %p to %p\n", wsctx->carrylen, wsctx->writePos + (i * 4), wsctx->carryBuf);
memcpy(wsctx->carryBuf, data + (i * 4), wsctx->carrylen);
wsctx->writePos -= wsctx->carrylen;
}
toReturn = toDecode - wsctx->carrylen;
switch (wsctx->header.opcode) {
case WS_OPCODE_CLOSE:
/* this data is not returned as payload data */
if (hybiWsFrameComplete(wsctx)) {
*(wsctx->writePos) = '\0';
ws_dbg("got close cmd %d, reason %d: %s\n", (int)(wsctx->writePos - hybiPayloadStart(wsctx)), WS_NTOH16(((uint16_t *)hybiPayloadStart(wsctx))[0]), &hybiPayloadStart(wsctx)[2]);
errno = ECONNRESET;
*sockRet = -1;
return WS_HYBI_STATE_FRAME_COMPLETE;
} else {
ws_dbg("got close cmd; waiting for %d more bytes to arrive\n", hybiRemaining(wsctx));
*sockRet = -1;
errno = EAGAIN;
return WS_HYBI_STATE_CLOSE_REASON_PENDING;
}
break;
case WS_OPCODE_TEXT_FRAME:
data[toReturn] = '\0';
ws_dbg("Initiate Base64 decoding in %p with max size %d and '\\0' at %p\n", data, bufsize, data + toReturn);
if (-1 == (wsctx->readlen = rfbBase64PtoN((char *)data, data, bufsize))) {
rfbErr("%s: Base64 decode error; %s\n", __func__, strerror(errno));
}
wsctx->writePos = hybiPayloadStart(wsctx);
break;
case WS_OPCODE_BINARY_FRAME:
wsctx->readlen = toReturn;
wsctx->writePos = hybiPayloadStart(wsctx);
ws_dbg("set readlen=%d writePos=%p\n", wsctx->readlen, wsctx->writePos);
break;
default:
rfbErr("%s: unhandled opcode %d, b0: %02x, b1: %02x\n", __func__, (int)wsctx->header.opcode, wsctx->header.data->b0, wsctx->header.data->b1);
}
wsctx->readPos = data;
return hybiReturnData(dst, len, wsctx, sockRet);
}
/**
* Read function for websocket-socket emulation.
*
* 0 1 2 3
* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
* +-+-+-+-+-------+-+-------------+-------------------------------+
* |F|R|R|R| opcode|M| Payload len | Extended payload length |
* |I|S|S|S| (4) |A| (7) | (16/64) |
* |N|V|V|V| |S| | (if payload len==126/127) |
* | |1|2|3| |K| | |
* +-+-+-+-+-------+-+-------------+ - - - - - - - - - - - - - - - +
* | Extended payload length continued, if payload len == 127 |
* + - - - - - - - - - - - - - - - +-------------------------------+
* | |Masking-key, if MASK set to 1 |
* +-------------------------------+-------------------------------+
* | Masking-key (continued) | Payload Data |
* +-------------------------------- - - - - - - - - - - - - - - - +
* : Payload Data continued ... :
* + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - +
* | Payload Data continued ... |
* +---------------------------------------------------------------+
*
* Using the decode buffer, this function:
* - reads the complete header from the underlying socket
* - reads any remaining data bytes
* - unmasks the payload data using the provided mask
* - decodes Base64 encoded text data
* - copies len bytes of decoded payload data into dst
*
* Emulates a read call on a socket.
*/
int
webSocketsDecodeHybi(ws_ctx_t *wsctx, char *dst, int len)
{
int result = -1;
/* int fin; */ /* not used atm */
ws_dbg("%s_enter: len=%d; "
"CTX: readlen=%d readPos=%p "
"writeTo=%p "
"state=%d payloadtoRead=%d payloadRemaining=%llu "
" nReadPayload=%d carrylen=%d carryBuf=%p\n",
__func__, len,
wsctx->readlen, wsctx->readPos,
wsctx->writePos,
wsctx->hybiDecodeState, wsctx->header.payloadLen, hybiRemaining(wsctx),
wsctx->nReadPayload, wsctx->carrylen, wsctx->carryBuf);
switch (wsctx->hybiDecodeState){
int nInBuf;
case WS_HYBI_STATE_HEADER_PENDING:
wsctx->hybiDecodeState = hybiReadHeader(wsctx, &result, &nInBuf);
if (wsctx->hybiDecodeState == WS_HYBI_STATE_ERR) {
goto spor;
}
if (wsctx->hybiDecodeState != WS_HYBI_STATE_HEADER_PENDING) {
/* when header is complete, try to read some more data */
wsctx->hybiDecodeState = hybiReadAndDecode(wsctx, dst, len, &result, nInBuf);
}
break;
case WS_HYBI_STATE_DATA_AVAILABLE:
wsctx->hybiDecodeState = hybiReturnData(dst, len, wsctx, &result);
break;
case WS_HYBI_STATE_DATA_NEEDED:
wsctx->hybiDecodeState = hybiReadAndDecode(wsctx, dst, len, &result, 0);
break;
case WS_HYBI_STATE_CLOSE_REASON_PENDING:
wsctx->hybiDecodeState = hybiReadAndDecode(wsctx, dst, len, &result, 0);
break;
default:
/* invalid state */
rfbErr("%s: called with invalid state %d\n", wsctx->hybiDecodeState);
result = -1;
errno = EIO;
wsctx->hybiDecodeState = WS_HYBI_STATE_ERR;
}
/* single point of return, if someone has questions :-) */
spor:
if (wsctx->hybiDecodeState == WS_HYBI_STATE_FRAME_COMPLETE) {
ws_dbg("frame received successfully, cleaning up: read=%d hlen=%d plen=%d\n", wsctx->header.nRead, wsctx->header.headerLen, wsctx->header.payloadLen);
if (wsctx->header.fin && !isControlFrame(wsctx)) {
/* frame finished, cleanup state */
hybiDecodeCleanupComplete(wsctx);
} else {
/* always retain continuation opcode for unfinished data frames
* or control frames, which may interleave with data frames */
hybiDecodeCleanupForContinuation(wsctx);
}
} else if (wsctx->hybiDecodeState == WS_HYBI_STATE_ERR) {
hybiDecodeCleanupComplete(wsctx);
}
ws_dbg("%s_exit: len=%d; "
"CTX: readlen=%d readPos=%p "
"writePos=%p "
"state=%d payloadtoRead=%d payloadRemaining=%d "
"nRead=%d carrylen=%d carryBuf=%p "
"result=%d "
"errno=%d\n",
__func__, len,
wsctx->readlen, wsctx->readPos,
wsctx->writePos,
wsctx->hybiDecodeState, wsctx->header.payloadLen, hybiRemaining(wsctx),
wsctx->nReadPayload, wsctx->carrylen, wsctx->carryBuf,
result,
errno);
return result;
}
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