a nice way to reboot :-)

a nice way to reboot :-)

[Bruno Cornec]

Hello,

Intrigued by a problem reported by a customer (tar cf /dev/st0 /) and remembering
another issue I had, I tried to investigate a bit and found the following.

On Linux/ia64 when you do cat /proc/kcore, the system just reboots in a couple
of seconds (with RHAS 2.1 std kernel, updated kernel - 2.4.18-e.31) or even with a 
vanilla 2.4.21 + david's patches.
On Linux/i386, no such problem. As I have seen it on zx2000, rx4670, I think it's
not an isolated case. 

Could you confirm on other type of machines ? And more smarter people could even 
probably provide a patch.

Thanks in advance,
Bruno.
-- 
Linux Solution Consultant         Tél: +33 476 143 278 - Fax: +33 476 146 105
HP/Intel Solution Center http://hpintelco.net Hewlett-Packard Grenoble/France
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Re: a nice way to reboot :-)

[Grant Grundler]

On Tue, Jul 22, 2003 at 02:32:54PM +0200, Bruno Cornec wrote:
> On Linux/ia64 when you do cat /proc/kcore, the system just reboots in a couple
> of seconds (with RHAS 2.1 std kernel, updated kernel - 2.4.18-e.31) or even with a 
> vanilla 2.4.21 + david's patches.

Known behavior. David Mosberger tells me Tony Luck changed the support in
2.6 such that only valid regions are accessible. Don't expect it fixed in RHAS
anytime soon. You might check if Bjorn Helgaas' ia64 patch on top of 2.4.21
fixes the same problem.

grant

Re: a nice way to reboot :-)

[Bruno Cornec]

Grant Grundler (iod00d@hp.com) said:

> On Tue, Jul 22, 2003 at 02:32:54PM +0200, Bruno Cornec wrote:
> > On Linux/ia64 when you do cat /proc/kcore, the system just reboots in a couple
> > of seconds (with RHAS 2.1 std kernel, updated kernel - 2.4.18-e.31) or even with a 
> > vanilla 2.4.21 + david's patches.
> 
> Known behavior. 

Humm :-) I tend to find that hardly acceptable that people can crash so easily 
a system. 

> David Mosberger tells me Tony Luck changed the support in
> 2.6 such that only valid regions are accessible. 

I didn't take time to test with a 2.6, but will now that you say it could be useful :-)

> Don't expect it fixed in RHAS
> anytime soon. You might check if Bjorn Helgaas' ia64 patch on top of 2.4.21
> fixes the same problem.

Excuse-me I meant Bjorn's patch on top of 2.4.21. And yes it's crashing the same way
with the latest I tried (linux-2.4.21-ia64-030702.diff.bz2).
Of course, being of no help to provide a valid one, I can't cry if you say
it's not easy/possible on 2.4 ;-)

Thanks for your answer,
Bruno.
-- 
Linux Solution Consultant         Tél: +33 476 143 278 - Fax: +33 476 146 105
HP/Intel Solution Center http://hpintelco.net Hewlett-Packard Grenoble/France
Des infos sur Linux?  http://www.HyPer-Linux.org      http://www.hp.com/linux
La musique ancienne?  http://www.musique-ancienne.org http://www.medieval.org

Re: a nice way to reboot :-)

[Bjorn Helgaas]

On Tuesday 22 July 2003 7:31 am, Bruno Cornec wrote:
> Grant Grundler (iod00d@hp.com) said:
> 
> > On Tue, Jul 22, 2003 at 02:32:54PM +0200, Bruno Cornec wrote:
> > > On Linux/ia64 when you do cat /proc/kcore, the system just reboots in a couple
> > > of seconds (with RHAS 2.1 std kernel, updated kernel - 2.4.18-e.31) or even with a 
> > > vanilla 2.4.21 + david's patches.
> > 
> > Known behavior. 
> 
> Humm :-) I tend to find that hardly acceptable that people can crash so easily 
> a system. 

Believe me, this has been on our list of really annoying things
for a long time.  The fact that this is just one of many ways that
root can crash the box has meant that it hasn't made it to the
top of the list (yet).  It'll be there soon, though...

Bjorn

RE: a nice way to reboot :-)

[digiovanni, lucio]

Unfortunately I tried it on a DELL 3250 (Dual Itanium 2) running RH AS 2.1
updated to 2.4.18-e.31smp and also got a reboot!

-----Original Message-----
From: Bruno Cornec [mailto:Bruno.Cornec@hp.com]
Sent: Tuesday, July 22, 2003 8:33 AM
To: ia64-list
Cc: giovanni_pala@hp.com
Subject: a nice way to reboot :-)


Hello,

Intrigued by a problem reported by a customer (tar cf /dev/st0 /) and
remembering
another issue I had, I tried to investigate a bit and found the following.

On Linux/ia64 when you do cat /proc/kcore, the system just reboots in a
couple
of seconds (with RHAS 2.1 std kernel, updated kernel - 2.4.18-e.31) or even
with a 
vanilla 2.4.21 + david's patches.
On Linux/i386, no such problem. As I have seen it on zx2000, rx4670, I think
it's
not an isolated case. 

Could you confirm on other type of machines ? And more smarter people could
even 
probably provide a patch.

Thanks in advance,
Bruno.
-- 
Linux Solution Consultant         Tél: +33 476 143 278 - Fax: +33 476 146
105
HP/Intel Solution Center http://hpintelco.net Hewlett-Packard
Grenoble/France
Des infos sur Linux?  http://www.HyPer-Linux.org
http://www.hp.com/linux
La musique ancienne?  http://www.musique-ancienne.org
http://www.medieval.org
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Re: a nice way to reboot :-)

[Matthew Wilcox]

On Tue, Jul 22, 2003 at 03:31:33PM +0200, Bruno Cornec wrote:
> Humm :-) I tend to find that hardly acceptable that people can crash so easily 
> a system. 

it's true on other architectures too, not just ia64.  root can crash
the system any way they want.  stupid user syndrome; they should be
using -xdev to not tar up /proc.

-- 
"It's not Hollywood.  War is real, war is primarily not about defeat or
victory, it is about death.  I've seen thousands and thousands of dead bodies.
Do you think I want to have an academic debate on this subject?" -- Robert Fisk

Re: a nice way to reboot :-)

[Bruno Cornec]

Matthew Wilcox (willy@debian.org) said:

> it's true on other architectures too, not just ia64.  

Well in general yes, but at least on i386 (I can't test on something else)
doing cat /proc/kcore doesn't crash the system. And BTW why should it ?
There is nothing wrong with it (for ex. I used it a lot of times to try
to find a BIOS revision on i386).

I just wonder if this could be used as a DOS from outside the system. In
which case, it would be a Bad Thing (tm :-)

> root can crash
> the system any way they want.  

Yes, that's true. But it just more surprising when you think you just
pass a normal command ;-)

> stupid user syndrome; they should be
> using -xdev to not tar up /proc.

Yes, of course, I again agree with you. 
But even if I don't do that myself, I tried on a rx5670 the cat /proc/kcore
in the past, with the same result, for valid (IMHO) reasons and was really
surprised to see the system rebooting. BTW, it also underline the inability
for Oracle 9iRAC to fail over properly, which was also a surprise :-)

Every time I see a program doing "core dumped" even if I pass to it crazy
args, I tend to believe it's not good enough, and can hide other problems.
It's a bug for me, not a feature.
And again in that precise case, I'm far from being able to provide patch.
Just grumbling ;-)

Bruno.
-- 
Linux Solution Consultant         Tél: +33 476 143 278 - Fax: +33 476 146 105
HP/Intel Solution Center http://hpintelco.net Hewlett-Packard Grenoble/France
Des infos sur Linux?  http://www.HyPer-Linux.org      http://www.hp.com/linux
La musique ancienne?  http://www.musique-ancienne.org http://www.medieval.org

Re: a nice way to reboot :-)

[Andreas Schwab]

Bruno Cornec <Bruno.Cornec@hp.com> writes:

|> I just wonder if this could be used as a DOS from outside the system. In
|> which case, it would be a Bad Thing (tm :-)
|> 
|> > root can crash
|> > the system any way they want.  
|> 
|> Yes, that's true. But it just more surprising when you think you just
|> pass a normal command ;-)

If you are already root then shutdown -h is just as effective.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux AG, Deutschherrnstr. 15-19, D-90429 Nürnberg
Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: a nice way to reboot :-)

[Matthew Wilcox]

On Thu, Jul 24, 2003 at 02:30:51PM +0200, Bruno Cornec wrote:
> Well in general yes, but at least on i386 (I can't test on something else)
> doing cat /proc/kcore doesn't crash the system. And BTW why should it ?
> There is nothing wrong with it (for ex. I used it a lot of times to try
> to find a BIOS revision on i386).

you should be using gdb on /proc/kcore; nothing else.

> I just wonder if this could be used as a DOS from outside the system. In
> which case, it would be a Bad Thing (tm :-)

$ ls -l /proc/kcore 
-r--------    1 root     root     167776256 2003-07-24 08:46 /proc/kcore

and if they're root, you're already fucked.

-- 
"It's not Hollywood.  War is real, war is primarily not about defeat or
victory, it is about death.  I've seen thousands and thousands of dead bodies.
Do you think I want to have an academic debate on this subject?" -- Robert Fisk

RE: a nice way to reboot :-)

[Van Maren, Kevin]

I think we've beaten this to death: yes, it is an annoying bug, and
deserves to be fixed.

Just to clarify: I think you want to use tar with --exclude=/proc or -l;
tar doesn't have an -xdev option (that is for find, used with cpio).
I've also used --exclude-from=/nodump where /nodump lists the
directories to skip: /tmp, /proc, /dev, etc.  I actually started
doing that because my IA64 Linux system rebooted when using tar to
backup (several filesystems at once) to tape :-(
Also note that those are GNU tar extension, and are not available
on SysV (but then, I've never seen a SVR4 machine reboot reading /proc).

Andreas, I don't think your analogy is even close: tar is documented
create an archive; shutdown is documented to reboot the system:
what Bruno was saying is that running tar (even on /proc) is no more
expected to reboot the system than doing an "ls" on /proc.
The UnitedLinux man page for tar makes no indication that root can
reboot the system with it...  Even worse, this behavior does not
occur on other Linux/BSD systems, so people don't have a "reasonable
expectation" for it to kill the system, especially when "properly"
invoked.  (Now, trying to extract an old /proc from a tarfile is
different -- I'll believe that attempting to replace /proc could
reasonably be expected to cause problems, but not reading /proc).

Kevin

-----Original Message-----
From: Andreas Schwab [mailto:schwab@suse.de]
Sent: Thursday, July 24, 2003 6:52 AM
To: Bruno Cornec
Cc: Matthew Wilcox; ia64-list; giovanni_pala@hp.com
Subject: Re: a nice way to reboot :-)


Bruno Cornec <Bruno.Cornec@hp.com> writes:

|> I just wonder if this could be used as a DOS from outside the system. In
|> which case, it would be a Bad Thing (tm :-)
|> 
|> > root can crash
|> > the system any way they want.  
|> 
|> Yes, that's true. But it just more surprising when you think you just
|> pass a normal command ;-)

If you are already root then shutdown -h is just as effective.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux AG, Deutschherrnstr. 15-19, D-90429 Nürnberg
Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."
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