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Avoid using labs() on time_t in channeltls.c

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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.
This commit is contained in:
Nick Mathewson 2019-08-06 11:11:06 -04:00
parent fb977f8cac
commit 0849d2a2fd
2 changed files with 28 additions and 4 deletions
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9
changes/bug31343 Normal file
View File

@ -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.

23
src/or/channeltls.c
View File

@ -1583,6 +1583,18 @@ 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
*
@ -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
}