Red Hat Bugzilla – Bug 231850
PPP causes a kernel crash
Last modified: 2008-04-10 14:49:25 EDT
Description of problem:
We've found a replicable situation where pppd causes a kernel crash. First of
all a bit of framework.
We use pppd to provide remote support to some of our customers. Every customer
has a personal account to connect to our server using PPP. The firewall on
these accounts is configured so that we can connect back to their servers and
check for problems, but the remote server has basicly no access at all to our
Since few weeks one of these customers caught a virus or a dialer (it uses a
windows based server) which tries to connect to our server using the RAS entry
configured for remote support, probably thinking it is an Internet connection.
The RAS entry has the password saved, so that the virus is able to authenticate
against our server, even though it isn't able to do anything else because of
the configured firewall.
So far nothing wrong, by the way sometimes the virus is able to bring our
server down because of a kernel crash. I haven't been able to save the kernel
OOPS on screen but it clearly reported that the problem was caused by ppp. I
have a log of the debug PPP session as saved by pppd (see attachemnt). We will
further investigate to try to identify the virus or the dialer and may be catch
the kernel OOPS.
Version-Release number of selected component (if applicable): ppp 2.4.3-6.2.1,
kernel-smp 2.6.17 1.2157_FC5
How reproducible: difficult to reproduce
Steps to Reproduce: you need an infected windows pc, more info to be gathered
Actual results: kernel crash
Expected results: normal connection but no kernel crash and everything filtered
out by the firewall
Additional info: none
Assigning to kernel.
Some news. The problem happened again. In the meantime I upgraded the kernel to
the latest fc5 one:
Name : kernel-smp
Version : 2.6.19
Release : 1.2288.2.4.fc5
This time I captured part of the kernel OOPS. Unfortunately I had to copy it
manually from the screen and I couldn't copy it completely because I had to
restart the server ASAP. I hope I've copied the relevant parts and I didn't
some mistake while copying:
EIP is at skb_under_panic+0x59/0x67
Process ksoftirqd/1 (pid 6, ti=c07a5000 task=dff210f0 task.ti=dff2a000)
[<e0bdd915>] ppp_receive_nommp_frame+0x537/x6a6 [ppp_generic]
[<e0bbe4d8>] ppp_input+0xbc/0xeb [ppp_generic]
[<e0bc5a68>] ppp_async_process+0x26/0x59 [ppp_async]
EIP: [<c05bc5bb>] skb_under_panic+0x59/0x67 SS:ESP 0068::c07a5f54
<0> Kernel panic - not syncing: fatal exception in interrupt
This is a kernel problem, assigning to kernel.
latest FC5 kernel is 2.6.20-1.2300.fc5, released March 14th.
Please test with that.
Upgraded to 2.6.20, waiting to see what happens.
Side note: while upgrading I discovered another unrelated problem, see bug
Patch is now available, will be in next update.
*** Bug 231853 has been marked as a duplicate of this bug. ***
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The process we are following is outlined here:
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I didn't do further tests for this issue, nevertheless the problem never
happened again. There have been various kernel upgrades since this bug, which
makes me think that it has been fixed in newer kernels.
Thanks for the update.