linux-kernel - Re: [PATCH 3/2 -v3] fcntl: F_[SG]ETOWN

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Date:	Tue, 04 Aug 2009 18:52:43 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, eranian@...il.com,
	mingo@...e.hu, linux-kernel@...r.kernel.org, tglx@...utronix.de,
	robert.richter@....com, paulus@...ba.org, andi@...stfloor.org,
	mpjohn@...ibm.com, cel@...ibm.com, cjashfor@...ibm.com,
	mucci@...s.utk.edu, terpstra@...s.utk.edu,
	perfmon2-devel@...ts.sourceforge.net, mtk.manpages@...glemail.com,
	roland@...hat.com
Subject: Re: [PATCH 3/2 -v3] fcntl: F_[SG]ETOWN_EX

On Tue, 2009-08-04 at 18:20 +0200, Oleg Nesterov wrote:
> On 08/04, Peter Zijlstra wrote:
> >
> > +static int f_setown_ex(struct file *filp, unsigned long arg)
> > +{
> > +	struct f_owner_ex * __user owner_p = (void * __user)arg;
> > +	struct f_owner_ex owner;
> > +	struct pid *pid;
> > +	int type;
> > +	int ret;
> > +
> > +	ret = copy_from_user(&owner, owner_p, sizeof(owner));
> > +	if (ret)
> > +		return ret;
> > +
> > +	switch (owner.type) {
> > +	case F_OWNER_TID:
> > +		type = PIDTYPE_MAX;
> > +		break;
> > +
> > +	case F_OWNER_PID:
> > +		type = PIDTYPE_PID;
> > +		break;
> > +
> > +	case F_OWNER_GID:
> > +		type = PIDTYPE_PGID;
> > +		break;
> > +	}
> 
> Note that send_sigio()->do_each_pid_task(type) must use the valid
> type < PIDTYPE_MAX, or we can crash/etc.
> 
> This means f_setown_ex() should be careful with the wrong owner->type,
> the switch() above needs
> 
> 	default:
> 		return -EINVAL;

D'0h very true.

> > +	rcu_read_lock();
> > +	pid = find_vpid(owner.pid);
> > +	ret = __f_setown(filp, pid, type, 1);
> > +	rcu_read_unlock();
> > +
> > +	return ret;
> 
> Perhaps it makes sense to return -ESRCH if owner.pid && !pid, not
> sure.

We'd need that case to unset/clear the owner, so returning -ESRCH might
confuse users I think.

> > @@ -474,16 +540,23 @@ void send_sigio(struct fown_struct *fown
> >  	struct task_struct *p;
> >  	enum pid_type type;
> >  	struct pid *pid;
> > +	int group = 1;
> >  	
> >  	read_lock(&fown->lock);
> > +
> >  	type = fown->pid_type;
> > +	if (type == PIDTYPE_MAX) {
> > +		group = 0;
> > +		type = PIDTYPE_PID;
> > +	}
> 
> And send_sigurg() needs the same change. I am not sure we should teach
> send_sigurg_to_task() to handle the F_OWNER_TID, but we must ensure
> send_sigurg()->do_each_pid_task() won't be called with PIDTYPE_MAX.

How about the below delta, it changes send_sigurg_to_task() to also use
do_send_sig_info() which looses the check_kill_permission() check, but
your previous changes lost that same thing from SIGIO -- so I'm hoping
that's ok.

> Otherwise, personally I think this is what we need to solve the problem.

yay!

I'll look over the bits again and send out a -v4 later today.

----
Index: linux-2.6/fs/fcntl.c
===================================================================
--- linux-2.6.orig/fs/fcntl.c
+++ linux-2.6/fs/fcntl.c
@@ -287,6 +287,9 @@ static int f_setown_ex(struct file *filp
 	case F_OWNER_GID:
 		type = PIDTYPE_PGID;
 		break;
+
+	default:
+		return -EINVAL;
 	}
 
 	rcu_read_lock();
@@ -564,10 +567,10 @@ void send_sigio(struct fown_struct *fown
 }
 
 static void send_sigurg_to_task(struct task_struct *p,
-                                struct fown_struct *fown)
+                                struct fown_struct *fown, int group)
 {
 	if (sigio_perm(p, fown, SIGURG))
-		group_send_sig_info(SIGURG, SEND_SIG_PRIV, p);
+		do_send_sig_info(SIGURG, SEND_SIG_PRIV, p, group);
 }
 
 int send_sigurg(struct fown_struct *fown)
@@ -575,10 +578,17 @@ int send_sigurg(struct fown_struct *fown
 	struct task_struct *p;
 	enum pid_type type;
 	struct pid *pid;
+	int group = 1;
 	int ret = 0;
 	
 	read_lock(&fown->lock);
+
 	type = fown->pid_type;
+	if (type == PIDTYPE_MAX) {
+		group = 0;
+		type = PIDTYPE_PID;
+	}
+
 	pid = fown->pid;
 	if (!pid)
 		goto out_unlock_fown;
@@ -587,7 +597,7 @@ int send_sigurg(struct fown_struct *fown
 	
 	read_lock(&tasklist_lock);
 	do_each_pid_task(pid, type, p) {
-		send_sigurg_to_task(p, fown);
+		send_sigurg_to_task(p, fown, group);
 	} while_each_pid_task(pid, type, p);
 	read_unlock(&tasklist_lock);
  out_unlock_fown:



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