libax25 axio_flush bug hangs node and fix

Hi

I noticed that my awznode (a variant of linux node) hangs and use maximum CPU when user starts any external command and incoming AX.25 connection get broken.

After tracing found something strange in libax25-0.0.10 in ax25io.c.

In function static int flush_obuf(ax25io *p)
it returns -1 if write to output file descriptor failed
if ((ret = write(p->ofd, p->obuf, p->optr < p->paclen ? p->optr : p->paclen)) < 0) return -1

but, in axio_flush(ax25io *p)
we have following loop:

while (p->optr) {
                FD_ZERO(&fdset);
                FD_SET(p->ofd, &fdset);   
                if (select(p->ofd+1, NULL, &fdset, NULL, NULL)<0)
                        return -1;
		flushed+=flush_obuf(p);
                flushed+=j;
}

it is obvious that this loop will never end if above mentioned write failed. After breaking this loop if flush_obuf returns -1 my awnnode does not hangs.

Can maintainer of libax25 fix this in next release ?

73 de Tihomir Heidelberg, [email protected]

Are the Symptoms of this shown as -
Internal connections to my Linux_node then onward connection fails. Certain conditions the entry in the node user table stays there until I kill the associated node process.

Also incoming netrom connections to my linux_node where the link breaks between the remote and my system does not clear down and leaves the user entry (USERS command) until I get round to Killing the associated node process. Seem to be from the time I install libax25-0.0.10

I had been thinking that I was looking for a netrom/node patch as I had to rebuild my system in August due to lost of hard disk. and Installed the latest Libax25 as part of the rebuild. de Paul g4apl (gb7cip Caterham_Uk)

In message <13346@9A0TCP>, Tihomir Heidelberg <[email protected]> writes

[email protected]

Hi

it happend when someone connect to node, then execute any external command (that call any linux command) and then connection get broken

but, because axio_flush enters unlimited loop when one end of pipe die, it is very possible that this bug produce also hangs of node in different situations

as I see this loop does not exists in libax25-0.0.9, so I it very possible that I get this problem after installing libax25-0.0.10

at http://ham2.cc.fer.hr/9a4gl/ax25io.patch is patch you can apply to libax25-0.0.10 to see if it helps in your situation

of course, then do:
make
make install
ldconfig

73 de Tihomir, [email protected]

Damn, i thought this been fixed in 10. Tomi and somoene else were discussing it, I'll need their help again.

- Craig

Craig Small VK2XLZ  GnuPG:1C1B D893 1418 2AF4 45EE  95CB C76C E5AC 12CA DFA5
Eye-Net Consulting http://www.enc.com.au/                <[email protected]>
MIEEE <[email protected]>                 Debian developer <[email protected]>

No, actually the bug was introduced in .10 ...

Anyway, I spent last evening thinking back what was discussed with Jeroen last spring and then cleaning up his last patch a bit. I will send that to you in a few days.

Now, the problem is that this patch will revert the "fix" that was tried in 10. Jeroen tried to fix a problem in the applications with a fix in the lib. After the discussion we finally agreed that the .9 behaviour is correct, only a few relatively minor bugs needed to be squashed. The "big" bug is in the applications using libax25io and _they_ need to be fixed.

So finally yesterday I also started to really think how to fix node. The fix won't be trivial but I'll try and produce a working fix soon. Gosh... That would be the first new node release since -99 ...

(If you want a quick fix, then Tihomir's patch seems ok to me. But I really wouldn't like to see that in an official release.)

Tomi Manninen           Internet:  [email protected]
OH2BNS                  AX.25:     [email protected]
KP20ME04                Amprnet:   [email protected]

I am runnung libax25-0.0.7-7 under redhat 7.1, kernel 2.4.19 (2.4.13 was the same). I fell I have the same problem with freezing after broken connections, probably more than just node.
Is this the same bug?
73
Kjell sm7gvf

No it isn't. This bug is only in 0.0.10. What exactly freezes?

Tomi Manninen           Internet:  [email protected]
OH2BNS                  AX.25:     [email protected]
KP20ME04                Amprnet:   [email protected]

I get a kernel panic. Similar to

I do not have a recent write down.

I am using a USCC card, which I have been suspecting before. But it seems to be related to either netrom/node disconnects possibly with outstanding frames or tcp/ip started from node, or an DISC/UA at the ax.25 link layer.

I have seen the DISC/UA in listen on a frozen vnc screen before (vnc) tcp retried out and the screen wanished.

Nothing in the logs of the failure, except

Oct 16 21:55:27 pc2 node[650]: sm6tpn @ 213.x.x.x logged in
Oct 16 21:55:45 pc2 node[650]: Connected to VAXJO:SK7HW-5
Oct 17 01:47:21 pc2 syslogd 1.4-0: restart.

suggesting node involved, probably sm6tpn issued a netrom connect.

73
Kjell

RH7.1
Linux pc2 2.4.19 #3 Tue Sep 17 18:33:09 CEST 2002 i586 unknown libax25-devel-0.0.7-7
libax25-0.0.7-7
ax25-tools-0.0.6-13
ax25-apps-0.0.4-9
node-0.3.0-5

I have a been chasing a bug that seems similar lately....
It looks like something goes wrong in sock_def_write_space(). It is called as a result of kfree_skb().
I have been trying to find the cause of it but have been unsuccessfull sofar.
The problem I have is that it only occurs about once a week, so any fix I think I make takes at least a week to test :( unless I find a way to trigger it faster.

Jeroen