Basic backend for the protocol-versions voting algorithm.

[This is a brute-force method that potentially uses way too much
RAM. Need to rethink this a little. Right now you can DOS an
authority by saying "Foo=1-4294967295".]
This commit is contained in:
Nick Mathewson 2016-08-19 18:04:02 -04:00
parent 7f718c46f3
commit c1be8f9d57
3 changed files with 251 additions and 0 deletions

View File

@ -309,6 +309,223 @@ encode_protocol_list(const smartlist_t *sl)
return result;
}
/** Voting helper: Given a list of proto_entry_t, return a newly allocated
* smartlist of newly allocated strings, one for each included protocol
* version. (So 'Foo=3,5-7' expands to a list of 'Foo=3', 'Foo=5', 'Foo=6',
* 'Foo=7'.)
*
* Do not list any protocol version more than once. */
static smartlist_t *
expand_protocol_list(const smartlist_t *protos)
{
// XXXX This can make really huge lists from small inputs; that's a DoS
// problem.
smartlist_t *expanded = smartlist_new();
if (!protos)
return expanded;
SMARTLIST_FOREACH_BEGIN(protos, const proto_entry_t *, ent) {
const char *name = ent->name;
SMARTLIST_FOREACH_BEGIN(ent->ranges, const proto_range_t *, range) {
uint32_t u;
for (u = range->low; u <= range->high; ++u) {
smartlist_add_asprintf(expanded, "%s=%lu", name, (unsigned long)u);
}
} SMARTLIST_FOREACH_END(range);
} SMARTLIST_FOREACH_END(ent);
smartlist_sort_strings(expanded);
smartlist_uniq_strings(expanded); // This makes voting work. do not remove
return expanded;
}
/** Voting helper: compare two singleton proto_entry_t items by version
* alone. (A singleton item is one with a single range entry where
* low==high.) */
static int
cmp_single_ent_by_version(const void **a_, const void **b_)
{
const proto_entry_t *ent_a = *a_;
const proto_entry_t *ent_b = *b_;
tor_assert(smartlist_len(ent_a->ranges) == 1);
tor_assert(smartlist_len(ent_b->ranges) == 1);
const proto_range_t *a = smartlist_get(ent_a->ranges, 0);
const proto_range_t *b = smartlist_get(ent_b->ranges, 0);
tor_assert(a->low == a->high);
tor_assert(b->low == b->high);
if (a->low < b->low) {
return -1;
} else if (a->low == b->low) {
return 0;
} else {
return 1;
}
}
/** Voting helper: Given a list of singleton protocol strings (of the form
* Foo=7), return a canonical listing of all the protocol versions listed,
* with as few ranges as possible, with protocol versions sorted lexically and
* versions sorted in numerically increasing order, using as few range entries
* as possible.
**/
static char *
contract_protocol_list(const smartlist_t *proto_strings)
{
// map from name to list of single-version entries
strmap_t *entry_lists_by_name = strmap_new();
// list of protocol names
smartlist_t *all_names = smartlist_new();
// list of strings for the output we're building
smartlist_t *chunks = smartlist_new();
// Parse each item and stick it entry_lists_by_name. Build
// 'all_names' at the same time.
SMARTLIST_FOREACH_BEGIN(proto_strings, const char *, s) {
proto_entry_t *ent = parse_single_entry(s, s+strlen(s));
if (BUG(!ent))
continue;
smartlist_t *lst = strmap_get(entry_lists_by_name, ent->name);
if (!lst) {
smartlist_add(all_names, ent->name);
lst = smartlist_new();
strmap_set(entry_lists_by_name, ent->name, lst);
}
smartlist_add(lst, ent);
} SMARTLIST_FOREACH_END(s);
// We want to output the protocols sorted by their name.
smartlist_sort_strings(all_names);
SMARTLIST_FOREACH_BEGIN(all_names, const char *, name) {
const int first_entry = (name_sl_idx == 0);
smartlist_t *lst = strmap_get(entry_lists_by_name, name);
tor_assert(lst);
// Sort every entry with this name by version. They are
// singletons, so there can't be overlap.
smartlist_sort(lst, cmp_single_ent_by_version);
if (! first_entry)
smartlist_add(chunks, tor_strdup(" "));
/* We're going to construct this entry from the ranges. */
proto_entry_t *entry = tor_malloc_zero(sizeof(proto_entry_t));
entry->ranges = smartlist_new();
entry->name = tor_strdup(name);
// Now, find all the ranges of versions start..end where
// all of start, start+1, start+2, ..end are included.
int start_of_cur_series = 0;
while (start_of_cur_series < smartlist_len(lst)) {
const proto_entry_t *ent = smartlist_get(lst, start_of_cur_series);
const proto_range_t *range = smartlist_get(ent->ranges, 0);
const uint32_t ver_low = range->low;
uint32_t ver_high = ver_low;
int idx;
for (idx = start_of_cur_series+1; idx < smartlist_len(lst); ++idx) {
ent = smartlist_get(lst, idx);
range = smartlist_get(ent->ranges, 0);
if (range->low != ver_high + 1)
break;
ver_high += 1;
}
// Now idx is either off the end of the list, or the first sequence
// break in the list.
start_of_cur_series = idx;
proto_range_t *new_range = tor_malloc_zero(sizeof(proto_range_t));
new_range->low = ver_low;
new_range->high = ver_high;
smartlist_add(entry->ranges, new_range);
}
proto_entry_encode_into(chunks, entry);
proto_entry_free(entry);
} SMARTLIST_FOREACH_END(name);
// Build the result...
char *result = smartlist_join_strings(chunks, "", 0, NULL);
// And free all the stuff we allocated.
SMARTLIST_FOREACH_BEGIN(all_names, const char *, name) {
smartlist_t *lst = strmap_get(entry_lists_by_name, name);
tor_assert(lst);
SMARTLIST_FOREACH(lst, proto_entry_t *, e, proto_entry_free(e));
smartlist_free(lst);
} SMARTLIST_FOREACH_END(name);
strmap_free(entry_lists_by_name, NULL);
smartlist_free(all_names);
SMARTLIST_FOREACH(chunks, char *, cp, tor_free(cp));
smartlist_free(chunks);
return result;
}
/**
* Protocol voting implementation.
*
* Given a list of strings describing protocol versions, return a newly
* allocated string encoding all of the protocols that are listed by at
* least <b>threshold</b> of the inputs.
*
* The string is minimal and sorted according to the rules of
* contract_protocol_list above.
*/
char *
compute_protover_vote(const smartlist_t *list_of_proto_strings,
int threshold)
{
// XXXX This algorithm can be made to use too much RAM. Fix that.
smartlist_t *all_entries = smartlist_new();
// First, parse the inputs and break them into singleton entries.
SMARTLIST_FOREACH_BEGIN(list_of_proto_strings, const char *, vote) {
smartlist_t *unexpanded = parse_protocol_list(vote);
smartlist_t *this_vote = expand_protocol_list(unexpanded);
smartlist_add_all(all_entries, this_vote);
smartlist_free(this_vote);
SMARTLIST_FOREACH(unexpanded, proto_entry_t *, e, proto_entry_free(e));
smartlist_free(unexpanded);
} SMARTLIST_FOREACH_END(vote);
// Now sort the singleton entries
smartlist_sort_strings(all_entries);
// Now find all the strings that appear at least 'threshold' times.
smartlist_t *include_entries = smartlist_new();
const char *cur_entry = smartlist_get(all_entries, 0);
int n_times = 0;
SMARTLIST_FOREACH_BEGIN(all_entries, const char *, ent) {
if (!strcmp(ent, cur_entry)) {
n_times++;
} else {
if (n_times >= threshold)
smartlist_add(include_entries, (void*)cur_entry);
cur_entry = ent;
n_times = 1 ;
}
} SMARTLIST_FOREACH_END(ent);
if (n_times >= threshold)
smartlist_add(include_entries, (void*)cur_entry);
// Finally, compress that list.
char *result = contract_protocol_list(include_entries);
smartlist_free(include_entries);
SMARTLIST_FOREACH(all_entries, char *, cp, tor_free(cp));
smartlist_free(all_entries);
return result;
}
/** Return true if every protocol version described in the string <b>s</b> is
* one that we support, and false otherwise. If <b>missing_out</b> is
* provided, set it to the list of protocols we do not support.

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@ -27,6 +27,9 @@ int protover_all_supported(const char *s, char **missing);
int protover_is_supported_here(protocol_type_t pr, uint32_t ver);
const char *get_supported_protocols(void);
char * compute_protover_vote(const smartlist_t *list_of_proto_strings,
int threshold);
void protover_free_all(void);
#ifdef PROTOVER_PRIVATE

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@ -80,12 +80,43 @@ test_protover_parse(void *arg)
tor_free(re_encoded);
}
static void
test_protover_vote(void *arg)
{
(void) arg;
smartlist_t *lst = smartlist_new();
char *result = compute_protover_vote(lst, 1);
tt_str_op(result, OP_EQ, "");
tor_free(result);
smartlist_add(lst, (void*) "Foo=1-10,500 Bar=1,3-7,8");
result = compute_protover_vote(lst, 1);
tt_str_op(result, OP_EQ, "Bar=1,3-8 Foo=1-10,500");
tor_free(result);
smartlist_add(lst, (void*) "Quux=123-456,78 Bar=2-6,8 Foo=9");
result = compute_protover_vote(lst, 1);
tt_str_op(result, OP_EQ, "Bar=1-8 Foo=1-10,500 Quux=78,123-456");
tor_free(result);
result = compute_protover_vote(lst, 2);
tt_str_op(result, OP_EQ, "Bar=3-6,8 Foo=9");
tor_free(result);
done:
tor_free(result);
smartlist_free(lst);
}
#define PV_TEST(name, flags) \
{ #name, test_protover_ ##name, (flags), NULL, NULL }
struct testcase_t protover_tests[] = {
PV_TEST(parse, 0),
PV_TEST(vote, 0),
END_OF_TESTCASES
};