gdb for sshd core

##  THIS IS PART OF A MUCH LARGER THREAD - PLEASE START HERE
##		http://pastebin.com/KWZBSD4C

# gdb /usr/sbin/sshd core-sshd-11-0-0-2307-1356920817
GNU gdb (GDB) CentOS (7.0.1-42.el5.centos.1)
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /usr/sbin/sshd...Reading symbols from /usr/lib/debug/usr/sbin/sshd.debug...done.
done.
BFD: Warning: /tmp/core/core-sshd-11-0-0-2307-1356920817 is truncated: expected core file size >= 806912, found: 802816.
[New Thread 2307]
Reading symbols from /lib64/libwrap.so.0...Reading symbols from /usr/lib/debug/lib64/libwrap.so.0.7.6.debug...done.
done.
Loaded symbols for /lib64/libwrap.so.0
Reading symbols from /lib64/libpam.so.0...Reading symbols from /usr/lib/debug/lib64/libpam.so.0.81.5.debug...done.
done.
Loaded symbols for /lib64/libpam.so.0
Reading symbols from /lib64/libdl.so.2...Reading symbols from /usr/lib/debug/lib64/libdl-2.5.so.debug...done.
done.
Loaded symbols for /lib64/libdl.so.2
Reading symbols from /lib64/libselinux.so.1...
warning: the debug information found in "/usr/lib/debug//lib64/libselinux.so.1.debug" does not match "/lib64/libselinux.so.1" (CRC mismatch).


warning: the debug information found in "/usr/lib/debug/lib64/libselinux.so.1.debug" does not match "/lib64/libselinux.so.1" (CRC mismatch).

(no debugging symbols found)...done.
Loaded symbols for /lib64/libselinux.so.1
Reading symbols from /lib64/libaudit.so.0...(no debugging symbols found)...done.
Loaded symbols for /lib64/libaudit.so.0
Reading symbols from /usr/lib64/libfipscheck.so.1...Reading symbols from /usr/lib/debug/usr/lib64/libfipscheck.so.1.1.0.debug...done.
done.
Loaded symbols for /usr/lib64/libfipscheck.so.1
Reading symbols from /lib64/libcrypto.so.6...Reading symbols from /usr/lib/debug/lib64/libcrypto.so.0.9.8e.debug...done.
done.
Loaded symbols for /lib64/libcrypto.so.6
Reading symbols from /lib64/libutil.so.1...Reading symbols from /usr/lib/debug/lib64/libutil-2.5.so.debug...done.
done.
Loaded symbols for /lib64/libutil.so.1
Reading symbols from /lib64/libz.so.1...
warning: the debug information found in "/usr/lib/debug//lib64/libz.so.1.2.3.debug" does not match "/lib64/libz.so.1" (CRC mismatch).


warning: the debug information found in "/usr/lib/debug/lib64/libz.so.1.2.3.debug" does not match "/lib64/libz.so.1" (CRC mismatch).

(no debugging symbols found)...done.
Loaded symbols for /lib64/libz.so.1
Reading symbols from /lib64/libnsl.so.1...Reading symbols from /usr/lib/debug/lib64/libnsl-2.5.so.debug...done.
done.
Loaded symbols for /lib64/libnsl.so.1
Reading symbols from /lib64/libcrypt.so.1...Reading symbols from /usr/lib/debug/lib64/libcrypt-2.5.so.debug...done.
done.
Loaded symbols for /lib64/libcrypt.so.1
Reading symbols from /lib64/libresolv.so.2...Reading symbols from /usr/lib/debug/lib64/libresolv-2.5.so.debug...done.
done.
Loaded symbols for /lib64/libresolv.so.2
Reading symbols from /usr/lib64/libgssapi_krb5.so.2...Reading symbols from /usr/lib/debug/usr/lib64/libgssapi_krb5.so.2.2.debug...done.
done.
Loaded symbols for /usr/lib64/libgssapi_krb5.so.2
Reading symbols from /usr/lib64/libkrb5.so.3...Reading symbols from /usr/lib/debug/usr/lib64/libkrb5.so.3.3.debug...done.
done.
Loaded symbols for /usr/lib64/libkrb5.so.3
Reading symbols from /usr/lib64/libk5crypto.so.3...Reading symbols from /usr/lib/debug/usr/lib64/libk5crypto.so.3.1.debug...done.
done.
Loaded symbols for /usr/lib64/libk5crypto.so.3
Reading symbols from /lib64/libcom_err.so.2...Reading symbols from /usr/lib/debug/lib64/libcom_err.so.2.1.debug...done.
done.
Loaded symbols for /lib64/libcom_err.so.2
Reading symbols from /usr/lib64/libnss3.so...Reading symbols from /usr/lib/debug/usr/lib64/libnss3.so.debug...done.
done.
Loaded symbols for /usr/lib64/libnss3.so
Reading symbols from /lib64/libc.so.6...Reading symbols from /usr/lib/debug/lib64/libc-2.5.so.debug...(no debugging symbols found)...done.
(no debugging symbols found)...done.
Loaded symbols for /lib64/libc.so.6
Reading symbols from /lib64/ld-linux-x86-64.so.2...Reading symbols from /usr/lib/debug/lib64/ld-2.5.so.debug...done.
done.
Loaded symbols for /lib64/ld-linux-x86-64.so.2
Reading symbols from /lib64/libsepol.so.1...Reading symbols from /usr/lib/debug/lib64/libsepol.so.1.debug...done.
done.
Loaded symbols for /lib64/libsepol.so.1
Reading symbols from /usr/lib64/libkrb5support.so.0...Reading symbols from /usr/lib/debug/usr/lib64/libkrb5support.so.0.1.debug...done.
done.
Loaded symbols for /usr/lib64/libkrb5support.so.0
Reading symbols from /lib64/libkeyutils.so.1...(no debugging symbols found)...done.
Loaded symbols for /lib64/libkeyutils.so.1
Reading symbols from /usr/lib64/libnssutil3.so...Reading symbols from /usr/lib/debug/usr/lib64/libnssutil3.so.debug...done.
done.
Loaded symbols for /usr/lib64/libnssutil3.so
Reading symbols from /usr/lib64/libplc4.so...Reading symbols from /usr/lib/debug/usr/lib64/libplc4.so.debug...done.
done.
Loaded symbols for /usr/lib64/libplc4.so
Reading symbols from /usr/lib64/libplds4.so...Reading symbols from /usr/lib/debug/usr/lib64/libplds4.so.debug...done.
done.
Loaded symbols for /usr/lib64/libplds4.so
Reading symbols from /usr/lib64/libnspr4.so...Reading symbols from /usr/lib/debug/usr/lib64/libnspr4.so.debug...done.
done.
Loaded symbols for /usr/lib64/libnspr4.so
Reading symbols from /lib64/libpthread.so.0...Reading symbols from /usr/lib/debug/lib64/libpthread-2.5.so.debug...done.
[Thread debugging using libthread_db enabled]
done.
Loaded symbols for /lib64/libpthread.so.0
Reading symbols from /lib64/libnss_files.so.2...Reading symbols from /usr/lib/debug/lib64/libnss_files-2.5.so.debug...done.
done.
Loaded symbols for /lib64/libnss_files.so.2
Core was generated by `sshd: [accepted]              '.
Program terminated with signal 11, Segmentation fault.
#0  0x00005555373478a0 in ?? ()
(gdb) backtrace
#0  0x00005555373478a0 in ?? ()
#1  0x0000555555560b94 in sshd_exchange_identification (ac=<value optimized out>, av=<value optimized out>) at sshd.c:422
#2  main (ac=<value optimized out>, av=<value optimized out>) at sshd.c:1721
(gdb) frame 0
#0  0x00005555373478a0 in ?? ()
(gdb) list
1726            authctxt = xmalloc(sizeof(*authctxt));
1727            memset(authctxt, 0, sizeof(*authctxt));
1728
1729            authctxt->loginmsg = &loginmsg;
1730
1731            /* XXX global for cleanup, access from other modules */
1732            the_authctxt = authctxt;
1733
1734            /* prepare buffer to collect messages to display to user after login */
1735            buffer_init(&loginmsg);
(gdb) info frame
Stack level 0, frame at 0x7fff7675beb0:
 rip = 0x5555373478a0; saved rip 0x555555560b94
 called by frame at 0x7fff7675cf20
 Arglist at 0x7fff7675bea0, args:
 Locals at 0x7fff7675bea0, Previous frame's sp is 0x7fff7675beb0
 Saved registers:
  rip at 0x7fff7675bea8
(gdb) info locals
No symbol table info available.
(gdb) info args
No symbol table info available.
(gdb) frame 1
#1  0x0000555555560b94 in sshd_exchange_identification (ac=<value optimized out>, av=<value optimized out>) at sshd.c:422
422             client_version_string = xstrdup(buf);
(gdb) list
417                             buf[i] = 0;
418                             break;
419                     }
420             }
421             buf[sizeof(buf) - 1] = 0;
422             client_version_string = xstrdup(buf);
423
424             /*
425              * Check that the versions match.  In future this might accept
426              * several versions and set appropriate flags to handle them
(gdb) info frame
Stack level 1, frame at 0x7fff7675cf20:
 rip = 0x555555560b94 in sshd_exchange_identification (sshd.c:422); saved rip 0x2b4236bb9994
 inlined into frame 2, caller of frame at 0x7fff7675beb0
 source language c.
 Arglist at unknown address.
 Locals at unknown address, Previous frame's sp is 0x7fff7675beb0
 Saved registers:
  rip at 0x7fff7675bea8
(gdb) info locals
No locals.
(gdb) info args
sock_out = <value optimized out>
sock_in = <value optimized out>
(gdb) frame 2
#2  main (ac=<value optimized out>, av=<value optimized out>) at sshd.c:1721
1721            sshd_exchange_identification(sock_in, sock_out);
(gdb) list
1716             */
1717            signal(SIGALRM, grace_alarm_handler);
1718            if (!debug_flag)
1719                    alarm(options.login_grace_time);
1720
1721            sshd_exchange_identification(sock_in, sock_out);
1722
1723            packet_set_nonblocking();
1724
1725            /* allocate authentication context */
(gdb) info frame
Stack level 2, frame at 0x7fff7675cf20:
 rip = 0x555555560b94 in main (sshd.c:1721); saved rip 0x2b4236bb9994
 caller of frame at 0x7fff7675cf20
 source language c.
 Arglist at 0x7fff7675bea8, args: ac=<value optimized out>, av=<value optimized out>
 Locals at 0x7fff7675bea8, Previous frame's sp is 0x7fff7675cf20
 Saved registers:
  rbx at 0x7fff7675cee8, rbp at 0x7fff7675cef0, r12 at 0x7fff7675cef8, r13 at 0x7fff7675cf00, r14 at 0x7fff7675cf08,
  r15 at 0x7fff7675cf10, rip at 0x7fff7675cf18
(gdb) info locals
opt = <value optimized out>
j = <value optimized out>
i = <value optimized out>
on = 1
sock_in = 3
sock_out = 3
newsock = -1
pid = <value optimized out>
fromlen = 875909808
fdset = <value optimized out>
from = {ss_family = 8, __ss_align = 0,
  __ss_padding = "\020\026|UUU\000\000\000\020\000\000\000\000\000\000p\204\331\064\001\000\000\000`\023\375\067B+\000\000`c64B+\000\000p\317uv\377\177\000\000\000`64B+\000\000\374\205UUUU\000\000\000\020\000\000\000\000\000\000\260m3\000\000\000\000\000 \320uv\000\000\000\000 \320uv\377\177\000\000\370\317uv\377\177\000\000\004\000\000\000\000\000\000"}
remote_ip = 0x5555557c8bb0 "127.0.0.1"
remote_port = <value optimized out>
f = <value optimized out>
ai = <value optimized out>
ntop = "?\313uv\377\177\000\000\004\000\000\000\000\000\000\000\240\276f6B+\000\000\305Z54B+\000\000\220\071\067\064B+\000\000\310\004\270\064B+\000\000\220\271f6B+\000\000`\000\000\000\000\000\000\000H\352\356\066B+\000\000P\305uv\377\177\000\000\000\000\000\000\000\000\000\000A\000\000\000\000\000\000\000\062\000\000\000\000\000\000\000\001", '\000' <repeats 39 times>, "\031\004F&\000\001\240\252\360\317uv\377\177\000\000x\271f6B+\000\000\204\030\002\302\220\b\"\000\t\200\000\000\200\006H\204\000\313uv\b\000\000\000p\313uv\377\177\000\000 [{UUU", '\000' <repeats 26 times>"\340, \351\356\066B+\000\000\032\000\000\000\000\000\000\000\062\000\000\000\000\000\000\000\220\312uv\377\177\000\000\000\000\000\000\000\000\000\000\030\000\000\000\000\000\000\000\256"...
strport = "0\000\000\000\000\000\000\000\300kV4B+\000\000@\316YUUU\000\000[\334UUUU\000"
line = <value optimized out>
listen_sock = <value optimized out>
maxfd = 1612748323
startup_p = {-1, -1}
config_s = {-1, -1}
startups = 1987431168
key = <value optimized out>
authctxt = <value optimized out>
ret = <value optimized out>
key_used = 32767
cfg = {buf = 0x5555557c8f50 "u\225\222+\365*\240\251\373\016\345\276HC\237\261\210\232\310(Fy\214\233\232\fxC", alloc = 0,
  offset = 0, end = 526}
(gdb) info args
ac = <value optimized out>
av = <value optimized out>