The following was reported by Pavel Březina <pbrezina@redhat.com>:

We found a crash in SSSD when a tevent signal is freed in its handler, tevent than crashes when it access siginfo.

sig_info is freed in signal destructor:

> #ifdef SA_SIGINFO
>         if (se->sa_flags & SA_SIGINFO) {
>             if (sig_state->sig_info[se->signum]) {
>                 talloc_free(sig_state->sig_info[se->signum]);
>                 sig_state->sig_info[se->signum] = NULL;
>             }
>         }
> #endif

(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

But then it is accessed again in tevent_common_check_signal:

> #ifdef SA_SIGINFO
>         if (clear_processed_siginfo) {
>             uint32_t j;
>             for (j=0;j<count;j++) {
>                 uint32_t ofs = (counter.seen + j)
>                     % TEVENT_SA_INFO_QUEUE_COUNT;
>                 memset((void*)&sig_state->sig_info[i][ofs],
>                     '\0',
>                     sizeof(siginfo_t));
>             }
>         }
> #endif

(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