From 4ea8b443de8be0f7a932f325dfafa1ee2a843795 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= Date: Sun, 17 Jan 2021 19:51:28 +0100 Subject: [PATCH] resolved: fix use-after-free with queries hitting the cache MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When dns_transaction_complete() manages to resolve a query, it invalidates the query candidate object. It shall not be accessed afterwards. We have the following chain of calls: dns_query_candidate_go → dns_transaction_go → dns_transaction_prepare → dns_cache_lookup (success: 1) → dns_transaction_complete After returning back to dns_query_candidate_go(), we'd attempt to continue iteration over the list of transactions attached to the query candidate, accessing already freed (and overwritten) memory: (gdb) bt 0 0x00007f637297cf47 in hashmap_iterate_entry (i=0x7ffe7e15cc90, h=0x706f746b73656465) at ../src/basic/hashmap.c:703 1 _hashmap_iterate (h=0x706f746b73656465, i=i@entry=0x7ffe7e15cc90, value=value@entry=0x7ffe7e15cc88, key=key@entry=0x0) at ../src/basic/hashmap.c:712 2 0x00007f637297d01b in set_iterate (s=, i=i@entry=0x7ffe7e15cc90, value=value@entry=0x7ffe7e15cc88) at ../src/basic/hashmap.c:733 hence we crash 3 0x0000557bc99eb80f in dns_query_candidate_go (c=c@entry=0x557bcaf86890) at ../src/resolve/resolved-dns-query.c:139 ...but c is not valid here in the second iteration of the loop 4 0x0000557bc99eb720 in dns_query_candidate_notify (c=0x557bcaf86890) at ../src/resolve/resolved-dns-query.c:271 c was valid here at entry... 5 0x0000557bc99efe28 in dns_transaction_complete (t=0x557bcac072f0, state=) at ../src/resolve/resolved-dns-transaction.c:350 t is a valid transaction (11481 in the backtrace below) 6 0x0000557bc99f1efb in dns_transaction_process_reply (t=0x557bcac072f0, p=) at ../src/resolve/resolved-dns-transaction.c:1171 7 0x0000557bc99f2d41 in on_dns_packet (s=, fd=, revents=, userdata=0x557bcac072f0) at ../src/resolve/resolved-dns-transaction.c:1223 8 0x00007f6372a25217 in source_dispatch (s=s@entry=0x557bcb162c50) at ../src/libsystemd/sd-event/sd-event.c:3181 9 0x00007f6372a254fd in sd_event_dispatch (e=0x557bcb15b050) at ../src/libsystemd/sd-event/sd-event.c:3620 10 0x00007f6372a267c8 in sd_event_run (e=e@entry=0x557bcb15b050, timeout=timeout@entry=18446744073709551615) at ../src/libsystemd/sd-event/sd-event.c:3678 11 0x00007f6372a269ef in sd_event_loop (e=0x557bcb15b050) at ../src/libsystemd/sd-event/sd-event.c:3700 12 0x0000557bc99ddc14 in run (argc=, argv=) at ../src/resolve/resolved.c:92 13 0x0000557bc99d260a in main (argc=, argv=) at ../src/resolve/resolved.c:99 xxx.name.net systemd-resolved[31705]: Got message type=method_call sender=:1.3644 destination=org.freedesktop.resolve1 path=/org/freedesktop/resolve1 interface=org.freedesktop.resolve1.Manager member=ResolveHostname cookie=2 reply_cookie=0 signature=isit error-name=n/a error-message=n/a xxx.name.net systemd-resolved[31705]: idn2_lookup_u8: xxx → xxx xxx.name.net systemd-resolved[31705]: Looking up RR for xxx IN A. xxx.name.net systemd-resolved[31705]: Sent message type=method_call sender=n/a destination=org.freedesktop.DBus path=/org/freedesktop/DBus interface=org.freedesktop.DBus member=AddMatch cookie=1102 reply_cookie=0 signature=s error-name=n/a error-message=n/a xxx.name.net systemd-resolved[31705]: Sent message type=method_call sender=n/a destination=org.freedesktop.DBus path=/org/freedesktop/DBus interface=org.freedesktop.DBus member=GetNameOwner cookie=1103 reply_cookie=0 signature=s error-name=n/a error-message=n/a xxx.name.net systemd-resolved[31705]: Got message type=method_return sender=org.freedesktop.DBus destination=:1.3324 path=n/a interface=n/a member=n/a cookie=4294967295 reply_cookie=1103 signature=s error-name=n/a error-message=n/a xxx.name.net systemd-resolved[31705]: Cache miss for xxx.name.net IN A xxx.name.net systemd-resolved[31705]: Transaction 11481 for scope dns on enp42s0/*. xxx.name.net systemd-resolved[31705]: Using feature level UDP for transaction 11481. xxx.name.net systemd-resolved[31705]: Using DNS server 192.168.1.1 for transaction 11481. xxx.name.net systemd-resolved[31705]: Sending query packet with id 11481 of size 35. xxx.name.net systemd-resolved[31705]: Got message type=method_return sender=org.freedesktop.DBus destination=:1.3324 path=n/a interface=n/a member=n/a cookie=4294967295 reply_cookie=1102 signature= error-name=n/a error-message=n/a xxx.name.net systemd-resolved[31705]: Match type='signal',sender='org.freedesktop.DBus',path='/org/freedesktop/DBus',interface='org.freedesktop.DBus',member='NameOwnerChanged',arg0=':1.3644' successfully installed. xxx.name.net systemd-resolved[31705]: Processing incoming packet on transaction 11481 (rcode=NXDOMAIN). xxx.name.net systemd-resolved[31705]: Not caching negative entry without a SOA record: xxx.name.net IN A xxx.name.net systemd-resolved[31705]: Transaction 11481 for on scope dns on enp42s0/* now complete with from network (unsigned). xxx.name.net systemd-resolved[31705]: Positive cache hit for xxx.lan IN A xxx.name.net systemd-resolved[31705]: Transaction 64364 for on scope dns on enp42s0/* now complete with from cache (unsigned). xxx.name.net systemd-resolved[31705]: Sent message type=method_return sender=n/a destination=:1.3644 path=n/a interface=n/a member=n/a cookie=1104 reply_cookie=2 signature=a(iiay)st error-name=n/a error-message=n/a xxx.name.net systemd-resolved[31705]: Sent message type=method_call sender=n/a destination=org.freedesktop.DBus path=/org/freedesktop/DBus interface=org.freedesktop.DBus member=RemoveMatch cookie=1105 reply_cookie=0 signature=s error-name=n/a error-message=n/a xxx.name.net systemd-resolved[31705]: Freeing transaction 64364. xxx.name.net systemd[1]: systemd-resolved.service: Main process exited, code=dumped, status=11/SEGV xxx.name.net systemd[1]: systemd-resolved.service: Failed with result 'core-dump'. Fixes #16168, https://bugzilla.redhat.com/show_bug.cgi?id=1895937. --- src/resolve/resolved-dns-query.c | 14 ++++++++++++-- src/resolve/resolved-dns-transaction.c | 16 ++++++++++------ 2 files changed, 22 insertions(+), 8 deletions(-) diff --git a/src/resolve/resolved-dns-query.c b/src/resolve/resolved-dns-query.c index c4d620ac8b7..757fbedf991 100644 --- a/src/resolve/resolved-dns-query.c +++ b/src/resolve/resolved-dns-query.c @@ -133,23 +133,33 @@ static int dns_query_candidate_go(DnsQueryCandidate *c) { DnsTransaction *t; int r; unsigned n = 0; + bool notify = false; assert(c); + c->query->block_ready++; + /* Start the transactions that are not started yet */ SET_FOREACH(t, c->transactions) { if (t->state != DNS_TRANSACTION_NULL) continue; r = dns_transaction_go(t); - if (r < 0) + if (r < 0) { + c->query->block_ready--; return r; + } + if (r == 0) + /* A transaction is complete. */ + notify = true; n++; } + c->query->block_ready--; + /* If there was nothing to start, then let's proceed immediately */ - if (n == 0) + if (n == 0 || notify) dns_query_candidate_notify(c); return 0; diff --git a/src/resolve/resolved-dns-transaction.c b/src/resolve/resolved-dns-transaction.c index b20a61a4018..7c966affe1b 100644 --- a/src/resolve/resolved-dns-transaction.c +++ b/src/resolve/resolved-dns-transaction.c @@ -152,8 +152,8 @@ bool dns_transaction_gc(DnsTransaction *t) { static uint16_t pick_new_id(Manager *m) { uint16_t new_id; - /* Find a fresh, unused transaction id. Note that this loop is bounded because there's a limit on the number of - * transactions, and it's much lower than the space of IDs. */ + /* Find a fresh, unused transaction id. Note that this loop is bounded because there's a limit on the + * number of transactions, and it's much lower than the space of IDs. */ assert_cc(TRANSACTIONS_MAX < 0xFFFF); @@ -1333,6 +1333,10 @@ static int dns_transaction_prepare(DnsTransaction *t, usec_t ts) { assert(t); + /* Returns 0 if dns_transaction_complete() has been called. In that case the transaction and query + * candidate objects may have been invalidated and must not be accessed. Returns 1 if the transaction + * has been prepared. */ + dns_transaction_stop_timeout(t); if (!dns_scope_network_good(t->scope)) { @@ -1460,7 +1464,6 @@ static int dns_transaction_prepare(DnsTransaction *t, usec_t ts) { } static int dns_transaction_make_packet_mdns(DnsTransaction *t) { - _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL; bool add_known_answers = false; DnsTransaction *other; @@ -1628,8 +1631,9 @@ int dns_transaction_go(DnsTransaction *t) { assert(t); - /* Returns > 0 if the transaction is now pending, returns 0 if could be processed immediately and has finished - * now. */ + /* Returns > 0 if the transaction is now pending, returns 0 if could be processed immediately and has + * finished now. In the latter case, the transaction and query candidate objects must not be accessed. + */ assert_se(sd_event_now(t->scope->manager->event, clock_boottime_or_monotonic(), &ts) >= 0); @@ -1687,7 +1691,7 @@ int dns_transaction_go(DnsTransaction *t) { t->state = DNS_TRANSACTION_PENDING; log_debug("Delaying %s transaction for " USEC_FMT "us.", dns_protocol_to_string(t->scope->protocol), jitter); - return 0; + return 1; } /* Otherwise, we need to ask the network */