commit 81706d84279f0a2870f8b1789403188fd933b32a Author: David Goulet dgoulet@torproject.org Date: Wed Jan 9 14:03:32 2019 -0500
prop289: Support SENDME v1 cell parsing
This commit makes tor able to parse and handle a SENDME version 1. It will look at the consensus parameter "sendme_accept_min_version" to know what is the minimum version it should look at.
IMPORTANT: At this commit, the validation of the cell is not fully implemented. For this, we need #26839 to be completed that is to match the SENDME digest with the last cell digest.
Closes #26841
Signed-off-by: David Goulet dgoulet@torproject.org --- src/core/or/relay.c | 4 +- src/core/or/sendme.c | 140 +++++++++++++++++++++++++++++++++++++++++++++++++-- src/core/or/sendme.h | 3 +- 3 files changed, 140 insertions(+), 7 deletions(-)
diff --git a/src/core/or/relay.c b/src/core/or/relay.c index 6f69ed999..76f2203a9 100644 --- a/src/core/or/relay.c +++ b/src/core/or/relay.c @@ -1814,7 +1814,9 @@ connection_edge_process_relay_cell(cell_t *cell, circuit_t *circ,
if (!rh.stream_id) { /* Circuit level SENDME cell. */ - ret = sendme_process_circuit_level(layer_hint, circ, rh.length); + ret = sendme_process_circuit_level(layer_hint, circ, + cell->payload + RELAY_HEADER_SIZE, + rh.length); if (ret < 0) { return ret; } diff --git a/src/core/or/sendme.c b/src/core/or/sendme.c index f22e7027d..64497055e 100644 --- a/src/core/or/sendme.c +++ b/src/core/or/sendme.c @@ -18,6 +18,10 @@ #include "feature/nodelist/networkstatus.h" #include "trunnel/sendme.h"
+/* The maximum supported version. Above that value, the cell can't be + * recognized as a valid SENDME. */ +#define SENDME_MAX_SUPPORTED_VERSION 1 + /* The cell version constants for when emitting a cell. */ #define SENDME_EMIT_MIN_VERSION_DEFAULT 0 #define SENDME_EMIT_MIN_VERSION_MIN 0 @@ -39,7 +43,6 @@ get_emit_min_version(void) SENDME_EMIT_MIN_VERSION_MAX); }
-#if 0 /* Return the minimum version given by the consensus (if any) that should be * accepted when receiving a SENDME cell. */ static int @@ -50,7 +53,124 @@ get_accept_min_version(void) SENDME_ACCEPT_MIN_VERSION_MIN, SENDME_ACCEPT_MIN_VERSION_MAX); } -#endif + +/* Return true iff the given decoded SENDME version 1 cell is valid. + * + * Validation is done by comparing the digest in the cell from the previous + * cell we saw which tells us that the other side has in fact seen that cell. + * See proposal 289 for more details. */ +static bool +cell_v1_is_valid(const sendme_cell_t *cell) +{ + sendme_data_v1_t *data = NULL; + + tor_assert(cell); + + if (sendme_data_v1_parse(&data, sendme_cell_getconstarray_data(cell), + sendme_cell_getlen_data(cell)) < 0) { + goto invalid; + } + + /* XXX: Match the digest in the cell to the previous cell. Needs to be + * implemented that is passed to this function and compared. For this, we + * need #26839 that is making tor remember the last digest(s). */ + + /* Validated SENDME v1 cell. */ + sendme_data_v1_free(data); + return 1; + invalid: + sendme_data_v1_free(data); + return 0; +} + +/* Return true iff the given cell version can be handled or if the minimum + * accepted version from the consensus is known to us. */ +static bool +cell_version_is_valid(uint8_t cell_version) +{ + int accept_version = get_accept_min_version(); + + /* Can we handle this version? */ + if (accept_version > SENDME_MAX_SUPPORTED_VERSION) { + log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL, + "Unable to handle SENDME version %u. We only support <= %d " + "(from consensus). Probably your tor is too old?", + accept_version, cell_version); + goto invalid; + } + + /* We only accept a SENDME cell from what the consensus tells us. */ + if (cell_version < accept_version) { + log_info(LD_PROTOCOL, "Unacceptable SENDME version %d. Only " + "accepting %u (taken from the consensus). " + "Closing circuit.", + cell_version, accept_version); + goto invalid; + } + + return 1; + invalid: + return 0; +} + +/* Return true iff the encoded SENDME cell in cell_payload of length + * cell_payload_len is valid. For each version: + * + * 0: No validation + * 1: Authenticated with last cell digest. + * + * This is the main critical function to make sure we can continue to + * send/recv cells on a circuit. If the SENDME is invalid, the circuit should + * be mark for close. */ +static bool +sendme_is_valid(const uint8_t *cell_payload, size_t cell_payload_len) +{ + uint8_t cell_version; + sendme_cell_t *cell = NULL; + + tor_assert(cell_payload); + + /* An empty payload means version 0 so skip trunnel parsing. We won't be + * able to parse a 0 length buffer into a valid SENDME cell. */ + if (cell_payload_len == 0) { + cell_version = 0; + } else { + /* First we'll decode the cell so we can get the version. */ + if (sendme_cell_parse(&cell, cell_payload, cell_payload_len) < 0) { + log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL, + "Unparseable SENDME cell received. Closing circuit."); + goto invalid; + } + cell_version = sendme_cell_get_version(cell); + } + + /* Validate that we can handle this cell version. */ + if (!cell_version_is_valid(cell_version)) { + goto invalid; + } + + /* Validate depending on the version now. */ + switch (cell_version) { + case 0x01: + if (!cell_v1_is_valid(cell)) { + goto invalid; + } + break; + case 0x00: + /* Fallthrough. Version 0, there is no work to be done on the payload so + * it is necessarily valid if we pass the version validation. */ + default: + /* Unknown version means we can't handle it so fallback to version 0. */ + break; + } + + /* Valid cell. */ + sendme_cell_free(cell); + return 1; + invalid: + sendme_cell_free(cell); + return 0; +}
/* Build and encode a version 1 SENDME cell into payload, which must be at * least of RELAY_PAYLOAD_SIZE bytes, using the digest for the cell data. @@ -215,7 +335,8 @@ sendme_circuit_consider_sending(circuit_t *circ, crypt_path_t *layer_hint, /* Process a circuit-level SENDME cell that we just received. The layer_hint, * if not NULL, is the Exit hop of the connection which means that we are a * client. In that case, circ must be an origin circuit. The cell_body_len is - * the length of the SENDME cell payload (excluding the header). + * the length of the SENDME cell payload (excluding the header). The + * cell_payload is the payload. * * Return 0 on success that is the SENDME is valid and the package window has * been updated properly. @@ -224,9 +345,11 @@ sendme_circuit_consider_sending(circuit_t *circ, crypt_path_t *layer_hint, * be closed using the value as the reason for it. */ int sendme_process_circuit_level(crypt_path_t *layer_hint, - circuit_t *circ, uint16_t cell_body_len) + circuit_t *circ, const uint8_t *cell_payload, + uint16_t cell_payload_len) { tor_assert(circ); + tor_assert(cell_payload);
/* If we are the origin of the circuit, we are the Client so we use the * layer hint (the Exit hop) for the package window tracking. */ @@ -245,8 +368,15 @@ sendme_process_circuit_level(crypt_path_t *layer_hint,
/* We count circuit-level sendme's as valid delivered data because they * are rate limited. */ - circuit_read_valid_data(TO_ORIGIN_CIRCUIT(circ), cell_body_len); + circuit_read_valid_data(TO_ORIGIN_CIRCUIT(circ), cell_payload_len); } else { + /* Validate the SENDME cell. Depending on the version, different + * validation can be done. An invalid SENDME requires us to close the + * circuit. It is only done if we are the Exit of the circuit. */ + if (!sendme_is_valid(cell_payload, cell_payload_len)) { + return -END_CIRC_REASON_TORPROTOCOL; + } + /* We aren't the origin of this circuit so we are the Exit and thus we * track the package window with the circuit object. */ if ((circ->package_window + CIRCWINDOW_INCREMENT) > diff --git a/src/core/or/sendme.h b/src/core/or/sendme.h index ba01ecfaf..033bc6ff7 100644 --- a/src/core/or/sendme.h +++ b/src/core/or/sendme.h @@ -21,7 +21,8 @@ void sendme_circuit_consider_sending(circuit_t *circ,
/* Processing SENDME cell. */ int sendme_process_circuit_level(crypt_path_t *layer_hint, - circuit_t *circ, uint16_t cell_body_len); + circuit_t *circ, const uint8_t *cell_payload, + uint16_t cell_payload_len); int sendme_process_stream_level(edge_connection_t *conn, circuit_t *circ, uint16_t cell_body_len);