double free in digest-md5

[Simo Sorce]

Hi Philipp,
I created PR #562 which should handle this issue, would be nice if you
could try it out and confirm it resolve the crashes for you.

Simo.

On Tue, 2019-04-16 at 09:03 +0200, Philipp Gesang wrote:
> Hi,
> 
> this is an issue I originally raised on the mutt-users list [0]
> where it was suggested that I seek assistance here. The MUA
> crashes when sending email over a digest-md5 authenticated
> connection. This happens in a call to sasl_dispose() that
> indirectly frees some handle that had been freed earlier while
> authenticating.
> 
> Backtraces:
> 
> --8<-- free 1 ----------------------------------------------->8--
> 
> #0  free_rc4 (text=text at entry=0x21d3460) at digestmd5.c:1227
> #1  0x00007f1fa8416b92 in make_client_response (text=text at entry=0x21d3460, 
>     params=params at entry=0x21d3200, oparams=oparams at entry=0x21d18f0) at digestmd5.c:3613
> #2  0x00007f1fa8417039 in digestmd5_client_mech_step2 (oparams=<optimized out>, 
>     clientoutlen=<optimized out>, clientout=<optimized out>, prompt_need=<optimized out>, 
>     serverinlen=<optimized out>, serverin=<optimized out>, params=0x21d3200, 
>     ctext=<optimized out>) at digestmd5.c:4364
> #3  digestmd5_client_mech_step (conn_context=<optimized out>, params=0x21d3200, 
>     serverin=<optimized out>, serverinlen=<optimized out>, prompt_need=<optimized out>, 
>     clientout=<optimized out>, clientoutlen=<optimized out>, oparams=<optimized out>)
>     at digestmd5.c:4558
> #4  0x00007f1fa7e6a471 in sasl_client_step (conn=0x21d1080, serverin=<optimized out>, 
>     serverinlen=<optimized out>, prompt_need=prompt_need at entry=0x7fffc8656330, 
>     clientout=clientout at entry=0x7fffc8656340, clientoutlen=clientoutlen at entry=0x7fffc865631c)
>     at client.c:922
> #5  0x0000000000492c05 in smtp_auth_sasl (conn=conn at entry=0x210f810, mechlist=<optimized out>)
>     at smtp.c:635
> #6  0x000000000049339d in smtp_auth (conn=0x210f810) at smtp.c:549
> #7  smtp_open (conn=0x210f810) at smtp.c:503
> #8  mutt_smtp_send (from=0x210ce70, to=0x210c890, cc=0x0, bcc=0x0, 
>     msgfile=msgfile at entry=0x7fffc8657570 "/tmp/mutt-drift-2428-105237-294724449650828126", 
>     eightbit=1) at smtp.c:311
> #9  0x0000000000464a45 in send_message (msg=<optimized out>, msg=<optimized out>) at send.c:1030
> #10 ci_send_message (flags=<optimized out>, flags at entry=0, msg=<optimized out>, msg at entry=0x0, 
>     tempfile=tempfile at entry=0x0, ctx=0x1f44270, cur=<optimized out>, cur at entry=0x0) at send.c:1936
> #11 0x000000000042201e in mutt_index_menu () at curs_main.c:2161
> #12 0x0000000000409253 in main (argc=1, argv=0x7fffc865abe8, environ=<optimized out>)
>     at main.c:1274
> 
> --8<-- free 2 ----------------------------------------------->8--
> 
> #0  free_rc4 (text=0x21d3460) at digestmd5.c:1227
> #1  0x00007f1fa8413420 in digestmd5_common_mech_dispose (conn_context=0x21d3460, utils=0x21d32d0)
>     at digestmd5.c:1610
> #2  0x00007f1fa7e696f8 in client_dispose (pconn=0x21d1080) at client.c:337
> #3  0x00007f1fa7e6c414 in sasl_dispose (pconn=0x21693a0) at common.c:849
> #4  0x00000000004987c0 in mutt_sasl_conn_close (conn=0x210f810) at mutt_sasl.c:496
> #5  0x00000000004952a3 in mutt_socket_close (conn=conn at entry=0x210f810) at mutt_socket.c:85
> #6  0x000000000049395a in mutt_smtp_send (from=<optimized out>, to=0x210c890, cc=0x0, bcc=0x0, 
>     msgfile=msgfile at entry=0x7fffc8657570 "/tmp/mutt-drift-2428-105237-294724449650828126", 
>     eightbit=<optimized out>) at smtp.c:357
> #7  0x0000000000464a45 in send_message (msg=<optimized out>, msg=<optimized out>) at send.c:1030
> #8  ci_send_message (flags=<optimized out>, flags at entry=0, msg=<optimized out>, msg at entry=0x0, 
>     tempfile=tempfile at entry=0x0, ctx=0x1f44270, cur=<optimized out>, cur at entry=0x0) at send.c:1936
> #9  0x000000000042201e in mutt_index_menu () at curs_main.c:2161
> #10 0x0000000000409253 in main (argc=1, argv=0x7fffc865abe8, environ=<optimized out>)
>     at main.c:1274
> 
> --8<--------------------------------------------------------->8--
> 
> AFAICT mutt’s smtp client code follows the steps layed out in
> sample/client.c. Is there a precaution to be taken by the caller
> of sasl_client_step() and sasl_dispose() to guard against
> accidentally triggering free_rc4() twice?
> 
> I’ve tested both 2.1.26 and 2.1.27, the issue is present in both.
> FWIW the client authenticates against a postfix built against
> cyrus-sasl 2.1.23. Let me know if you need more information.
> 
> Thanks,
> Philipp
> 
> [0] http://lists.mutt.org/pipermail/mutt-users/Week-of-Mon-20190415/000824.html
> 

-- 
Simo Sorce
Sr. Principal Software Engineer
Red Hat, Inc