linux-kernel - Re: [PATCH] sys: Fix missing rcu protection for sys

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Message-ID: <20100212142239.GA9653@us.ibm.com>
Date:	Fri, 12 Feb 2010 08:22:39 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	oleg@...hat.com, tglx@...utronix.de, linux-kernel@...r.kernel.org,
	paulmck@...ux.vnet.ibm.com, dipankar@...ibm.com, mingo@...e.hu,
	peterz@...radead.org, viro@...iv.linux.org.uk, jmorris@...ei.org,
	dhowells@...hat.com, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH] sys: Fix missing rcu protection for sys_getpriority.

Quoting Tetsuo Handa (penguin-kernel@...ove.SAKURA.ne.jp):
> Oleg Nesterov wrote:
> > This also fixes another bug here. find_task_by_vpid() is not safe
> > without rcu_read_lock(). I do not mean it is not safe to use the
> > result, just find_pid_ns() by itself is not safe.
> > 
> > Usually tasklist gives enough protection, but if copy_process() fails
> > it calls free_pid() lockless and does call_rcu(delayed_put_pid().
> > This means, without rcu lock find_pid_ns() can't scan the hash table
> > safely.
> 
> This bug for sys_setpriority() was fixed, but not fixed for sys_getpriority().
> Why not to add it as well?
> --------------------
> [PATCH] sys: Fix missing rcu protection for sys_setpriority.
> 
> find_task_by_vpid() is not safe without rcu_read_lock().
> 2.6.33-rc7 got RCU protection for sys_setpriority() but missed it for
> sys_getpriority().
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>

Would be needed indeed but I don't have a copy of linux-next handy -
if this isn't changed there yet then

Acked-by: Serge Hallyn <serue@...ibm.com>

thanks,
-serge

> ---
>  kernel/sys.c |    2 ++
>  1 file changed, 2 insertions(+)
> 
> --- linux-2.6.33-rc7.orig/kernel/sys.c
> +++ linux-2.6.33-rc7/kernel/sys.c
> @@ -222,6 +222,7 @@ SYSCALL_DEFINE2(getpriority, int, which,
>  	if (which > PRIO_USER || which < PRIO_PROCESS)
>  		return -EINVAL;
> 
> +	rcu_read_lock();
>  	read_lock(&tasklist_lock);
>  	switch (which) {
>  		case PRIO_PROCESS:
> @@ -267,6 +268,7 @@ SYSCALL_DEFINE2(getpriority, int, which,
>  	}
>  out_unlock:
>  	read_unlock(&tasklist_lock);
> +	rcu_read_unlock();
> 
>  	return retval;
>  }
> --
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