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Bootstrap: check the exit policy and flag on descriptors

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Previously, Tor would only check the exit flag. In small networks, Tor
could bootstrap once it received a consensus with exits, without fetching
the new descriptors for those exits.

After bootstrap, Tor delays descriptor fetches, leading to failures in
fast networks like chutney.

Fixes 27236; bugfix on 0.2.6.3-alpha.
This commit is contained in:
teor
2018-08-24 00:10:52 +10:00
parent 573b6e4f2f
commit fadcab920b
2 changed files with 46 additions and 39 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/or/nodelist.c
+41 -39
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@@ -76,10 +76,17 @@ static void node_free_(node_t *node);
/** count_usable_descriptors counts descriptors with these flag(s)
*/
typedef enum {
/* All descriptors regardless of flags */
USABLE_DESCRIPTOR_ALL = 0,
/* Only descriptors with the Exit flag */
USABLE_DESCRIPTOR_EXIT_ONLY = 1
/* All descriptors regardless of flags or exit policies */
USABLE_DESCRIPTOR_ALL = 0U,
/* Only count descriptors with an exit policy that allows at least one port
*/
USABLE_DESCRIPTOR_EXIT_POLICY = 1U << 0,
/* Only count descriptors for relays that have the exit flag in the
* consensus */
USABLE_DESCRIPTOR_EXIT_FLAG = 1U << 1,
/* Only count descriptors for relays that have the policy and the flag */
USABLE_DESCRIPTOR_EXIT_POLICY_AND_FLAG = (USABLE_DESCRIPTOR_EXIT_POLICY |
USABLE_DESCRIPTOR_EXIT_FLAG)
} usable_descriptor_t;
static void count_usable_descriptors(int *num_present,
int *num_usable,
@@ -2110,8 +2117,11 @@ get_dir_info_status_string(void)
* *<b>num_present</b>).
*
* If <b>in_set</b> is non-NULL, only consider those routers in <b>in_set</b>.
* If <b>exit_only</b> is USABLE_DESCRIPTOR_EXIT_ONLY, only consider nodes
* with the Exit flag.
* If <b>exit_only</b> & USABLE_DESCRIPTOR_EXIT_POLICY, only consider nodes
* with an exit policy that accepts at least one port.
* If <b>exit_only</b> & USABLE_DESCRIPTOR_EXIT_FLAG, only consider nodes
* with the exit flag in the consensus.
*
* If *<b>descs_out</b> is present, add a node_t for each usable descriptor
* to it.
*/
@@ -2132,11 +2142,17 @@ count_usable_descriptors(int *num_present, int *num_usable,
if (!node)
continue; /* This would be a bug: every entry in the consensus is
* supposed to have a node. */
if (exit_only == USABLE_DESCRIPTOR_EXIT_ONLY && ! rs->is_exit)
if ((exit_only & USABLE_DESCRIPTOR_EXIT_FLAG) && ! rs->is_exit)
continue;
if (in_set && ! routerset_contains_routerstatus(in_set, rs, -1))
continue;
if (client_would_use_router(rs, now)) {
/* Do the policy check last, because it's potentially expensive */
if ((exit_only & USABLE_DESCRIPTOR_EXIT_POLICY) &&
node_has_preferred_descriptor(node, 0) &&
node_exit_policy_rejects_all(node)) {
continue;
}
const char * const digest = rs->descriptor_digest;
int present;
++*num_usable; /* the consensus says we want it. */
@@ -2154,10 +2170,17 @@ count_usable_descriptors(int *num_present, int *num_usable,
}
SMARTLIST_FOREACH_END(rs);
log_debug(LD_DIR, "%d usable, %d present (%s%s).",
log_debug(LD_DIR, "%d usable, %d present (%s%s%s%s%s).",
*num_usable, *num_present,
md ? "microdesc" : "desc",
exit_only == USABLE_DESCRIPTOR_EXIT_ONLY ? " exits" : "s");
(exit_only & USABLE_DESCRIPTOR_EXIT_POLICY_AND_FLAG) ?
" exit" : "s",
(exit_only & USABLE_DESCRIPTOR_EXIT_POLICY) ?
" policies" : "" ,
(exit_only == USABLE_DESCRIPTOR_EXIT_POLICY_AND_FLAG) ?
" and" : "" ,
(exit_only & USABLE_DESCRIPTOR_EXIT_FLAG) ?
" flags" : "" );
}
/** Return an estimate of which fraction of usable paths through the Tor
@@ -2207,15 +2230,9 @@ compute_frac_paths_available(const networkstatus_t *consensus,
});
}
/* All nodes with exit flag
* If we're in a network with TestingDirAuthVoteExit set,
* this can cause false positives on have_consensus_path,
* incorrectly setting it to CONSENSUS_PATH_EXIT. This is
* an unavoidable feature of forcing authorities to declare
* certain nodes as exits.
*/
/* All nodes with exit policy and flag */
count_usable_descriptors(&np, &nu, exits, consensus, now,
NULL, USABLE_DESCRIPTOR_EXIT_ONLY);
NULL, USABLE_DESCRIPTOR_EXIT_POLICY_AND_FLAG);
log_debug(LD_NET,
"%s: %d present, %d usable",
"exits",
@@ -2262,43 +2279,28 @@ compute_frac_paths_available(const networkstatus_t *consensus,
smartlist_t *myexits= smartlist_new();
smartlist_t *myexits_unflagged = smartlist_new();
/* All nodes with exit flag in ExitNodes option */
/* All nodes with exit policy and flag in ExitNodes option */
count_usable_descriptors(&np, &nu, myexits, consensus, now,
options->ExitNodes, USABLE_DESCRIPTOR_EXIT_ONLY);
options->ExitNodes,
USABLE_DESCRIPTOR_EXIT_POLICY_AND_FLAG);
log_debug(LD_NET,
"%s: %d present, %d usable",
"myexits",
np,
nu);
/* Now compute the nodes in the ExitNodes option where which we don't know
* what their exit policy is, or we know it permits something. */
/* Now compute the nodes in the ExitNodes option where we know their exit
* policy permits something. */
count_usable_descriptors(&np, &nu, myexits_unflagged,
consensus, now,
options->ExitNodes, USABLE_DESCRIPTOR_ALL);
options->ExitNodes,
USABLE_DESCRIPTOR_EXIT_POLICY);
log_debug(LD_NET,
"%s: %d present, %d usable",
"myexits_unflagged (initial)",
np,
nu);
SMARTLIST_FOREACH_BEGIN(myexits_unflagged, const node_t *, node) {
if (node_has_preferred_descriptor(node, 0) &&
node_exit_policy_rejects_all(node)) {
SMARTLIST_DEL_CURRENT(myexits_unflagged, node);
/* this node is not actually an exit */
np--;
/* this node is unusable as an exit */
nu--;
}
} SMARTLIST_FOREACH_END(node);
log_debug(LD_NET,
"%s: %d present, %d usable",
"myexits_unflagged (final)",
np,
nu);
f_myexit= frac_nodes_with_descriptors(myexits,WEIGHT_FOR_EXIT);
f_myexit_unflagged=
frac_nodes_with_descriptors(myexits_unflagged,WEIGHT_FOR_EXIT);