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• Duplicate IP address detection with multiple NICs

  - by sfink

  I am using arping -D to detect duplicate IP addresses within a network when setting up servers. (The network is controlled by someone else, and we have had many issues with IP allocation in the past.) It works fine as long as my host has a single NIC on a given VLAN, but when my host has more than one (I have one with 9 NICs on one VLAN and 1 on the other), arping -D always returns false collisions. The problem is that all 9 of my NICs respond to an ARP request for any of the IPs on those NICs. (These are real physical NICs, not aliases or anything.) I send out one ARP request packet, and get 9 ARP is-at ARP replies, one for each MAC address. I could implement my own solution by sniffing packets and checking for any replies with a MAC address other than the local NICs', but it seems like there ought to be an easier way.

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• /proc/net/dev and /sys/class/net/ bogus network interface names

  - by sfink

  I am constructing a list of network interfaces to monitor based on the contents of /proc/net/dev. But I am getting some bogus interfaces in the list: __tmp1104705027 __tmp974528607 Where do those come from? They also show up in /sys/class/net/: # ls -1 /sys/class/net/ eth0 eth1 eth2 eth3 lo sit0 __tmp1104705027 __tmp974528607 For now, I think I'll just ignore anything starting with __tmp, but I'd like to know what they are and where they come from. This is on a recompiled CentOS 5.3 kernel: 2.6.18-128.7.1.el5.tvh.7PAE #1 SMP PREEMPT

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• Pre-startup segmentation fault with ptrace

  - by sfink

  I have somehow managed to mangle my computer so that any time I attempt to use something that uses ptrace to trace another process (eg strace, gdb), I get an immediate segmentation fault. For example: # strace /bin/true execve("/bin/true", ["/bin/true"], [/* 27 vars */]) = 0 --- SIGSEGV (Segmentation fault) @ 0 (0) --- +++ killed by SIGSEGV +++ or with gdb: # gdb /bin/true GNU gdb Fedora (6.8-27.el5) Copyright (C) 2008 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later 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"... (no debugging symbols found) (gdb) run Starting program: /bin/true Program terminated with signal SIGSEGV, Segmentation fault. The program no longer exists. You can't do that without a process to debug. rpm -V comes up clean on strace, gdb, and glibc. I do not have any LD_* variables set, and PATH has nothing special in it.

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• Safe way to set computed environment variables

  - by sfink

  I have a bash script that I am modifying to accept key=value pairs from stdin. (It is spawned by xinetd.) How can I safely convert those key=value pairs into environment variables for subprocesses? I plan to only allow keys that begin with a predefined prefix "CMK_", to avoid IFS or any other "dangerous" variable getting set. But the simplistic approach function import () { local IFS="=" while read key val; do case "$key" in CMK_*) eval "$key=$val";; esac done } is horribly insecure because $val could contain all sorts of nasty stuff. This seems like it would work: shopt -s extglob function import () { NORMAL_IFS="$IFS" local IFS="=" while read key val; do case "$key" in CMK_*([a-zA-Z_]) ) IFS="$NORMAL_IFS" eval $key='$val' IFS="=" ;; esac done } but (1) it uses the funky extglob thing that I've never used before, and (2) it's complicated enough that I can't be comfortable that it's secure. My goal, to be specific, is to allow key=value settings to pass through the bash script into the environment of called processes. It is up to the subprocesses to deal with potentially hostile values getting set. I am modifying someone else's script, so I don't want to just convert it to Perl and be done with it. I would also rather not change it around to invoke the subprocesses differently, something like #!/bin/sh ...start of script... perl -nle '($k,$v)=split(/=/,$_,2); $ENV{$k}=$v if $k =~ /^CMK_/; END { exec("subprocess") }' ...end of script...

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