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[tor-commits] [tor/master] protover: TROVE-2018-005 Fix potential DoS in protover protocol parsing.
commit 056be68b1b5a727bb6cb26d98f37bfa131f76701
Author: Isis Lovecruft <isis@xxxxxxxxxxxxxx>
Date: Thu Mar 29 01:54:05 2018 +0000
protover: TROVE-2018-005 Fix potential DoS in protover protocol parsing.
In protover.c, the `expand_protocol_list()` function expands a `smartlist_t` of
`proto_entry_t`s to their protocol name concatenated with each version number.
For example, given a `proto_entry_t` like so:
proto_entry_t *proto = tor_malloc(sizeof(proto_entry_t));
proto_range_t *range = tor_malloc_zero(sizeof(proto_range_t));
proto->name = tor_strdup("DoSaaaaaaaaaaaaaaaaaaaaaa[19KB]aaa");
proto->ranges = smartlist_new();
range->low = 1;
range->high = 65536;
smartlist_add(proto->ranges, range);
(Where `[19KB]` is roughly 19KB of `"a"` bytes.) This would expand in
`expand_protocol_list()` to a `smartlist_t` containing 65536 copies of the
string, e.g.:
"DoSaaaaaaaaaaaaaaaaaaaaaa[19KB]aaa=1"
"DoSaaaaaaaaaaaaaaaaaaaaaa[19KB]aaa=2"
[â?¦]
"DoSaaaaaaaaaaaaaaaaaaaaaa[19KB]aaa=65535"
Thus constituting a potential resource exhaustion attack.
The Rust implementation is not subject to this attack, because it instead
expands the above string into a `HashMap<String, HashSet<u32>` prior to #24031,
and a `HashMap<UnvalidatedProtocol, ProtoSet>` after). Neither Rust version is
subject to this attack, because it only stores the `String` once per protocol.
(Although a related, but apparently of too minor impact to be usable, DoS bug
has been fixed in #24031. [0])
[0]: https://bugs.torproject.org/24031
* ADDS hard limit on protocol name lengths in protover.c and checks in
parse_single_entry() and expand_protocol_list().
* ADDS tests to ensure the bug is caught.
* FIXES #25517: https://bugs.torproject.org/25517
---
src/or/protover.c | 22 ++++++++++++++++++++++
src/test/test_protover.c | 24 ++++++++++++++++++++++++
2 files changed, 46 insertions(+)
diff --git a/src/or/protover.c b/src/or/protover.c
index 18382ba7c..97d436dd1 100644
--- a/src/or/protover.c
+++ b/src/or/protover.c
@@ -53,6 +53,11 @@ static const struct {
#define N_PROTOCOL_NAMES ARRAY_LENGTH(PROTOCOL_NAMES)
+/* Maximum allowed length of any single subprotocol name. */
+// C_RUST_COUPLED: src/rust/protover/protover.rs
+// `MAX_PROTOCOL_NAME_LENGTH`
+static const uint MAX_PROTOCOL_NAME_LENGTH = 100;
+
/**
* Given a protocol_type_t, return the corresponding string used in
* descriptors.
@@ -198,6 +203,15 @@ parse_single_entry(const char *s, const char *end_of_entry)
if (equals == s)
goto error;
+ /* The name must not be longer than MAX_PROTOCOL_NAME_LENGTH. */
+ if (equals - s > MAX_PROTOCOL_NAME_LENGTH) {
+ log_warn(LD_NET, "When parsing a protocol entry, I got a very large "
+ "protocol name. This is possibly an attack or a bug, unless "
+ "the Tor network truly supports protocol names larger than "
+ "%ud characters. The offending string was: %s",
+ MAX_PROTOCOL_NAME_LENGTH, escaped(out->name));
+ goto error;
+ }
out->name = tor_strndup(s, equals-s);
tor_assert(equals < end_of_entry);
@@ -439,6 +453,14 @@ expand_protocol_list(const smartlist_t *protos)
SMARTLIST_FOREACH_BEGIN(protos, const proto_entry_t *, ent) {
const char *name = ent->name;
+ if (strlen(name) > MAX_PROTOCOL_NAME_LENGTH) {
+ log_warn(LD_NET, "When expanding a protocol entry, I got a very large "
+ "protocol name. This is possibly an attack or a bug, unless "
+ "the Tor network truly supports protocol names larger than "
+ "%ud characters. The offending string was: %s",
+ MAX_PROTOCOL_NAME_LENGTH, escaped(name));
+ continue;
+ }
SMARTLIST_FOREACH_BEGIN(ent->ranges, const proto_range_t *, range) {
uint32_t u;
for (u = range->low; u <= range->high; ++u) {
diff --git a/src/test/test_protover.c b/src/test/test_protover.c
index 7bf1471eb..7a4fffad8 100644
--- a/src/test/test_protover.c
+++ b/src/test/test_protover.c
@@ -125,6 +125,13 @@ test_protover_parse_fail(void *arg)
/* Broken range */
elts = parse_protocol_list("Link=1,9-8,3");
tt_ptr_op(elts, OP_EQ, NULL);
+
+ /* Protocol name too long */
+ elts = parse_protocol_list("DoSaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+ "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+ "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa");
+ tt_ptr_op(elts, OP_EQ, NULL);
+
#endif
done:
;
@@ -219,6 +226,15 @@ test_protover_vote(void *arg)
tt_str_op(result, OP_EQ, "");
tor_free(result);
+ /* Protocol name too long */
+ smartlist_clear(lst);
+ smartlist_add(lst, (void*) "DoSaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+ "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+ "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa");
+ result = protover_compute_vote(lst, 1);
+ tt_str_op(result, OP_EQ, "");
+ tor_free(result);
+
done:
tor_free(result);
smartlist_free(lst);
@@ -300,6 +316,14 @@ test_protover_all_supported(void *arg)
tt_assert(protover_all_supported("Sleen=0-4294967295", &msg));
tor_end_capture_bugs_();
+ /* Protocol name too long */
+ tor_capture_bugs_(1);
+ tt_assert(protover_all_supported("DoSaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+ "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+ "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+ "aaaaaaaaaaaa=1-65536", &msg));
+ tor_end_capture_bugs_();
+
done:
tor_end_capture_bugs_();
tor_free(msg);
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