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Subject[2.1.131] Help me fix this PPP panic
Hello,

There is a serious bug in 2.1.1XX. I have seen it, and others have
as well. Both myself and the other few that have reported it are running
Alpha's... But don't tune out yet!

The bug is that the PPP driver is passing bad lengths to skb_put, which is
in turn panicking the kernel. Because current == task[0], we get to play
with e2fsck on restart. ;(

In my case, I get kernel panics very often, anywhere between a few minutes
to a few days of uptime. Fortunately, the address was consistant with
every panic, so I rebuilt my kernel with -g and waited... I seem to be
able to bait it on by ripping audio tracks off my SCSI CDROM, or playing
.WAV files. Weird.. Anyway, here is what gdb has to say:

(bryan/root.2@earth) ~/linux % gdb -c /proc/kcore vmlinux
GNU gdb 981029
Copyright 1998 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you
are
welcome to change it and/or distribute copies of it under certain
conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "show warranty" for details.
This GDB was configured as "alpha-redhat-linux"...
#0 0x0 in ?? ()
(gdb) l *0xfffffc000041a060
0xfffffc000041a060 is in rcv_proto_vjc_comp (ppp.c:2051).
2046 printk(KERN_NOTICE
2047 "ppp: error in VJ decompression\n");
2048 return 0;
2049 }
2050 skb_put(skb, new_count + PPP_HDRLEN - skb->len);
2051 return rcv_proto_ip(ppp, skb);
2052 }
2053
2054 /*
2055 * Process the receipt of an VJ Un-compressed frame
(gdb) q

Now I need to fix this bastard bug, because I've already had a great deal
of downtime and trashed files because of it. :( Is anyone willing to help,
and how should I procede? For now I'm just going to add a check on the
length before the skb_put and toss the packet if it's too big. I'll add a
printk giving me some information on the packet.

thanks,
-bp
--
B. James Phillippe . bryan@terran.org
Linux Engineer/Admin . http://www.terran.org/~bryan
Member since 1.1.59 . finger:bryan@earth.terran.org


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