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SubjectTraceroute without s bit
Hi all,

I wrote a small traceroute last night that works mostly like the
LBL one, except it doesn't need an s bit anymore :)

Since the source code is small, I'm attaching it to this mail.
Note that it requires a 2.4 linux kernel and possibly a recent
glibc (not sure of that).

Most of the features it uses are standard BSD stack ones, except
for the use of IP-level control messages to obtain the ICMP error
codes and the error's time stamp.

There are three things that puzzle me, however:

1. When I want to include IP options into an outgoing packet,
I'm expected to include a struct ip_options in the IP_RETOPTS
control message. However, this struct is included in
#ifdef __KERNEL__/#endif in 2.4.0-t10 (on which I'm compiling
right now). Normally this doesn't deter me, but in this case
some of the fields look sort of fishy to me.

My question is, do we really want to allow users to hand
an arbitrary, unchecked struct ip_options to the kernel?
Wouldn't raw options be a better choice?

2. There's another issue with ip_cmsg_send in ip_sockglue.c;
it allows any user to specify PKTINFO data in a control
messages. As far as I can tell, by looking at udp.c,
this lets any user set arbitrary IP source addresses
on outgoing UDP packets. Yikes.

3. There seems to be a bug somewhere in the handling of poll().
If you observe the traceroute process with strace, you'll
notice that it starts spinning madly after receiving the
first bunch of packets (those with ttl 1).

13:43:02 poll([{fd=4, events=POLLERR}], 1, 5) = 0
13:43:02 poll([{fd=4, events=POLLERR}], 1, 5) = 0
13:43:02 poll([{fd=4, events=POLLERR}], 1, 5) = 0
13:43:02 poll([{fd=4, events=POLLERR}], 1, 5) = 0

I.e. the poll call returns as if it had timed out, but it

Any input from network kernel hackers would be greatly appreciated!

Olaf Kirch | --- o --- Nous sommes du soleil we love when we play | / | \ sol.dhoop.naytheet.ah +-------------------- Why Not?! -----------------------
UNIX, n.: Spanish manufacturer of fire extinguishers.
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