From bd67b23fec5f9312769b9abf26787f074db05217 Mon Sep 17 00:00:00 2001 From: Nick Mathewson Date: Mon, 10 Jan 2011 16:18:32 -0500 Subject: [PATCH] Always nul-terminate the result passed to evdns_server_add_ptr_reply In dnsserv_resolved(), we carefully made a nul-terminated copy of the answer in a PTR RESOLVED cell... then never used that nul-terminated copy. Ouch. Surprisingly this one isn't as huge a security problem as it could be. The only place where the input to dnsserv_resolved wasn't necessarily nul-terminated was when it was called indirectly from relay.c with the contents of a relay cell's payload. If the end of the payload was filled with junk, eventdns.c would take the strdup() of the name [This part is bad; we might crash there if the cell is in a bad part of the stack or the heap] and get a name of at least length 495[*]. eventdns.c then rejects any name of length over 255, so the bogus data would be neither transmitted nor altered. [*] If the name was less than 495 bytes long, the client wouldn't actually be reading off the end of the cell. Nonetheless this is a reasonably annoying bug. Better fix it. Found while looking at bug 2332, reported by doorss. Bugfix on 0.2.0.1-alpha. --- changes/bug2332 | 4 ++++ src/or/dnsserv.c | 2 +- 2 files changed, 5 insertions(+), 1 deletion(-) create mode 100644 changes/bug2332 diff --git a/changes/bug2332 b/changes/bug2332 new file mode 100644 index 0000000000..5f73ddd7af --- /dev/null +++ b/changes/bug2332 @@ -0,0 +1,4 @@ + o Minor bugfixes + - Fix a bug with handling misformed replies to reverse DNS lookup + requests in DNSPort. Bugfix on Tor 0.2.0.1-alpha. Related to a bug + reported by doorss. diff --git a/src/or/dnsserv.c b/src/or/dnsserv.c index 579080be3e..57c449311f 100644 --- a/src/or/dnsserv.c +++ b/src/or/dnsserv.c @@ -275,7 +275,7 @@ dnsserv_resolved(edge_connection_t *conn, char *ans = tor_strndup(answer, answer_len); evdns_server_request_add_ptr_reply(req, NULL, name, - (char*)answer, ttl); + ans, ttl); tor_free(ans); } else if (answer_type == RESOLVED_TYPE_ERROR) { err = DNS_ERR_NOTEXIST;