commit c56bb300447688788cb4c78c0290bc95386e63d9 Author: Nick Mathewson nickm@torproject.org Date: Mon Dec 9 11:02:34 2013 -0500

Remove a check in channeltls.c that could never fail.

We were checking whether a 8-bit length field had overflowed a 503-byte buffer. Unless somebody has found a way to store "504" in a single byte, it seems unlikely.

Fix for 10313 and 9980. Based on a pach by Jared L Wong. First found by David Fifield with STACK. --- changes/bug10313 | 8 ++++++++ src/or/channeltls.c | 14 ++++++++------ 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/changes/bug10313 b/changes/bug10313 new file mode 100644 index 0000000..b29d4da --- /dev/null +++ b/changes/bug10313 @@ -0,0 +1,8 @@ + o Minor bugfixes: + - Fixed an erroneous pointer comparison that would have allowed + compilers to remove a bounds check in channeltls.c. The fix + was to remove the check entirely, since it was impossible for + the code to overflow the bounds. Noticed by Jared L + Wong. Fixes bug 10313 and 9980. Bugfix on 0.2.0.10-alpha. + + diff --git a/src/or/channeltls.c b/src/or/channeltls.c index f751c0d..e622f2f 100644 --- a/src/or/channeltls.c +++ b/src/or/channeltls.c @@ -1408,12 +1408,14 @@ channel_tls_process_netinfo_cell(cell_t *cell, channel_tls_t *chan) my_addr_ptr = (uint8_t*) cell->payload + 6; end = cell->payload + CELL_PAYLOAD_SIZE; cp = cell->payload + 6 + my_addr_len; - if (cp >= end) { - log_fn(LOG_PROTOCOL_WARN, LD_OR, - "Addresses too long in netinfo cell; closing connection."); - connection_or_close_for_error(chan->conn, 0); - return; - } else if (my_addr_type == RESOLVED_TYPE_IPV4 && my_addr_len == 4) { + + /* We used to check: + * if (my_addr_len >= CELL_PAYLOAD_SIZE - 6) { + * + * This is actually never going to happen, since my_addr_len is at most 255, + * and CELL_PAYLOAD_LEN - 6 is 503. So we know that cp is < end. */ + + if (my_addr_type == RESOLVED_TYPE_IPV4 && my_addr_len == 4) { tor_addr_from_ipv4n(&my_apparent_addr, get_uint32(my_addr_ptr)); } else if (my_addr_type == RESOLVED_TYPE_IPV6 && my_addr_len == 16) { tor_addr_from_ipv6_bytes(&my_apparent_addr, (const char *) my_addr_ptr);