linux-kernel - Re: [PATCH] Change task

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Message-ID: <20140310202155.GR16640@madcap2.tricolour.ca>
Date:	Mon, 10 Mar 2014 16:21:55 -0400
From:	Richard Guy Briggs <rgb@...hat.com>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	peterz@...radead.org, paulmck@...ux.vnet.ibm.com,
	laijs@...fujitsu.com, akpm@...ux-foundation.org, joe@...ches.com,
	keescook@...omium.org, geert@...ux-m68k.org, jkosina@...e.cz,
	viro@...iv.linux.org.uk, davem@...emloft.net,
	linux-kernel@...r.kernel.org, mingo@...e.hu, rostedt@...dmis.org,
	tglx@...utronix.de, linux-security-module@...r.kernel.org
Subject: Re: [PATCH] Change task_struct->comm to use RCU.

On 14/03/08, Tetsuo Handa wrote:
> Richard Guy Briggs wrote:
> > > > >   Likewise, audit_log_untrustedstring(ab, current->comm) is racy.
> > > > >   If task->comm was "Hello Linux" until audit_string_contains_control() in
> > > > >   audit_log_n_untrustedstring() returns false, and becomes "Penguin" before
> > > > >   memcpy() in audit_log_n_string() is called, memcpy() will emit "Penguin\0nux"
> > > > >   into the audit log, which results in loss of information (e.g. SELinux
> > > > >   context) due to the unexpected '\0' byte.
> > > > 
> > > > I expect the audit people don't like this? Also, how do audit and the
> > > > LSM crap things interact? I thought they were both different piles of
> > > > ignorable goo?
> > > 
> > > I think the audit people do not like loss of information. Some of LSM modules
> > > are using audit subsystem for recording security related events. An example is
> > > shown later.
> > 
> > This is true, however since comm it untrusted because it can be modified
> > by the user audit doesn't trust it anyways, so who cares?
> 
> Excuse me, but did you understand this side effect correctly?

<snip>

> ), you can see that fields after comm= (e.g. exe= subj= key= ) are missing.

Ok, from your desciption and example I had clearly not fully understood
the problem.

> ---------- An audit log with race ----------
> type=SYSCALL msg=audit(1394281498.566:63): arch=40000003 syscall=11 success=yes exit=0 a0=858c9c8 a1=85a6620 a2=858e4a0 a3=85a6620 items=2 ppid=1747 pid=2662 auid=0 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=pts1 ses=2 comm="truncated
> type=EXECVE msg=audit(1394281498.566:63): argc=1 a0="/tmp/printable-comm"
> type=CWD msg=audit(1394281498.566:63):  cwd="/root"
> type=PATH msg=audit(1394281498.566:63): item=0 name="/tmp/printable-comm" inode=1970955 dev=08:01 mode=0100755 ouid=0 ogid=0 rdev=00:00 obj=system_u:object_r:bin_t:s0 nametype=NORMAL
> type=PATH msg=audit(1394281498.566:63): item=1 name=(null) inode=2360187 dev=08:01 mode=0100755 ouid=0 ogid=0 rdev=00:00 obj=system_u:object_r:ld_so_t:s0 nametype=NORMAL
> ---------- An audit log with race ----------
> 
> Even if you don't trust the comm= field, it is annoying for me that fields
> after comm= are missing in the audit log.

More than annoying, that isn't acceptable.

- RGB

--
Richard Guy Briggs <rbriggs@...hat.com>
Senior Software Engineer, Kernel Security, AMER ENG Base Operating Systems, Red Hat
Remote, Ottawa, Canada
Voice: +1.647.777.2635, Internal: (81) 32635, Alt: +1.613.693.0684x3545
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