On (26/05/15 11:04), Pavel Březina wrote:
On 05/26/2015 10:57 AM, Lukas Slebodnik wrote:
>On (26/05/15 10:44), Pavel Březina wrote:
>>On 05/25/2015 02:58 PM, Lukas Slebodnik wrote:
>>>On (22/05/15 11:02), Pavel Březina wrote:
>>>>On 05/20/2015 02:20 PM, Lukas Slebodnik wrote:
>>>>>ehlo,
>>>>>
>>>>>attached patch fixes a crash if return code of proxy_child is not 0.
>>>>>You can reproduce it with sssd in non-root mode or
>>>>>you can replace proxy_child with bash script.
>>>>>
>>>>>I'm not sure about the name of tevent_immediate callback
>>>>>so feel free to propose better name.
>>>>>
>>>>>LS
>>>>
>>>>Hi,
>>>>the whole proxy auth code does not really follow tevent style but I think
>>>>your name is good enough.
>>>>However, I don't see why it should crash, can you
>>>>explain it in more detail please?
>>>
>>>a) proxy_child_init_send is called
>>> -- request with state "struct pc_init_ctx" is created
>>> -- process is forked
>>> -- parent register signal SIGCHLD with clallback pc_init_sig_handler
>>>b) child return non-zero
>>> -- parent recieve pc_init_sig_handler
>>>c) pc_init_sig_handler is executed
>>> -- unused argument "__siginfo" contains NON null data
>>> -- tevent_req_error(req, EIO) is called
>>> -- proxy_child_init_done callback is called
>>> -- request is released (including "struct tevent_signal" and all
related data)
>>> -- unused argument "__siginfo" is NULL now
>>>d) function pc_init_sig_handler finished
>>> -- we are back in tevent code from singnal handler
>>> -- tevent wants to do some clean-up and dereference NULL in memset
>>>
>>>It is not clear from back trace but the 1st argument of memset is NULL.
>>>
>>>(gdb) bt
>>>#0 0x00007fd7ba400505 in memset (__len=<optimized out>,
__ch=<optimized out>, __dest=<optimized out>) at
/usr/include/bits/string3.h:84
>>>#1 tevent_common_check_signal (ev=0x7fd7bfddf670) at ../tevent_signal.c:459
>>>#2 0x00007fd7ba40228c in epoll_event_loop (tvalp=0x7fff85536430,
epoll_ev=0x7fd7bfddf8b0) at ../tevent_epoll.c:647
>>>#3 epoll_event_loop_once (ev=<optimized out>, location=<optimized
out>) at ../tevent_epoll.c:926
>>>#4 0x00007fd7ba4007d7 in std_event_loop_once (ev=0x7fd7bfddf670,
location=0x7fd7bdb417c3 "src/util/server.c:668") at ../tevent_standard.c:114
>>>#5 0x00007fd7ba3fcfbd in _tevent_loop_once (ev=ev@entry=0x7fd7bfddf670,
location=location@entry=0x7fd7bdb417c3 "src/util/server.c:668") at
../tevent.c:530
>>>#6 0x00007fd7ba3fd15b in tevent_common_loop_wait (ev=0x7fd7bfddf670,
location=0x7fd7bdb417c3 "src/util/server.c:668") at ../tevent.c:634
>>>#7 0x00007fd7ba400777 in std_event_loop_wait (ev=0x7fd7bfddf670,
location=0x7fd7bdb417c3 "src/util/server.c:668") at ../tevent_standard.c:140
>>>#8 0x00007fd7bdb29343 in server_loop (main_ctx=0x7fd7bfde0ac0) at
src/util/server.c:668
>>>#9 0x00007fd7be39ca42 in main (argc=8, argv=<optimized out>) at
src/providers/data_provider_be.c:2909
>>>
>>>
>>>BTW it's easily reproducible with proxy provider. I can give you an
access
>>>to such machine.
>>>
>>>I hope it is clear now.
>>>
>>>LS
>>
>>Hi,
>>I'm sorry, but I don't think this is the problem. I'm not saying the
solution
>>may not be right, but the cause is different.
>>
>>1) siginfo is not attached to tevent_signal context, so freeing tevent_signal
>>does not do anything with siginfo
>>
>>>static struct tevent_sig_state {
>>> struct tevent_common_signal_list *sig_handlers[TEVENT_NUM_SIGNALS+1];
>>> struct sigaction *oldact[TEVENT_NUM_SIGNALS+1];
>>> struct tevent_sigcounter signal_count[TEVENT_NUM_SIGNALS+1];
>>> struct tevent_sigcounter got_signal;
>>>#ifdef SA_SIGINFO
>>> /* with SA_SIGINFO we get quite a lot of info per signal */
>>> siginfo_t *sig_info[TEVENT_NUM_SIGNALS+1];
>>> struct tevent_sigcounter sig_blocked[TEVENT_NUM_SIGNALS+1];
>>>#endif
>>>} *sig_state;
>>
>>2) it is a ring buffer, that is the reason why it is cleared in tevent after
>>sighandler is finished
>>
>Yes, it is pointer to ringbuffer.
>But argument "__siginfo" was valid pointer to ringbuffer before calling
>tevent_req_error and after it was NULL. That's the reason why it crashed.
>Dereference of null pointer (in memset)
Yes. But the reason why it is NULL should not be that we freed tevent_signal
from the handler (unless it is a bug in tevent).
It was cleared by tevent_signal_destructor
so it is not bug in tevent. it is by design.
IMHO it make sense. If you release tevent_signal
You do not care anymore about sig_info
Maybe it could be documented in tevent that you should not release
tevent_signal within handler if you created tevent signal with SA_SIGINFO.
(gdb) bt
#0 0x00007f5d4d86cc74 in tevent_signal_destructor (se=0x7f5d5370f920) at
../tevent_signal.c:213
#1 0x00007f5d4d65f233 in _talloc_free_internal () from /lib64/libtalloc.so.2
#2 0x00007f5d4d6593a3 in _talloc_free () from /lib64/libtalloc.so.2
#3 0x00007f5d4342f3d4 in proxy_child_init_done (subreq=0x7f5d5370f600) at
src/providers/proxy/proxy_auth.c:436
#4 0x00007f5d4d86b0c2 in _tevent_req_error (req=req@entry=0x7f5d5370f600,
error=error@entry=5, location=location@entry=0x7f5d43433010
"src/providers/proxy/proxy_auth.c:356")
at ../tevent_req.c:167
#5 0x00007f5d4342ef5e in pc_init_sig_handler (ev=<optimized out>,
sige=<optimized out>, signum=<optimized out>, count=<optimized out>,
__siginfo=<optimized out>, pvt=<optimized out>)
at src/providers/proxy/proxy_auth.c:356
#6 0x00007f5d4d86d48c in tevent_common_check_signal (ev=0x7f5d536de670) at
../tevent_signal.c:428
#7 0x00007f5d4d86f28c in epoll_event_loop (tvalp=0x7fff7b568490, epoll_ev=0x7f5d536de8b0)
at ../tevent_epoll.c:647
#8 epoll_event_loop_once (ev=<optimized out>, location=<optimized out>) at
../tevent_epoll.c:926
#9 0x00007f5d4d86d7d7 in std_event_loop_once (ev=0x7f5d536de670, location=0x7f5d50faedc3
"src/util/server.c:668") at ../tevent_standard.c:114
#10 0x00007f5d4d869fbd in _tevent_loop_once (ev=ev@entry=0x7f5d536de670,
location=location@entry=0x7f5d50faedc3 "src/util/server.c:668") at
../tevent.c:530
#11 0x00007f5d4d86a15b in tevent_common_loop_wait (ev=0x7f5d536de670,
location=0x7f5d50faedc3 "src/util/server.c:668") at ../tevent.c:634
#12 0x00007f5d4d86d777 in std_event_loop_wait (ev=0x7f5d536de670, location=0x7f5d50faedc3
"src/util/server.c:668") at ../tevent_standard.c:140
#13 0x00007f5d50f96863 in server_loop (main_ctx=0x7f5d536dfac0) at src/util/server.c:668
#14 0x00007f5d5180aa42 in main (argc=8, argv=<optimized out>) at
src/providers/data_provider_be.c:2909
>>5) I'm not sure why it crashes, however we can stop using
flag SA_SIGINFO
>>since it is unused anyway, it should do the trick
>>
>That might be a solution too.
>
I tried it and it works.
>>6) freeing tevent_signal causes to run destructor of
pc_init_ctx which sends
>>kill(SIGKILL). Maybe it triggers some tevent bug?
>Do you want to access to a machine to confirm wheter it's tevent bug or no?
>I do not want to dig in tevent :-)
Sure.
will do in private IRC message when you will be online :-)
It's better to double check.
LS