From eb966928428a80c105d33bd60bcae5503a1adeb7 Mon Sep 17 00:00:00 2001 From: Isis Lovecruft Date: Thu, 29 Mar 2018 01:54:05 +0000 Subject: [PATCH 1/5] protover: TROVE-2018-005 Fix potential DoS in protover protocol parsing. MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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" […] "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` prior to #24031, and a `HashMap` 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 45f0377d61..24b3813614 100644 --- a/src/or/protover.c +++ b/src/or/protover.c @@ -50,6 +50,11 @@ 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. @@ -195,6 +200,15 @@ 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); @@ -397,6 +411,14 @@ 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 9b94044b91..66deb7551c 100644 --- a/src/test/test_protover.c +++ b/src/test/test_protover.c @@ -110,6 +110,12 @@ test_protover_parse_fail(void *arg) 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); + done: ; } @@ -203,6 +209,15 @@ 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); @@ -270,6 +285,15 @@ test_protover_all_supported(void *arg) tor_end_capture_bugs_(); #endif + /* 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); From b681438daf06d8d5b1c67d8c78f1b041f9b1f5b8 Mon Sep 17 00:00:00 2001 From: Isis Lovecruft Date: Mon, 7 May 2018 23:59:06 +0000 Subject: [PATCH 2/5] vote: TROVE-2018-005 Make DirAuths omit misbehaving routers from their vote. --- src/or/dirserv.c | 6 ++++++ src/or/protover.c | 12 ++++++++++++ src/or/protover.h | 1 + 3 files changed, 19 insertions(+) diff --git a/src/or/dirserv.c b/src/or/dirserv.c index 95bef9889d..68df1c4676 100644 --- a/src/or/dirserv.c +++ b/src/or/dirserv.c @@ -2943,6 +2943,12 @@ dirserv_generate_networkstatus_vote_obj(crypto_pk_t *private_key, microdescriptors = smartlist_new(); SMARTLIST_FOREACH_BEGIN(routers, routerinfo_t *, ri) { + /* If it has a protover list and contains a protocol name greater than + * MAX_PROTOCOL_NAME_LENGTH, skip it. */ + if (ri->protocol_list && + protover_contains_long_protocol_names(ri->protocol_list)) { + continue; + } if (ri->cache_info.published_on >= cutoff) { routerstatus_t *rs; vote_routerstatus_t *vrs; diff --git a/src/or/protover.c b/src/or/protover.c index 24b3813614..94e6b11c46 100644 --- a/src/or/protover.c +++ b/src/or/protover.c @@ -273,6 +273,18 @@ parse_protocol_list(const char *s) return NULL; } +/** + * Return true if the unparsed protover in s would contain a protocol + * name longer than MAX_PROTOCOL_NAME_LENGTH, and false otherwise. + */ +bool +protover_contains_long_protocol_names(const char *s) +{ + if (!parse_protocol_list(s)) + return true; + return false; +} + /** * Given a protocol type and version number, return true iff we know * how to speak that protocol. diff --git a/src/or/protover.h b/src/or/protover.h index 657977279e..8b2db85d77 100644 --- a/src/or/protover.h +++ b/src/or/protover.h @@ -38,6 +38,7 @@ typedef enum protocol_type_t { PRT_CONS, } protocol_type_t; +bool protover_contains_long_protocol_names(const char *s); int protover_all_supported(const char *s, char **missing); int protover_is_supported_here(protocol_type_t pr, uint32_t ver); const char *protover_get_supported_protocols(void); From bc2d6876b3f64497f66eca0ecc150696f476e401 Mon Sep 17 00:00:00 2001 From: Nick Mathewson Date: Tue, 22 May 2018 12:15:52 -0400 Subject: [PATCH 3/5] Add stdbool to protover.h. Only needed for the 032 backport --- src/or/protover.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/or/protover.h b/src/or/protover.h index 8b2db85d77..ab7f4d1dd9 100644 --- a/src/or/protover.h +++ b/src/or/protover.h @@ -10,7 +10,7 @@ #define TOR_PROTOVER_H #include "container.h" - +#include /** The first version of Tor that included "proto" entries in its * descriptors. Authorities should use this to decide whether to * guess proto lines. */ From d2bc019053058b09b5552d327106d9fbe0acad56 Mon Sep 17 00:00:00 2001 From: Nick Mathewson Date: Tue, 22 May 2018 12:21:00 -0400 Subject: [PATCH 4/5] changes file for TROVE-2018-005 --- changes/TROVE-2018-005 | 6 ++++++ 1 file changed, 6 insertions(+) create mode 100644 changes/TROVE-2018-005 diff --git a/changes/TROVE-2018-005 b/changes/TROVE-2018-005 new file mode 100644 index 0000000000..769c653f43 --- /dev/null +++ b/changes/TROVE-2018-005 @@ -0,0 +1,6 @@ + o Major bugfixes (security, directory authority, denial-of-service): + - Fix a bug that could have allowed an attacker to force a + directory authority to use up all its RAM by passing it a + maliciously crafted protocol versions string. Fixes bug 25517; + bugfix on 0.2.9.4-alpha. This issue is also tracked as + TROVE-2018-005. From 569b4e57e23d728969a12751afc6b45f32d0f093 Mon Sep 17 00:00:00 2001 From: Isis Lovecruft Date: Wed, 21 Mar 2018 02:22:54 +0000 Subject: [PATCH 5/5] rust: Mirror TROVE-2018-005 fix in Rust protover implementation. * REFACTORS `UnvalidatedProtoEntry::from_str` to place the bulk of the splitting/parsing logic in to a new `UnvalidatedProtoEntry::parse_protocol_and_version_str()` method (so that both `from_str()` and `from_str_any_len()` can call it.) * ADD a new `UnvalidatedProtoEntry::from_str_any_len()` method in order to maintain compatibility with consensus methods older than 29. * ADD a limit on the number of characters in a protocol name. * FIXES part of #25517: https://bugs.torproject.org/25517 --- src/rust/protover/ffi.rs | 14 ++++-- src/rust/protover/protover.rs | 93 ++++++++++++++++++++++++++++++----- 2 files changed, 91 insertions(+), 16 deletions(-) diff --git a/src/rust/protover/ffi.rs b/src/rust/protover/ffi.rs index a40353eb13..ed078654f7 100644 --- a/src/rust/protover/ffi.rs +++ b/src/rust/protover/ffi.rs @@ -59,7 +59,8 @@ pub extern "C" fn protover_all_supported( Err(_) => return 1, }; - let relay_proto_entry: UnvalidatedProtoEntry = match relay_version.parse() { + let relay_proto_entry: UnvalidatedProtoEntry = + match UnvalidatedProtoEntry::from_str_any_len(relay_version) { Ok(n) => n, Err(_) => return 1, }; @@ -181,6 +182,7 @@ pub extern "C" fn protover_get_supported_protocols() -> *const c_char { pub extern "C" fn protover_compute_vote( list: *const Stringlist, threshold: c_int, + allow_long_proto_names: bool, ) -> *mut c_char { if list.is_null() { @@ -195,9 +197,13 @@ pub extern "C" fn protover_compute_vote( let mut proto_entries: Vec = Vec::new(); for datum in data { - let entry: UnvalidatedProtoEntry = match datum.parse() { - Ok(x) => x, - Err(_) => continue, + let entry: UnvalidatedProtoEntry = match allow_long_proto_names { + true => match UnvalidatedProtoEntry::from_str_any_len(datum.as_str()) { + Ok(n) => n, + Err(_) => continue}, + false => match datum.parse() { + Ok(n) => n, + Err(_) => continue}, }; proto_entries.push(entry); } diff --git a/src/rust/protover/protover.rs b/src/rust/protover/protover.rs index 5e5a31cd33..17a8d60ec6 100644 --- a/src/rust/protover/protover.rs +++ b/src/rust/protover/protover.rs @@ -28,6 +28,9 @@ const FIRST_TOR_VERSION_TO_ADVERTISE_PROTOCOLS: &'static str = "0.2.9.3-alpha"; /// C_RUST_COUPLED: src/or/protover.c `MAX_PROTOCOLS_TO_EXPAND` const MAX_PROTOCOLS_TO_EXPAND: usize = (1<<16); +/// The maximum size an `UnknownProtocol`'s name may be. +pub(crate) const MAX_PROTOCOL_NAME_LENGTH: usize = 100; + /// Currently supported protocols and their versions, as a byte-slice. /// /// # Warning @@ -114,6 +117,18 @@ impl FromStr for UnknownProtocol { type Err = ProtoverError; fn from_str(s: &str) -> Result { + if s.len() <= MAX_PROTOCOL_NAME_LENGTH { + Ok(UnknownProtocol(s.to_string())) + } else { + Err(ProtoverError::ExceedsNameLimit) + } + } +} + +impl UnknownProtocol { + /// Create an `UnknownProtocol`, ignoring whether or not it + /// exceeds MAX_PROTOCOL_NAME_LENGTH. + fn from_str_any_len(s: &str) -> Result { Ok(UnknownProtocol(s.to_string())) } } @@ -428,6 +443,49 @@ impl UnvalidatedProtoEntry { }; supported_versions.iter().any(|v| v.1 >= *vers) } + + /// Split a string containing (potentially) several protocols and their + /// versions into a `Vec` of tuples of string in `(protocol, versions)` + /// form. + /// + /// # Inputs + /// + /// A &str in the form `"Link=3-4 Cons=5"`. + /// + /// # Returns + /// + /// A `Result` whose `Ok` variant is a `Vec<(&str, &str)>` of `(protocol, + /// versions)`, or whose `Err` variant is a `ProtoverError`. + /// + /// # Errors + /// + /// This will error with a `ProtoverError::Unparseable` if any of the + /// following are true: + /// + /// * If a protocol name is an empty string, e.g. `"Cons=1,3 =3-5"`. + /// * If a protocol name cannot be parsed as utf-8. + /// * If the version numbers are an empty string, e.g. `"Cons="`. + fn parse_protocol_and_version_str<'a>(protocol_string: &'a str) + -> Result, ProtoverError> + { + let mut protovers: Vec<(&str, &str)> = Vec::new(); + + for subproto in protocol_string.split(' ') { + let mut parts = subproto.splitn(2, '='); + + let name = match parts.next() { + Some("") => return Err(ProtoverError::Unparseable), + Some(n) => n, + None => return Err(ProtoverError::Unparseable), + }; + let vers = match parts.next() { + Some(n) => n, + None => return Err(ProtoverError::Unparseable), + }; + protovers.push((name, vers)); + } + Ok(protovers) + } } impl FromStr for UnvalidatedProtoEntry { @@ -460,19 +518,10 @@ impl FromStr for UnvalidatedProtoEntry { /// * If the version string is malformed. See `impl FromStr for ProtoSet`. fn from_str(protocol_string: &str) -> Result { let mut parsed: UnvalidatedProtoEntry = UnvalidatedProtoEntry::default(); + let parts: Vec<(&str, &str)> = + UnvalidatedProtoEntry::parse_protocol_and_version_str(protocol_string)?; - for subproto in protocol_string.split(' ') { - let mut parts = subproto.splitn(2, '='); - - let name = match parts.next() { - Some("") => return Err(ProtoverError::Unparseable), - Some(n) => n, - None => return Err(ProtoverError::Unparseable), - }; - let vers = match parts.next() { - Some(n) => n, - None => return Err(ProtoverError::Unparseable), - }; + for &(name, vers) in parts.iter() { let versions = ProtoSet::from_str(vers)?; let protocol = UnknownProtocol::from_str(name)?; @@ -482,6 +531,26 @@ impl FromStr for UnvalidatedProtoEntry { } } +impl UnvalidatedProtoEntry { + /// Create an `UnknownProtocol`, ignoring whether or not it + /// exceeds MAX_PROTOCOL_NAME_LENGTH. + pub(crate) fn from_str_any_len(protocol_string: &str) + -> Result + { + let mut parsed: UnvalidatedProtoEntry = UnvalidatedProtoEntry::default(); + let parts: Vec<(&str, &str)> = + UnvalidatedProtoEntry::parse_protocol_and_version_str(protocol_string)?; + + for &(name, vers) in parts.iter() { + let versions = ProtoSet::from_str(vers)?; + let protocol = UnknownProtocol::from_str_any_len(name)?; + + parsed.insert(protocol, versions); + } + Ok(parsed) + } +} + /// Pretend a `ProtoEntry` is actually an `UnvalidatedProtoEntry`. impl From for UnvalidatedProtoEntry { fn from(proto_entry: ProtoEntry) -> UnvalidatedProtoEntry {