From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: John Stultz <john.stultz@linaro.org>
Cc: LKML <linux-kernel@vger.kernel.org>, "Ted Ts'o" <tytso@mit.edu>,
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 1/3] comm: Introduce comm_lock seqlock to protect task->comm access
Date: Fri, 13 May 2011 20:13:26 +0900 [thread overview]
Message-ID: <4DCD1256.4070808@jp.fujitsu.com> (raw)
In-Reply-To: <1305241371-25276-2-git-send-email-john.stultz@linaro.org>
Hi
Sorry for the long delay.
> char *get_task_comm(char *buf, struct task_struct *tsk)
> {
> - /* buf must be at least sizeof(tsk->comm) in size */
> - task_lock(tsk);
> - strncpy(buf, tsk->comm, sizeof(tsk->comm));
> - task_unlock(tsk);
> + unsigned long seq;
> +
> + do {
> + seq = read_seqbegin(&tsk->comm_lock);
> +
> + strncpy(buf, tsk->comm, sizeof(tsk->comm));
> +
> + } while (read_seqretry(&tsk->comm_lock, seq));
> +
> return buf;
> }
Can you please explain why we should use seqlock? That said,
we didn't use seqlock for /proc items. because, plenty seqlock
write may makes readers busy wait. Then, if we don't have another
protection, we give the local DoS attack way to attackers.
task->comm is used for very fundamentally. then, I doubt we can
assume write is enough rare. Why can't we use normal spinlock?
WARNING: multiple messages have this Message-ID (diff)
From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: John Stultz <john.stultz@linaro.org>
Cc: LKML <linux-kernel@vger.kernel.org>, Ted Ts'o <tytso@mit.edu>,
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 1/3] comm: Introduce comm_lock seqlock to protect task->comm access
Date: Fri, 13 May 2011 20:13:26 +0900 [thread overview]
Message-ID: <4DCD1256.4070808@jp.fujitsu.com> (raw)
In-Reply-To: <1305241371-25276-2-git-send-email-john.stultz@linaro.org>
Hi
Sorry for the long delay.
> char *get_task_comm(char *buf, struct task_struct *tsk)
> {
> - /* buf must be at least sizeof(tsk->comm) in size */
> - task_lock(tsk);
> - strncpy(buf, tsk->comm, sizeof(tsk->comm));
> - task_unlock(tsk);
> + unsigned long seq;
> +
> + do {
> + seq = read_seqbegin(&tsk->comm_lock);
> +
> + strncpy(buf, tsk->comm, sizeof(tsk->comm));
> +
> + } while (read_seqretry(&tsk->comm_lock, seq));
> +
> return buf;
> }
Can you please explain why we should use seqlock? That said,
we didn't use seqlock for /proc items. because, plenty seqlock
write may makes readers busy wait. Then, if we don't have another
protection, we give the local DoS attack way to attackers.
task->comm is used for very fundamentally. then, I doubt we can
assume write is enough rare. Why can't we use normal spinlock?
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next prev parent reply other threads:[~2011-05-13 11:11 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-12 23:02 [PATCH 0/3] v3 Improve task->comm locking situation John Stultz
2011-05-12 23:02 ` John Stultz
2011-05-12 23:02 ` [PATCH 1/3] comm: Introduce comm_lock seqlock to protect task->comm access John Stultz
2011-05-12 23:02 ` John Stultz
2011-05-13 11:13 ` KOSAKI Motohiro [this message]
2011-05-13 11:13 ` KOSAKI Motohiro
2011-05-13 18:27 ` John Stultz
2011-05-13 18:27 ` John Stultz
2011-05-14 11:12 ` KOSAKI Motohiro
2011-05-14 11:12 ` KOSAKI Motohiro
2011-05-16 20:34 ` John Stultz
2011-05-16 20:34 ` 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
2011-05-12 23:02 ` [PATCH 3/3] checkpatch.pl: Add check for current->comm references John Stultz
2011-05-12 23:02 ` John Stultz
2011-05-13 6:33 ` Jiri Slaby
2011-05-13 6:33 ` Jiri Slaby
2011-05-13 11:02 ` Michal Nazarewicz
2011-05-13 11:02 ` Michal Nazarewicz
2011-05-16 21:23 ` David Rientjes
2011-05-16 21:23 ` David Rientjes
2011-05-13 11:13 ` KOSAKI Motohiro
2011-05-13 11:13 ` KOSAKI Motohiro
2011-05-13 18:28 ` John Stultz
2011-05-13 18:28 ` John Stultz
-- strict thread matches above, loose matches on Subject: below --
2011-05-16 21:19 [PATCH 0/3] v4 Improve task->comm locking situation John Stultz
2011-05-16 21:19 ` [PATCH 1/3] comm: Introduce comm_lock seqlock to protect task->comm access John Stultz
2011-05-16 21:19 ` John Stultz
2011-05-16 22:01 ` Jiri Slaby
2011-05-16 22:01 ` Jiri Slaby
2011-05-17 1:47 ` John Stultz
2011-05-17 1:47 ` John Stultz
2011-05-18 0:28 ` KOSAKI Motohiro
2011-05-18 0:28 ` KOSAKI Motohiro
2011-05-11 0:23 [RFC][PATCH 0/3] v2 Improve task->comm locking situation 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
2011-04-28 4:03 [RFC][PATCH 0/3] Improve task->comm locking situation John Stultz
2011-04-28 4:03 ` [PATCH 1/3] comm: Introduce comm_lock seqlock to protect task->comm access John Stultz
2011-04-28 4:03 ` John Stultz
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