commit 0849d2a2fdaeea2871f32bed35d410f19703aae1 Author: Nick Mathewson nickm@torproject.org Date: Tue Aug 6 11:11:06 2019 -0400
Avoid using labs() on time_t in channeltls.c
On some windows builds, time_t is 64 bits but long is not. This is causing appveyor builds to fail.
Also, one of our uses of labs() on time_t was logically incorrect: it was telling us to accept NETINFO cells up to three minutes _before_ the message they were responding to, which doesn't make sense.
This patch adds a time_abs() function that we should eventually move to intmath.h or something. For now, though, it will make merges easier to have it file-local in channeltls.c.
Fixes bug 31343; bugfix on 0.2.4.4-alpha. --- changes/bug31343 | 9 +++++++++ src/or/channeltls.c | 23 +++++++++++++++++++---- 2 files changed, 28 insertions(+), 4 deletions(-)
diff --git a/changes/bug31343 b/changes/bug31343 new file mode 100644 index 000000000..17a8057ea --- /dev/null +++ b/changes/bug31343 @@ -0,0 +1,9 @@ + o Minor bugfixes (compilation): + - Avoid using labs() on time_t, which can cause compilation warnings + on 64-bit Windows builds. Fixes bug 31343; bugfix on 0.2.4.4-alpha. + + o Minor bugfixes (clock skew detection): + - Don't believe clock skew results from NETINFO cells that appear to + arrive before the VERSIONS cells they are responding to were sent. + Previously, we would accept them up to 3 minutes "in the past". + Fixes bug 31343; bugfix on 0.2.4.4-alpha. diff --git a/src/or/channeltls.c b/src/or/channeltls.c index 3a352d47f..ea69792f1 100644 --- a/src/or/channeltls.c +++ b/src/or/channeltls.c @@ -1584,6 +1584,18 @@ channel_tls_process_versions_cell(var_cell_t *cell, channel_tls_t *chan) }
/** + * Helper: compute the absolute value of a time_t. + * + * (we need this because labs() doesn't always work for time_t, since + * long can be shorter than time_t.) + */ +static inline time_t +time_abs(time_t val) +{ + return (val < 0) ? -val : val; +} + +/** * Process a 'netinfo' cell * * This function is called to handle an incoming NETINFO cell; read and act @@ -1601,7 +1613,7 @@ channel_tls_process_netinfo_cell(cell_t *cell, channel_tls_t *chan) uint8_t n_other_addrs; time_t now = time(NULL);
- long apparent_skew = 0; + time_t apparent_skew = 0; tor_addr_t my_apparent_addr = TOR_ADDR_NULL;
tor_assert(cell); @@ -1659,7 +1671,11 @@ channel_tls_process_netinfo_cell(cell_t *cell, channel_tls_t *chan)
/* Decode the cell. */ timestamp = ntohl(get_uint32(cell->payload)); - if (labs(now - chan->conn->handshake_state->sent_versions_at) < 180) { + const time_t sent_versions_at = + chan->conn->handshake_state->sent_versions_at; + if (now > sent_versions_at && (now - sent_versions_at) < 180) { + /* If we have gotten the NETINFO cell reasonably soon after having + * sent our VERSIONS cell, maybe we can learn skew information from it. */ apparent_skew = now - timestamp; }
@@ -1705,7 +1721,7 @@ channel_tls_process_netinfo_cell(cell_t *cell, channel_tls_t *chan) /* Act on apparent skew. */ /** Warn when we get a netinfo skew with at least this value. */ #define NETINFO_NOTICE_SKEW 3600 - if (labs(apparent_skew) > NETINFO_NOTICE_SKEW && + if (time_abs(apparent_skew) && router_get_by_id_digest(chan->conn->identity_digest)) { int trusted = router_digest_is_trusted_dir(chan->conn->identity_digest); clock_skew_warning(TO_CONN(chan->conn), apparent_skew, trusted, LD_GENERAL, @@ -2182,4 +2198,3 @@ channel_tls_process_authenticate_cell(var_cell_t *cell, channel_tls_t *chan)
#undef ERR } -