I think I've found a bug in libwrap/tcpwrappers. Before filing an actual
bug report I want to get some feedback here first.
A hosts.allow file with ~1000 ips on a single line(Haven't experimented
with other quantities yet), causes network daemons that use libwrap stop
accepting incoming network connections and use 100% cpu on an incoming
connection. This problem appeared because sshguard placed a large
number of IPs in my hosts.allow file triggering this bug.
I've left the affected daemons for a long period of time (once about 8
hours) and they don't seem to come back, so I think this is more than
just it taking a while to loop through a 1000 item array of IPs
The production system that was affected is FreeBSD 7.0-32bit
Test system is FreeBSD 7.1-32bit
Example hosts.allow file (IPs are randomly generated for purposes of
example)
sshd : 112.110.123.63 113.11.2.126 113.11.8.6 113.19.19.22
113.197.48.68 <snipped 990+ IPs> 116.48.108.244 116.48.11.19 : deny
ALL : ALL : allow
top output of affected system. sshd wcpu slowly crawls up to 100% over
about 30 seconds or so.
crash# top
last pid: 692; load averages: 0.08, 0.04,
0.04 up
0+00:12:13 15:42:30
24 processes: 2 running, 22 sleeping
CPU: 49.7% user, 0.0% nice, 0.2% system, 0.2% interrupt, 49.9% idle
Mem: 9304K Active, 6004K Inact, 21M Wired, 32K Cache, 10M Buf, 947M Free
Swap: 1995M Total, 1995M Free
PID USERNAME THR PRI NICE SIZE RES STATE C TIME WCPU
COMMAND
691 root 1 103 0 5760K 3660K CPU1 1 0:04 33.98% sshd
672 root 1 4 0 8436K 3888K sbwait 1 0:00 0.00% sshd
677 cstdenis 1 20 0 4460K 2288K pause 0 0:00 0.00% csh
682 root 1 20 0 5484K 2632K pause 0 0:00 0.00% csh
675 cstdenis 1 44 0 8436K 3896K select 0 0:00 0.00% sshd
<snip>
A backtrace shows
crash# gdb /usr/sbin/sshd 691
GNU gdb 6.1.1 [FreeBSD]
Copyright 2004 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 "i386-marcel-freebsd"...
Attaching to program: /usr/sbin/sshd, process 691
Reading symbols from /usr/lib/libssh.so.4...done.
Loaded symbols for /usr/lib/libssh.so.4
Reading symbols from /lib/libutil.so.7...done.
Loaded symbols for /lib/libutil.so.7
Reading symbols from /lib/libz.so.4...done.
Loaded symbols for /lib/libz.so.4
Reading symbols from /usr/lib/libwrap.so.5...done.
Loaded symbols for /usr/lib/libwrap.so.5
<snip other symbols for breviry>
Reading symbols from /libexec/ld-elf.so.1...done.
Loaded symbols for /libexec/ld-elf.so.1
0x28373225 in fgets (buf=0xbfbfe67b "", n=1, fp=0x283b8040) at
/usr/src/lib/libc/stdio/fgets.c:56
56 {
(gdb) bt
#0 0x28373225 in fgets (buf=0xbfbfe67b "", n=1, fp=0x283b8040) at
/usr/src/lib/libc/stdio/fgets.c:56
#1 0x281124ee in xgets (ptr=0xbfbfe67b "", len=1, fp=0x283b8040) at
/usr/src/lib/libwrap/../../contrib/tcp_wrappers/misc.c:38
#2 0x28111410 in table_match (table=0x28112c5c "/etc/hosts.allow",
request=0xbfbfeb14)
at
/usr/src/lib/libwrap/../../contrib/tcp_wrappers/hosts_access.c:162
#3 0x28111540 in hosts_access (request=0xbfbfeb14) at
/usr/src/lib/libwrap/../../contrib/tcp_wrappers/hosts_access.c:132
#4 0x08052b39 in main (ac=2, av=0xbfbfeecc) at
/usr/src/secure/usr.sbin/sshd/../../../crypto/openssh/sshd.c:1843
(gdb) bt
#0 0x28373225 in fgets (buf=0xbfbfe67b "", n=1, fp=0x283b8040) at
/usr/src/lib/libc/stdio/fgets.c:56
#1 0x281124ee in xgets (ptr=0xbfbfe67b "", len=1, fp=0x283b8040) at
/usr/src/lib/libwrap/../../contrib/tcp_wrappers/misc.c:38
#2 0x28111410 in table_match (table=0x28112c5c "/etc/hosts.allow",
request=0xbfbfeb14)
at
/usr/src/lib/libwrap/../../contrib/tcp_wrappers/hosts_access.c:162
#3 0x28111540 in hosts_access (request=0xbfbfeb14) at
/usr/src/lib/libwrap/../../contrib/tcp_wrappers/hosts_access.c:132
#4 0x08052b39 in main (ac=2, av=0xbfbfeecc) at
/usr/src/secure/usr.sbin/sshd/../../../crypto/openssh/sshd.c:1843
(gdb) q
The program is running. Quit anyway (and detach it)? (y or n) y
Detaching from program: /usr/sbin/sshd, process 691
A few questions
1. Is this a known issue of any sort? I've done some searching on it,
but haven't found anything of interest.
2. Should this be reported to FreeBSD bug tracker, or to libwrap (or
both)? Basically, is FreeBSD's libwrap (more or less) in sync with the
main one, or is it completely separate?
--
Chris St Denis
Programmer
SmarttNet (www.smartt.com)
Ph: 604-473-9700 Ext. 200
-------------------------------------------
"Smart Internet Solutions For Businesses"
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