[PATCH] lguest: make sure cpu is initialized before accessing it

[PATCH] lguest: make sure cpu is initialized before accessing it

[Eugene Teo]

If req is LHREQ_INITIALIZE, and the guest has been initialized before
(unlikely), it will attempt to access cpu->tsk even though cpu is not yet
initialized.

Signed-off-by: Eugene Teo <eugeneteo@kernel.sg>
---
 drivers/lguest/lguest_user.c |   14 +++++++-------
 1 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/lguest/lguest_user.c b/drivers/lguest/lguest_user.c
index 85d42d3..9cbb285 100644
--- a/drivers/lguest/lguest_user.c
+++ b/drivers/lguest/lguest_user.c
@@ -241,15 +241,15 @@ static ssize_t write(struct file *file, const char __user *in,
 		cpu = &lg->cpus[cpu_id];
 		if (!cpu)
 			return -EINVAL;
-	}
 
-	/* Once the Guest is dead, all you can do is read() why it died. */
-	if (lg && lg->dead)
-		return -ENOENT;
+		/* Once the Guest is dead, all you can do is read() why it died. */
+		if (lg && lg->dead)
+			return -ENOENT;
 
-	/* If you're not the task which owns the Guest, you can only break */
-	if (lg && current != cpu->tsk && req != LHREQ_BREAK)
-		return -EPERM;
+		/* If you're not the task which owns the Guest, you can only break */
+		if (lg && current != cpu->tsk && req != LHREQ_BREAK)
+			return -EPERM;
+	}
 
 	switch (req) {
 	case LHREQ_INITIALIZE:

Re: [PATCH] lguest: make sure cpu is initialized before accessing it

[Rusty Russell]

On Tuesday 04 March 2008 10:15:47 Rusty Russell wrote:
> On Sunday 10 February 2008 02:53:17 Eugene Teo wrote:
> > If req is LHREQ_INITIALIZE, and the guest has been initialized before
> > (unlikely), it will attempt to access cpu->tsk even though cpu is not yet
> > initialized.
> >
> > Signed-off-by: Eugene Teo <eugeneteo@kernel.sg>

Thanks Eugene, I've applied this with some wrapping of the comments and 
removal of the now-redundant lg != NULL tests:

> > +		/* Once the Guest is dead, all you can do is read() why it died. */
> > +		if (lg && lg->dead)
> > +			return -ENOENT;
> >
> > -	/* If you're not the task which owns the Guest, you can only break */
> > -	if (lg && current != cpu->tsk && req != LHREQ_BREAK)
> > -		return -EPERM;
> > +		/* If you're not the task which owns the Guest, you can only break */
> > +		if (lg && current != cpu->tsk && req != LHREQ_BREAK)
> > +			return -EPERM;
> > +	}

Cheers,
Rusty.