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https://gitlab.torproject.org/tpo/core/tor.git
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87 lines
2.8 KiB
C
87 lines
2.8 KiB
C
/* Copyright (c) 2001 Matej Pfajfar.
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* Copyright (c) 2001-2004, Roger Dingledine.
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* Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
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* Copyright (c) 2007-2018, The Tor Project, Inc. */
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/* See LICENSE for licensing information */
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#include "or.h"
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#include "buffers.h"
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#include "proto_cell.h"
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#include "connection_or.h"
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#include "var_cell_st.h"
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/** True iff the cell command <b>command</b> is one that implies a
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* variable-length cell in Tor link protocol <b>linkproto</b>. */
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static inline int
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cell_command_is_var_length(uint8_t command, int linkproto)
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{
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/* If linkproto is v2 (2), CELL_VERSIONS is the only variable-length cells
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* work as implemented here. If it's 1, there are no variable-length cells.
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* Tor does not support other versions right now, and so can't negotiate
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* them.
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*/
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switch (linkproto) {
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case 1:
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/* Link protocol version 1 has no variable-length cells. */
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return 0;
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case 2:
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/* In link protocol version 2, VERSIONS is the only variable-length cell */
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return command == CELL_VERSIONS;
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case 0:
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case 3:
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default:
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/* In link protocol version 3 and later, and in version "unknown",
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* commands 128 and higher indicate variable-length. VERSIONS is
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* grandfathered in. */
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return command == CELL_VERSIONS || command >= 128;
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}
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}
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/** Check <b>buf</b> for a variable-length cell according to the rules of link
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* protocol version <b>linkproto</b>. If one is found, pull it off the buffer
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* and assign a newly allocated var_cell_t to *<b>out</b>, and return 1.
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* Return 0 if whatever is on the start of buf_t is not a variable-length
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* cell. Return 1 and set *<b>out</b> to NULL if there seems to be the start
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* of a variable-length cell on <b>buf</b>, but the whole thing isn't there
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* yet. */
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int
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fetch_var_cell_from_buf(buf_t *buf, var_cell_t **out, int linkproto)
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{
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char hdr[VAR_CELL_MAX_HEADER_SIZE];
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var_cell_t *result;
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uint8_t command;
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uint16_t length;
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const int wide_circ_ids = linkproto >= MIN_LINK_PROTO_FOR_WIDE_CIRC_IDS;
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const int circ_id_len = get_circ_id_size(wide_circ_ids);
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const unsigned header_len = get_var_cell_header_size(wide_circ_ids);
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*out = NULL;
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if (buf_datalen(buf) < header_len)
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return 0;
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buf_peek(buf, hdr, header_len);
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command = get_uint8(hdr + circ_id_len);
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if (!(cell_command_is_var_length(command, linkproto)))
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return 0;
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length = ntohs(get_uint16(hdr + circ_id_len + 1));
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if (buf_datalen(buf) < (size_t)(header_len+length))
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return 1;
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result = var_cell_new(length);
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result->command = command;
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if (wide_circ_ids)
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result->circ_id = ntohl(get_uint32(hdr));
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else
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result->circ_id = ntohs(get_uint16(hdr));
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buf_drain(buf, header_len);
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buf_peek(buf, (char*) result->payload, length);
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buf_drain(buf, length);
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*out = result;
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return 1;
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}
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