From: john stultz <johnstul@us.ibm.com>
To: Joe Perches <joe@perches.com>
Cc: LKML <linux-kernel@vger.kernel.org>, "Ted Ts'o" <tytso@mit.edu>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
David Rientjes <rientjes@google.com>,
Dave Hansen <dave@linux.vnet.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org
Subject: Re: [PATCH 2/3] printk: Add %ptc to safely print a task's comm
Date: Tue, 10 May 2011 18:16:01 -0700 [thread overview]
Message-ID: <1305076561.2939.72.camel@work-vm> (raw)
In-Reply-To: <1305076246.2939.67.camel@work-vm>
On Tue, 2011-05-10 at 18:10 -0700, John Stultz wrote:
> On Tue, 2011-05-10 at 17:51 -0700, Joe Perches wrote:
> > Could misuse of %ptc (not using current) cause system lockup?
>
> It very well could. Although I don't see other %p options tring to
> handle invalid pointers. Any suggestions on how to best handle this?
And just to clarify on this point, I'm responding to if a invalid
pointer was provided, causing the dereference to go awry.
If a valid non-current task was provided, the locking should be ok as we
disable irqs while the write_seqlock is held in set_task_comm().
The only places this could cause a problem was if you tried to printk
with a %ptc while holding the task->comm_lock. However, the lock is only
shortly held in task_comm_string, and get_task_comm and set_task_comm.
So it is fairly easy to audit for correctness.
If there is some other situation you had in mind, please let me know.
thanks
-john
WARNING: multiple messages have this Message-ID (diff)
From: john stultz <johnstul@us.ibm.com>
To: Joe Perches <joe@perches.com>
Cc: LKML <linux-kernel@vger.kernel.org>, Ted Ts'o <tytso@mit.edu>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
David Rientjes <rientjes@google.com>,
Dave Hansen <dave@linux.vnet.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org
Subject: Re: [PATCH 2/3] printk: Add %ptc to safely print a task's comm
Date: Tue, 10 May 2011 18:16:01 -0700 [thread overview]
Message-ID: <1305076561.2939.72.camel@work-vm> (raw)
In-Reply-To: <1305076246.2939.67.camel@work-vm>
On Tue, 2011-05-10 at 18:10 -0700, John Stultz wrote:
> On Tue, 2011-05-10 at 17:51 -0700, Joe Perches wrote:
> > Could misuse of %ptc (not using current) cause system lockup?
>
> It very well could. Although I don't see other %p options tring to
> handle invalid pointers. Any suggestions on how to best handle this?
And just to clarify on this point, I'm responding to if a invalid
pointer was provided, causing the dereference to go awry.
If a valid non-current task was provided, the locking should be ok as we
disable irqs while the write_seqlock is held in set_task_comm().
The only places this could cause a problem was if you tried to printk
with a %ptc while holding the task->comm_lock. However, the lock is only
shortly held in task_comm_string, and get_task_comm and set_task_comm.
So it is fairly easy to audit for correctness.
If there is some other situation you had in mind, please let me know.
thanks
-john
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next prev parent reply other threads:[~2011-05-11 1:16 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-11 0:23 [RFC][PATCH 0/3] v2 Improve task->comm locking situation John Stultz
2011-05-11 0:23 ` John Stultz
2011-05-11 0:23 ` [PATCH 1/3] comm: Introduce comm_lock seqlock to protect task->comm access John Stultz
2011-05-11 0:23 ` John Stultz
2011-05-11 17:39 ` Andi Kleen
2011-05-11 17:39 ` Andi Kleen
2011-05-12 22:00 ` David Rientjes
2011-05-12 22:00 ` David Rientjes
2011-05-11 0:23 ` [PATCH 2/3] printk: Add %ptc to safely print a task's comm John Stultz
2011-05-11 0:23 ` John Stultz
2011-05-11 0:51 ` Joe Perches
2011-05-11 0:51 ` Joe Perches
2011-05-11 1:10 ` John Stultz
2011-05-11 1:10 ` John Stultz
2011-05-11 1:16 ` john stultz [this message]
2011-05-11 1:16 ` john stultz
2011-05-11 1:20 ` Joe Perches
2011-05-11 1:20 ` Joe Perches
2011-05-12 22:12 ` David Rientjes
2011-05-12 22:12 ` David Rientjes
2011-05-12 22:29 ` Joe Perches
2011-05-12 22:29 ` Joe Perches
2011-05-13 21:56 ` David Rientjes
2011-05-13 21:56 ` David Rientjes
2011-05-12 22:10 ` David Rientjes
2011-05-12 22:10 ` David Rientjes
2011-05-11 9:33 ` Américo Wang
2011-05-11 9:33 ` Américo Wang
2011-05-11 21:02 ` John Stultz
2011-05-11 21:02 ` John Stultz
2011-05-12 10:43 ` Américo Wang
2011-05-12 10:43 ` Américo Wang
2011-05-12 10:45 ` Américo Wang
2011-05-12 10:45 ` Américo Wang
2011-05-12 18:01 ` John Stultz
2011-05-12 18:01 ` John Stultz
2011-05-11 17:36 ` Andi Kleen
2011-05-11 17:36 ` Andi Kleen
2011-05-11 21:04 ` John Stultz
2011-05-11 21:04 ` John Stultz
2011-05-11 0:23 ` [PATCH 3/3] comm: ext4: Protect task->comm access by using %ptc John Stultz
2011-05-11 0:23 ` John Stultz
2011-05-12 22:14 ` David Rientjes
2011-05-12 22:14 ` David Rientjes
2011-05-12 22:29 ` John Stultz
2011-05-12 22:29 ` John Stultz
2011-05-12 22:34 ` Andrew Morton
2011-05-12 22:34 ` Andrew Morton
-- strict thread matches above, loose matches on Subject: below --
2011-05-12 23:02 [PATCH 0/3] v3 Improve task->comm locking situation John Stultz
2011-05-12 23:02 ` [PATCH 2/3] printk: Add %ptc to safely print a task's comm John Stultz
2011-05-12 23:02 ` John Stultz
2011-05-16 21:19 [PATCH 0/3] v4 Improve task->comm locking situation John Stultz
2011-05-16 21:19 ` [PATCH 2/3] printk: Add %ptc to safely print a task's comm John Stultz
2011-05-16 21:19 ` John Stultz
2011-05-16 21:54 ` Jiri Slaby
2011-05-16 21:54 ` Jiri Slaby
2011-05-16 23:10 ` John Stultz
2011-05-16 23:10 ` John Stultz
2011-05-16 23:56 ` Joe Perches
2011-05-16 23:56 ` Joe Perches
2011-05-17 0:11 ` John Stultz
2011-05-17 0:11 ` John Stultz
2011-05-17 7:21 ` Jiri Slaby
2011-05-17 7:21 ` Jiri Slaby
2011-05-18 0:32 ` KOSAKI Motohiro
2011-05-18 0:32 ` KOSAKI Motohiro
2011-05-17 20:47 [PATCH 0/3] v5 Improve task->comm locking situation John Stultz
2011-05-17 20:47 ` [PATCH 2/3] printk: Add %ptc to safely print a task's comm John Stultz
2011-05-17 20:47 ` John Stultz
2011-05-17 21:42 ` Jiri Slaby
2011-05-17 21:42 ` Jiri Slaby
2011-05-17 21:52 ` Joe Perches
2011-05-17 21:52 ` Joe Perches
2011-05-17 22:04 ` Jiri Slaby
2011-05-17 22:04 ` Jiri Slaby
2011-05-17 22:17 ` Joe Perches
2011-05-17 22:17 ` Joe Perches
2011-05-17 22:17 ` John Stultz
2011-05-17 22:17 ` John Stultz
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