[PATCH 8/9] USB usbfs: missing lock in proc_getdriver

[PATCH 8/9] USB usbfs: missing lock in proc_getdriver

[Duncan Sands]

Protect against driver binding changes while reading the driver name.

 devio.c |   14 ++++++++------
 1 files changed, 8 insertions(+), 6 deletions(-)


diff -Nru a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
--- a/drivers/usb/core/devio.c	Wed Apr 14 12:18:30 2004
+++ b/drivers/usb/core/devio.c	Wed Apr 14 12:18:30 2004
@@ -709,12 +709,14 @@
 	if ((ret = findintfif(ps->dev, gd.interface)) < 0)
 		return ret;
 	interface = ps->dev->actconfig->interface[ret];
-	if (!interface->dev.driver)
-		return -ENODATA;
-	strncpy(gd.driver, interface->dev.driver->name, sizeof(gd.driver));
-	if (copy_to_user(arg, &gd, sizeof(gd)))
-		return -EFAULT;
-	return 0;
+	ret = -ENODATA;
+	down_read(&usb_bus_type.subsys.rwsem);
+	if (interface && interface->dev.driver) {
+		strncpy(gd.driver, interface->dev.driver->name, sizeof(gd.driver));
+		ret = copy_to_user(arg, &gd, sizeof(gd)) ? -EFAULT : 0;
+	}
+	up_read(&usb_bus_type.subsys.rwsem);
+	return ret;
 }
 
 static int proc_connectinfo(struct dev_state *ps, void __user *arg)

Re: [linux-usb-devel] [PATCH 8/9] USB usbfs: missing lock in proc_getdriver

[Oliver Neukum]

> +	down_read(&usb_bus_type.subsys.rwsem);
> +	if (interface && interface->dev.driver) {
> +		strncpy(gd.driver, interface->dev.driver->name, sizeof(gd.driver));
> +		ret = copy_to_user(arg, &gd, sizeof(gd)) ? -EFAULT : 0;
> +	}
> +	up_read(&usb_bus_type.subsys.rwsem);
> +	return ret;

IMHO you should drop the lock before you copy to userspace.

	Regards
		Oliver

Re: [linux-usb-devel] [PATCH 8/9] USB usbfs: missing lock in proc_getdriver

[Duncan Sands]

On Wednesday 14 April 2004 13:04, Oliver Neukum wrote:
> > +	down_read(&usb_bus_type.subsys.rwsem);
> > +	if (interface && interface->dev.driver) {
> > +		strncpy(gd.driver, interface->dev.driver->name, sizeof(gd.driver));
> > +		ret = copy_to_user(arg, &gd, sizeof(gd)) ? -EFAULT : 0;
> > +	}
> > +	up_read(&usb_bus_type.subsys.rwsem);
> > +	return ret;
>
> IMHO you should drop the lock before you copy to userspace.

Hi Oliver, I wasn't particularly worried about it since it's a rwsem taken for
reading and writing is a rare event.  Do you think it really matters?  If so,
how about this instead (compiles but otherwise untested):

@@ -702,13 +708,15 @@
 		return -EFAULT;
 	if ((ret = findintfif(ps->dev, gd.interface)) < 0)
 		return ret;
+	down_read(&usb_bus_type.subsys.rwsem);
 	interface = ps->dev->actconfig->interface[ret];
-	if (!interface->dev.driver)
+	if (!interface || !interface->dev.driver) {
+		up_read(&usb_bus_type.subsys.rwsem);
 		return -ENODATA;
+	}
 	strncpy(gd.driver, interface->dev.driver->name, sizeof(gd.driver));
-	if (copy_to_user(arg, &gd, sizeof(gd)))
-		return -EFAULT;
-	return 0;
+	up_read(&usb_bus_type.subsys.rwsem);
+	return copy_to_user(arg, &gd, sizeof(gd)) ? -EFAULT : 0;
 }
 
 static int proc_connectinfo(struct dev_state *ps, void __user *arg)

Re: [linux-usb-devel] [PATCH 8/9] USB usbfs: missing lock in proc_getdriver

[Oliver Neukum]

Am Mittwoch, 14. April 2004 13:37 schrieb Duncan Sands:
> On Wednesday 14 April 2004 13:04, Oliver Neukum wrote:
> > > +	down_read(&usb_bus_type.subsys.rwsem);
> > > +	if (interface && interface->dev.driver) {
> > > +		strncpy(gd.driver, interface->dev.driver->name, sizeof(gd.driver));
> > > +		ret = copy_to_user(arg, &gd, sizeof(gd)) ? -EFAULT : 0;
> > > +	}
> > > +	up_read(&usb_bus_type.subsys.rwsem);
> > > +	return ret;
> >
> > IMHO you should drop the lock before you copy to userspace.
>
> Hi Oliver, I wasn't particularly worried about it since it's a rwsem taken
> for reading and writing is a rare event.  Do you think it really matters? 
> If so, how about this instead (compiles but otherwise untested):

Hi,

I expect it to rarely matter, but it might matter now and then. It's
just a question of hygiene. If you are using a temporary buffer I'd
like to see it used to full advantage. So either drop the lock or do
a direct copy. I'd prefer the first option your patch implemented.

	Regards
		Oliver

Re: [linux-usb-devel] [PATCH 8/9] USB usbfs: missing lock in proc_getdriver

[Duncan Sands]

Hi Oliver,

> I expect it to rarely matter, but it might matter now and then. It's
> just a question of hygiene. If you are using a temporary buffer I'd
> like to see it used to full advantage. So either drop the lock or do
> a direct copy. I'd prefer the first option your patch implemented.

I agree.  Greg, please consider applying the updated patch:

--- gregkh-2.6/drivers/usb/core/devio.c.orig	2004-04-14 16:02:44.000000000 +0200
+++ gregkh-2.6/drivers/usb/core/devio.c	2004-04-14 16:03:12.000000000 +0200
@@ -702,13 +708,15 @@
 		return -EFAULT;
 	if ((ret = findintfif(ps->dev, gd.interface)) < 0)
 		return ret;
+	down_read(&usb_bus_type.subsys.rwsem);
 	interface = ps->dev->actconfig->interface[ret];
-	if (!interface->dev.driver)
+	if (!interface || !interface->dev.driver) {
+		up_read(&usb_bus_type.subsys.rwsem);
 		return -ENODATA;
+	}
 	strncpy(gd.driver, interface->dev.driver->name, sizeof(gd.driver));
-	if (copy_to_user(arg, &gd, sizeof(gd)))
-		return -EFAULT;
-	return 0;
+	up_read(&usb_bus_type.subsys.rwsem);
+	return copy_to_user(arg, &gd, sizeof(gd)) ? -EFAULT : 0;
 }
 
 static int proc_connectinfo(struct dev_state *ps, void __user *arg)