A [ Regression potential ] section was added to the description.
@Łukasz Zemczak let me know if there are other details you would like.
Thank you!
** Description changed:
-
[Impact]
In some cases, ipconfig can take a longer time than the user-specified
timeouts, causing unexpected delays.
[Test Plan]
Any situation where ipconfig encounters an error sending the DHCP packet, it
will automatically set a delay of 10 seconds, which could be longer than the
user-specified timeout. It can be reproduced by creating a dummy interface and
attempting to run ipconfig on it with a timeout value of less than 10:
# ip link add eth1 type dummy
# date; /usr/lib/klibc/bin/ipconfig -t 2 eth1; date
Thu Nov 18 04:46:13 EST 2021
IP-Config: eth1 hardware address ae:e0:f5:9d:7e:00 mtu 1500 DHCP RARP
IP-Config: no response after 2 secs - giving up
Thu Nov 18 04:46:23 EST 2021
^ Notice above, ipconfig thinks that it waited 2 seconds, but the
timestamps show an actual delay of 10 seconds.
[Where problems could occur]
Please see reproduction steps above. We are seeing this in production too
(see comment #2).
[Other Info]
A patch to fix the issue is being proposed here. It is a safe fix - it only
checks before going into sleep that the timeout never exceeds the
user-requested value.
[Original Description]
In some cases, ipconfig can take longer than the user-specified
timeouts, causing unexpected delays.
in main.c, in function loop(), the process can go into
process_timeout_event() (or process_receive_event() ) and if it
encounters an error situation, will set an attempt to "try again later"
at time equal now + 10 seconds by setting
s->expire = now + 10;
This can happen at any time during the main event loop, which can end up
extending the user-specified timeout if "now + 10" is greater than
"start_time + user-specified-timeout".
I believe a patch like the following is needed to avoid this problem:
--- a/usr/kinit/ipconfig/main.c
+++ b/usr/kinit/ipconfig/main.c
@@ -437,6 +437,13 @@ static int loop(void)
if (timeout > s->expire - now.tv_sec)
timeout = s->expire - now.tv_sec;
+
+ /* Compensate for already-lost time */
+ gettimeofday(&now, NULL);
+ if (now.tv_sec + timeout > start + loop_timeout) {
+ timeout = loop_timeout - (now.tv_sec - start);
+ printf("Lowered timeout to match user request
= (%d s) \n", timeout);
+ }
}
I believe the current behaviour is buggy. This is confirmed when the
following line is executed:
if (loop_timeout >= 0 &&
now.tv_sec - start >= loop_timeout) {
printf("IP-Config: no response after %d "
"secs - giving up\n", loop_timeout);
rc = -1;
goto bail;
}
'loop_timeout' is the user-specified time-out. With a value of 2, in
case of error, this line prints:
IP-Config: no response after 2 secs - giving up
So it thinks that it waited 2 seconds - however, in reality it had
actually waited for 10 seconds.
The suggested code-change ensures that the timeout that is actually used
never exceeds the user-specified timeout.
+
+
+ [ Regression potential ]
+
+ This change ensures that user-specified timeouts are never exceeded, which is
a problem that appears to happen only in case of interface errors.
+ It may be that someone is relying on current behaviour where they receive
DHCP offers after their specified timeout (but within the 10-second error
timeout). However, 1) that is buggy behaviour and should be exposed. Such a
user would need to update their specified timeout to make it long enough to
receive the DHCP offer (setting the timeout to 10 would keep the existing
behaviour). 2) I think it is unlikely that such a scenario exists at all. The
10-second timeout problem happens when there are problems with the interface
that prevent it from even sending out the DHCP request. I think it is very
unlikely (or even, impossible) that DHCP offers would be received on a dead
interface.
+
+ Based on the above points, I consider the regression potential to be
+ very low for this change. I do not expect anyone who is currently using
+ ipconfig successfully to notice this change.
+
+ I believe the only difference introduced by this is the reduction of
+ delays caused by dead or problematic network interfaces. Those error
+ delays are shortened such that they never exceeed user-specified
+ timeouts.
--
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https://bugs.launchpad.net/bugs/1947099
Title:
ipconfig does not honour user-requested timeouts in some cases
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