Date: Wed, 27 Feb 2008 21:00:53 -0600
From: serge@hallyn.com
To: BuraphaLinux Server <buraphalinuxserver@gmail.com>
Cc: serge@hallyn.com, linux-kernel@vger.kernel.org
Subject: Re: at program breaks with kernel 2.6.24
Message-ID: <20080228030053.GA25033@vino.hallyn.com>
References: <5d75f4610802270427y789ffae9ie2682059206eed51@mail.gmail.com> <20080227181740.GA14532@vino.hallyn.com> <5d75f4610802271147m77d3b3e3r4d01ecf3740a7dbb@mail.gmail.com>
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Quoting BuraphaLinux Server (buraphalinuxserver@gmail.com):
> This is gmail which has broken line wrapping I cannot fix. Anyway, I
> did build the new kernel but it still does not work for me. I tried to
> strace, but that didn't work for me either. This is as a non-root user
> (and same 'at'/'atd' binaries work on 2.6.23.X):
> 
> bash-3.2$ at now
> warning: commands will be executed using /bin/sh
> at> echo "suid is busted"
> at> <EOT>
> job 4 at Thu Feb 28 02:16:00 2008
> Can't signal atd (permission denied)
> bash-3.2$ ls -ld $(which at)
> -rws--x--x 1 daemon daemon 36468 Jan 11 15:37 /usr/bin/at
> bash-3.2$ ps -ef | grep atd
> daemon 2874 1 0 02:14 ? 00:00:00 /usr/sbin/atd -b 15 -l 1
> bozo 3054 3049 0 02:16 pts/0 00:00:00 grep atd
> bash-3.2$ ls -ld /var/spool/at*
> drwxrwxrwt 2 daemon daemon 4096 Feb 28 02:16 /var/spool/atjobs
> drwx------ 2 daemon daemon 4096 Feb 27 20:02 /var/spool/atspool
> bash-3.2$ uname -a
> Linux zappaman.cs.buu.ac.th 2.6.25-rc3 #1 SMP Thu Feb 28 01:29:46 ICT
> 2008 i686 pentium4 i386 GNU/Linux
> bash-3.2$ strace -s 99999 -v -o /tmp/pain at now
> warning: commands will be executed using /bin/sh
> Cannot open lockfile /var/spool/atjobs/.SEQ: Permission denied
> bash-3.2$ at now
> warning: commands will be executed using /bin/sh
> at> echo "hi"
> at> <EOT>
> job 7 at Thu Feb 28 02:19:00 2008
> Can't signal atd (permission denied)
> 
> My kenrel .config is big, so it is attached so I don't get any cut and
> paste error.
> 
> On 2/28/08, serge@hallyn.com <serge@hallyn.com> wrote:
> > Quoting BuraphaLinux Server (buraphalinuxserver@gmail.com):
> > > http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=463669
> > >
> > > I have the same problem - it is not debian specific. Did the
> > > semantics of kill() change with the new kernel? I thought as long as
> > > something is setuid, even with capability stuff around the setuid
> > > programs just get _all_ capabilities and would keep working.
> > >
> > > I did a good search and found many people with the problem, but no
> > > solutions except going back to 2.6.23.x kernels. I guess you'll flame
> > > me, but at least include a link to the solution too.
> >
> > Why would we flame you?
> 
> Because maybe I'm doing something stupid and didn't patch/rebuild
> something when changing kernels like I should.  I haven't had trouble
> with at for many years of kernel changes, but 2.6.24 was the first
> with the new security stuff and maybe I need to have some
> capability-aware 'at' program?
> 
> >                                          I'll just apologize as I think it's my fault,
> > and ask you to please try the newest available kernel where I believe it
> > should be fixed.
> 
> Do I need to recompile glibc and the at software to adjust so some
> kernel interface changes?  Did the 'make oldconfig' generate some bad
> config combination?  As root it works, so I don't think the at or atd
> are broken (but maybe they have to be patched for >2.6.23.X ?)
> 
> bash-3.2$ su - root
> Password:
> BLS #at now
> warning: commands will be executed using /bin/sh
> at> echo "uh-huh..."
> at> <EOT>
> job 8 at Thu Feb 28 02:30:00 2008
> 
> (and I checked and the job completes normally)
> 
> > thanks,
> > -serge
> 
> Thank you for reading.  Any ideas on what to try next?

I'm working on setting up something I can test this on better, but just
for good measure can you try the following patch?  It should simply
prevent the extra signal checks from happening.

thanks,
-serge

>From f48d28fe525652cb7321d5f545f9dcdfb3ce97d8 Mon Sep 17 00:00:00 2001
From: Serge Hallyn <serge@hallyn.com>
Date: Wed, 27 Feb 2008 20:53:47 +0000
Subject: [PATCH 1/1] file capabilities: get rid of cap_task_kill

This is just a test to not use cap_task_kill.  We will see whether
this fixes the atd problem

Signed-off-by: Serge Hallyn <serge@hallyn.com>
---
 include/linux/security.h |    2 +-
 security/capability.c    |    1 -
 2 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/include/linux/security.h b/include/linux/security.h
index fe52cde..4c43914 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -2138,7 +2138,7 @@ static inline int security_task_kill (struct task_struct *p,
 				      struct siginfo *info, int sig,
 				      u32 secid)
 {
-	return cap_task_kill(p, info, sig, secid);
+	return 0;
 }
 
 static inline int security_task_wait (struct task_struct *p)
diff --git a/security/capability.c b/security/capability.c
index 9e99f36..2c6e06d 100644
--- a/security/capability.c
+++ b/security/capability.c
@@ -40,7 +40,6 @@ static struct security_operations capability_ops = {
 	.inode_need_killpriv =		cap_inode_need_killpriv,
 	.inode_killpriv =		cap_inode_killpriv,
 
-	.task_kill =			cap_task_kill,
 	.task_setscheduler =		cap_task_setscheduler,
 	.task_setioprio =		cap_task_setioprio,
 	.task_setnice =			cap_task_setnice,
-- 
1.5.2.5


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