imap-login SSLv3 causes signal 11, core dump and DoS. ssl_protocols = ??

[James]

On 20/03/2015 18:24, Timo Sirainen wrote:

>> Connecting to dovecot with ssl3 causes imap-login to die:
>>
>> Mar 20 11:30:35 MAILHOST dovecot: [ID 583609 mail.crit] imap-login: Fatal: master: service(imap-login): child 21918 killed with signal 11 (core dumped) [last ip=127.0.0.1]
>
> I can't reproduce it. I tried it with the same ssl_* settings you had. Can you get a gdb backtrace from the crash? It says "core dumped", so I guess there should be a core file somewhere. http://dovecot.org/bugreport.html has some more info on how to get it.


Thank you for your interest, here is a dbx trace.  This was with OpenSSL 
1.0.2a.


(dbx) where 

=>[1] ssl3_get_client_hello(s = 0x809b2a0) (optimized), at 0xfe9db0d5 
(line ~1362) in "s3_srvr.c"
   [2] ssl3_accept(s = 0x809b2a0) (optimized), at 0xfe9d9892 (line ~357) 
in "s3_srvr.c"
   [3] SSL_accept(s = 0x809b2a0) (optimized), at 0xfea09f07 (line ~990) 
in "ssl_lib.c"
   [4] ssl_handshake(proxy = 0x809ba38) (optimized), at 0xfee35c18 (line 
~481) in "ssl-proxy-openssl.c"
   [5] ssl_step(proxy = 0x809ba38) (optimized), at 0xfee35ee0 (line 
~545) in "ssl-proxy-openssl.c"
   [6] ssl_proxy_flush(proxy = 0x809ba38) (optimized), at 0xfee3680c 
(line ~817) in "ssl-proxy-openssl.c"
   [7] ssl_proxy_destroy(proxy = 0x809ba38) (optimized), at 0xfee3686b 
(line ~825) in "ssl-proxy-openssl.c"
   [8] ssl_handle_error(proxy = 0x809ba38, ret = -1, func_name = 
0xfee3b2d8 "SSL_accept()") (optimized), at 0xfee35bc0 (line ~465) in 
"ssl-proxy-openssl.c"
   [9] ssl_handshake(proxy = 0x809ba38) (optimized), at 0xfee35cc9 (line 
~483) in "ssl-proxy-openssl.c"
   [10] ssl_step(proxy = 0x809ba38) (optimized), at 0xfee35ee0 (line 
~545) in "ssl-proxy-openssl.c"
   [11] ssl_proxy_start(proxy = 0x809ba38) (optimized), at 0xfee36341 
(line ~685) in "ssl-proxy-openssl.c"
   [12] client_connected_finish(conn = 0x8047ae0) (optimized), at 
0xfee31d62 (line ~151) in "main.c"
   [13] client_connected(conn = 0x8047ae0) (optimized), at 0xfee32148 
(line ~246) in "main.c"
   [14] master_service_listen(l = 0x8096b30) (optimized), at 0xfecfac7e 
(line ~837) in "master-service.c"
   [15] io_loop_call_io(io = 0x8096bd0) (optimized), at 0xfeda764b (line 
~501) in "ioloop.c"
   [16] io_loop_handler_run_internal(ioloop = 0x8071d70) (optimized), at 
0xfedaa419 (line ~211) in "ioloop-poll.c"
   [17] io_loop_handler_run(ioloop = 0x8071d70) (optimized), at 
0xfeda77be (line ~548) in "ioloop.c"
   [18] io_loop_run(ioloop = 0x8071d70) (optimized), at 0xfeda7711 (line 
~525) in "ioloop.c"
   [19] master_service_run(service = 0x8071cb8, callback = 0xfee32040 = 
&`libdovecot-login.so.0.0.0`main.c`client_connected(struct 
master_service_connection *conn)) (optimized), at 0xfecfa3d7 (line ~569) 
in "master-service.c"
   [20] login_binary_run(binary = 0x8068c50, argc = 2, argv = 0x8047d4c) 
(optimized), at 0xfee3294a (line ~470) in "main.c"
   [21] main(argc = 2, argv = 0x8047d4c) (optimized), at 0x8054de7 (line 
~706) in "client.c"






>> dovecot.conf had:
>> ssl_protocols = !SSLv2 !SSLv3
>>
>> removing that line stops the core dump and syslog then shows:
>>
>> Mar 20 11:36:25 MAILHOST dovecot: [ID 583609 mail.info] imap-login: Disconnected (disconnected before auth was ready, waited 0 secs): user=<>, rip=127.0.0.1, lip=127.0.0.1, TLS handshaking: SSL_accept() failed: error:14076102:SSL routines:SSL23_GET_CLIENT_HELLO:unsupported protocol, session=<eqr1ubYRWgB/AAAB>
>>
>>
>>
>> the "SSL23_GET_CLIENT_HELLO:unsupported protocol" seems to do what I thought the ssl_protocols setting did.
>> Do I still need, if I ever needed, the "ssl_protocols = " setting?
>
> All these ssl_* settings just go to OpenSSL without Dovecot (or I) knowing all that much about them. I think you still need it, but maybe it's because your ssl_cipher_list is so limited that it fails the session anyway (just my guess).

I admit I just copied from somewhere else without full understanding. 
Please if someone can advise me on settings for ssl_protocols and 
ssl_cipher_list then I'll use.

Removing "ssl_cipher_list = ", so using the default, does not cure the 
problem.



James.