Introduce new guard restriction and use it to skip outdated dirs. (f61e3090) · Commits · Mike Perry / Tor

changes/bug23817

0 → 100644

+3 −0

Original line number	Diff line number	Diff line
		o Minor bugfixes (descriptors):
		- Don't try fetching microdescriptors from relays that have failed to
		deliver them in the past. Fixes bug 23817; bugfix on 0.3.0.1-alpha.

src/or/directory.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -464,7 +464,7 @@ directory_pick_generic_dirserver(dirinfo_type_t type, int pds_flags,
		log_warn(LD_BUG, "Called when we have UseBridges set.");

		if (should_use_directory_guards(options)) {
		const node_t *node = guards_choose_dirguard(guard_state_out);
		const node_t *node = guards_choose_dirguard(dir_purpose, guard_state_out);
		if (node)
		rs = node->rs;
		} else {
		@@ -598,7 +598,7 @@ directory_get_from_dirserver,(
		* sort of dir fetch we'll be doing, so it won't return a bridge
		* that can't answer our question.
		*/
		const node_t *node = guards_choose_dirguard(&guard_state);
		const node_t *node = guards_choose_dirguard(dir_purpose, &guard_state);
		if (node && node->ri) {
		/* every bridge has a routerinfo. */
		routerinfo_t *ri = node->ri;

src/or/entrynodes.c

+84 −11

Original line number	Diff line number	Diff line
		@@ -1460,6 +1460,70 @@ guard_in_node_family(const entry_guard_t guard, const node_t node)
		}
		}

		/* Allocate and return a new exit guard restriction (where <b>exit_id</b> is of
		* size DIGEST_LEN) */
		STATIC entry_guard_restriction_t *
		guard_create_exit_restriction(const uint8_t *exit_id)
		{
		entry_guard_restriction_t *rst = NULL;
		rst = tor_malloc_zero(sizeof(entry_guard_restriction_t));
		rst->type = RST_EXIT_NODE;
		memcpy(rst->exclude_id, exit_id, DIGEST_LEN);
		return rst;
		}

		/** Allocate and return an outdated md guard restriction. */
		STATIC entry_guard_restriction_t *
		guard_create_dirserver_md_restriction(void)
		{
		entry_guard_restriction_t *rst = NULL;

		rst = tor_malloc_zero(sizeof(entry_guard_restriction_t));
		rst->type = RST_OUTDATED_MD_DIRSERVER;

		return rst;
		}

		/* Return True if <b>guard</b> obeys the exit restriction <b>rst</b>. */
		static int
		guard_obeys_exit_restriction(const entry_guard_t *guard,
		const entry_guard_restriction_t *rst)
		{
		tor_assert(rst->type == RST_EXIT_NODE);

		// Exclude the exit ID and all of its family.
		const node_t node = node_get_by_id((const char)rst->exclude_id);
		if (node && guard_in_node_family(guard, node))
		return 0;

		return tor_memneq(guard->identity, rst->exclude_id, DIGEST_LEN);
		}

		/** Return True if <b>guard</b> should be used as a dirserver for fetching
		* microdescriptors. */
		static int
		guard_obeys_md_dirserver_restriction(const entry_guard_t *guard)
		{
		/* Don't enforce dirserver restrictions for bridges since we might not have
		* many of those. Be willing to try them over and over again for now. */
		/* XXX: Improvement might be possible here */
		if (guard->bridge_addr) {
		return 1;
		}

		/* If this guard is an outdated dirserver, don't use it. */
		if (microdesc_relay_is_outdated_dirserver(guard->identity)) {
		log_info(LD_GENERAL, "Skipping %s dirserver: outdated",
		hex_str(guard->identity, DIGEST_LEN));
		return 0;
		}

		log_debug(LD_GENERAL, "%s dirserver obeys md restrictions",
		hex_str(guard->identity, DIGEST_LEN));

		return 1;
		}

		/**
		* Return true iff <b>guard</b> obeys the restrictions defined in <b>rst</b>.
		* (If <b>rst</b> is NULL, there are no restrictions.)
		@@ -1472,13 +1536,14 @@ entry_guard_obeys_restriction(const entry_guard_t *guard,
		if (! rst)
		return 1; // No restriction? No problem.

		// Only one kind of restriction exists right now: excluding an exit
		// ID and all of its family.
		const node_t node = node_get_by_id((const char)rst->exclude_id);
		if (node && guard_in_node_family(guard, node))
		return 0;
		if (rst->type == RST_EXIT_NODE) {
		return guard_obeys_exit_restriction(guard, rst);
		} else if (rst->type == RST_OUTDATED_MD_DIRSERVER) {
		return guard_obeys_md_dirserver_restriction(guard);
		}

		return tor_memneq(guard->identity, rst->exclude_id, DIGEST_LEN);
		tor_assert_nonfatal_unreached();
		return 0;
		}

		/**
		@@ -2105,7 +2170,7 @@ entry_guard_has_higher_priority(entry_guard_t a, entry_guard_t b)
		}

		/** Release all storage held in <b>restriction</b> */
		static void
		STATIC void
		entry_guard_restriction_free(entry_guard_restriction_t *rst)
		{
		tor_free(rst);
		@@ -3358,8 +3423,8 @@ guards_choose_guard(cpath_build_state_t *state,
		/* We're building to a targeted exit node, so that node can't be
		* chosen as our guard for this circuit. Remember that fact in a
		* restriction. */
		rst = tor_malloc_zero(sizeof(entry_guard_restriction_t));
		memcpy(rst->exclude_id, exit_id, DIGEST_LEN);
		rst = guard_create_exit_restriction(exit_id);
		tor_assert(rst);
		}
		if (entry_guard_pick_for_circuit(get_guard_selection_info(),
		GUARD_USAGE_TRAFFIC,
		@@ -3411,12 +3476,20 @@ remove_all_entry_guards(void)

		/** Helper: pick a directory guard, with whatever algorithm is used. */
		const node_t *
		guards_choose_dirguard(circuit_guard_state_t **guard_state_out)
		guards_choose_dirguard(uint8_t dir_purpose,
		circuit_guard_state_t **guard_state_out)
		{
		const node_t *r = NULL;
		entry_guard_restriction_t *rst = NULL;

		/* If we are fetching microdescs, don't query outdated dirservers. */
		if (dir_purpose == DIR_PURPOSE_FETCH_MICRODESC) {
		rst = guard_create_dirserver_md_restriction();
		}

		if (entry_guard_pick_for_circuit(get_guard_selection_info(),
		GUARD_USAGE_DIRGUARD,
		NULL,
		rst,
		&r,
		guard_state_out) < 0) {
		tor_assert(r == NULL);

src/or/entrynodes.h

+27 −10

Original line number	Diff line number	Diff line
		@@ -272,22 +272,28 @@ struct guard_selection_s {

		struct entry_guard_handle_t;

		/** Types of restrictions we impose when picking guard nodes */
		typedef enum guard_restriction_type_t {
		/* Don't pick the same guard node as our exit node (or its family) */
		RST_EXIT_NODE = 0,
		/* Don't pick dirguards that have previously shown to be outdated */
		RST_OUTDATED_MD_DIRSERVER = 1
		} guard_restriction_type_t;

		/**
		* A restriction to remember which entry guards are off-limits for a given
		* circuit.
		*
		* Right now, we only use restrictions to block a single guard and its family
		* from being selected; this mechanism is designed to be more extensible in
		* the future, however.
		*
		* Note: This mechanism is NOT for recording which guards are never to be
		* used: only which guards cannot be used on <em>one particular circuit</em>.
		*/
		struct entry_guard_restriction_t {
		/**
		* The guard's RSA identity digest must not equal this; and it must not
		* be in the same family as any node with this digest.
		*/
		/* What type of restriction are we imposing? */
		guard_restriction_type_t type;

		/* In case of restriction type RST_EXIT_NODE, the guard's RSA identity
		* digest must not equal this; and it must not be in the same family as any
		* node with this digest. */
		uint8_t exclude_id[DIGEST_LEN];
		};

		@@ -316,7 +322,8 @@ struct circuit_guard_state_t {
		int guards_update_all(void);
		const node_t guards_choose_guard(cpath_build_state_t state,
		circuit_guard_state_t **guard_state_out);
		const node_t guards_choose_dirguard(circuit_guard_state_t *guard_state_out);
		const node_t *guards_choose_dirguard(uint8_t dir_purpose,
		circuit_guard_state_t **guard_state_out);

		#if 1
		/* XXXX NM I would prefer that all of this stuff be private to
		@@ -550,7 +557,17 @@ STATIC unsigned entry_guards_note_guard_success(guard_selection_t *gs,
		unsigned old_state);
		STATIC int entry_guard_has_higher_priority(entry_guard_t a, entry_guard_t b);
		STATIC char getinfo_helper_format_single_entry_guard(const entry_guard_t e);
		#endif

		STATIC entry_guard_restriction_t *
		guard_create_exit_restriction(const uint8_t *exit_id);

		STATIC entry_guard_restriction_t *
		guard_create_dirserver_md_restriction(void);

		STATIC void
		entry_guard_restriction_free(entry_guard_restriction_t *rst);

		#endif /* defined(ENTRYNODES_PRIVATE) */

		void remove_all_entry_guards_for_guard_selection(guard_selection_t *gs);
		void remove_all_entry_guards(void);