On Tue, 27 Jun 2023 21:40:14 +0200 Paul Gevers wrote:
> Source: nmap, udptunnel
> Control: found -1 nmap/7.94+dfsg1-1
> Control: found -1 udptunnel/1.1-9
...
> With a recent upload of nmap the autopkgtest of udptunnel fails in
> testing when that autopkgtest is run with the binary packages of nmap
> from unstable. It passes when run with only packages from testing.
I think this is likely to be a bug in nmap ncat, when I remove
udptunnel from the script by connecting ncat directly to ncat,
then the failure still happens with the autopkgtest.
I was able to reproduce this issue outside a chroot. I have attached a
pair of scripts; bad fails and good succeeds. In the good case, I use
`sleep` to hold stdin of `ncat -l` open for 2s, in the bad case I let
it use the stdin provided by the shell (a GNOME terminal pty here).
Looking at the diff between the verbose logs is interesting.
In the good case one select fd is ready and one becomes ready later,
the latter one gets used, but in the bad case both fds appear to be
ready immediately but neither of them get used.
-NCAT DEBUG: select returned 1 fds ready
-NCAT DEBUG: fd 3 is ready
-NCAT DEBUG: selecting, fdmax 3
-NCAT DEBUG: select returned 1 fds ready
+NCAT DEBUG: select returned 2 fds ready
So the issue can be worked around in the udptunnel script by piping
sleep to the ncat listener instead of launching ncat and then sleeping,
or the ncat change that caused this can get bisected and fixed.
--
bye,
pabs
https://wiki.debian.org/PaulWise
bad
Description: application/shellscript
+ rm rx tx
+ echo foo
+ sleep 2s
+ ncat - -u -l 127.0.0.1 1234
Ncat: Version 7.94 ( https://nmap.org/ncat )
NCAT DEBUG: Initialized fdlist with 102 maxfds
Ncat: Listening on 127.0.0.1:1234
NCAT DEBUG: Added fd 3 to list, nfds 1, maxfd 3
NCAT DEBUG: Added fd 0 to list, nfds 2, maxfd 3
NCAT DEBUG: Initialized fdlist with 100 maxfds
NCAT DEBUG: selecting, fdmax 3
+ ncat -u 127.0.0.1 1234
NCAT DEBUG: select returned 1 fds ready
NCAT DEBUG: fd 3 is ready
NCAT DEBUG: Swapping fd[0] (3) with fd[1] (0)
NCAT DEBUG: Removed fd 3 from list, nfds 1, maxfd 0
Ncat: Connection from 127.0.0.1:57558.
NCAT DEBUG: Added fd 3 to list, nfds 2, maxfd 3
NCAT DEBUG: Added fd 3 to list, nfds 1, maxfd 3
NCAT DEBUG: selecting, fdmax 3
NCAT DEBUG: select returned 2 fds ready
NCAT DEBUG: fd 0 is ready
NCAT DEBUG: EOF on stdin
+ sleep 2s
+ head -vn-0 tx rx
==> tx <==
foo
==> rx <==
+ echo tx
tx
+ hd tx
66 6f 6f 0a |foo.|
0004
+ echo rx
rx
+ hd rx
+ echo diff
diff
+ diff -u tx rx
--- tx 2023-07-23 16:49:32.411502343 +0800
+++ rx 2023-07-23 16:49:32.411502343 +0800
@@ -1 +0,0 @@
-foo
good
Description: application/shellscript
+ rm rx tx
+ echo foo
+ + sleep 2sncat
-u 127.0.0.1 1234
+ ncat - -u -l 127.0.0.1 1234
Ncat: Version 7.94 ( https://nmap.org/ncat )
NCAT DEBUG: Initialized fdlist with 102 maxfds
Ncat: Listening on 127.0.0.1:1234
NCAT DEBUG: Added fd 3 to list, nfds 1, maxfd 3
NCAT DEBUG: Added fd 0 to list, nfds 2, maxfd 3
NCAT DEBUG: Initialized fdlist with 100 maxfds
NCAT DEBUG: selecting, fdmax 3
NCAT DEBUG: select returned 1 fds ready
NCAT DEBUG: fd 3 is ready
NCAT DEBUG: Swapping fd[0] (3) with fd[1] (0)
NCAT DEBUG: Removed fd 3 from list, nfds 1, maxfd 0
Ncat: Connection from 127.0.0.1:36688.
NCAT DEBUG: Added fd 3 to list, nfds 2, maxfd 3
NCAT DEBUG: Added fd 3 to list, nfds 1, maxfd 3
NCAT DEBUG: selecting, fdmax 3
NCAT DEBUG: select returned 1 fds ready
NCAT DEBUG: fd 3 is ready
NCAT DEBUG: selecting, fdmax 3
+ sleep 2s
NCAT DEBUG: select returned 1 fds ready
NCAT DEBUG: fd 0 is ready
NCAT DEBUG: EOF on stdin
+ head -vn-0 tx rx
==> tx <==
foo
==> rx <==
foo
+ echo tx
tx
+ hd tx
66 6f 6f 0a |foo.|
0004
+ echo rx
rx
+ hd rx
66 6f 6f 0a |foo.|
0004
+ echo diff
diff
+ diff -u tx rx
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