2017-03-28 12:10:48

by Ajay Kaher

Subject: [PATCH v4] USB: Proper handling of Race Condition when two USB class drivers try to call init_usb_class simultaneously

Greg, sending patch again using git send-email, please apply.
Let me know if still any issue.

There is race condition when two USB class drivers try to call
init_usb_class at the same time and leads to crash.
code path: probe->usb_register_dev->init_usb_class

To solve this, mutex locking has been added in init_usb_class() and
destroy_usb_class().

As pointed by Alan, removed "if (usb_class)" test from destroy_usb_class()
because usb_class can never be NULL there.

Signed-off-by: Ajay Kaher <[email protected]>
Acked-by: Alan Stern <[email protected]>
---
drivers/usb/core/file.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/core/file.c b/drivers/usb/core/file.c
index 822ced9..422ce7b 100644
--- a/drivers/usb/core/file.c
+++ b/drivers/usb/core/file.c
@@ -27,6 +27,7 @@
#define MAX_USB_MINORS 256
static const struct file_operations *usb_minors[MAX_USB_MINORS];
static DECLARE_RWSEM(minor_rwsem);
+static DEFINE_MUTEX(init_usb_class_mutex);

static int usb_open(struct inode *inode, struct file *file)
{
@@ -109,8 +110,9 @@ static void release_usb_class(struct kref *kref)

static void destroy_usb_class(void)
{
- if (usb_class)
- kref_put(&usb_class->kref, release_usb_class);
+ mutex_lock(&init_usb_class_mutex);
+ kref_put(&usb_class->kref, release_usb_class);
+ mutex_unlock(&init_usb_class_mutex);
}

int usb_major_init(void)
@@ -171,7 +173,10 @@ int usb_register_dev(struct usb_interface *intf,
if (intf->minor >= 0)
return -EADDRINUSE;

+ mutex_lock(&init_usb_class_mutex);
retval = init_usb_class();
+ mutex_unlock(&init_usb_class_mutex);
+
if (retval)
return retval;

--
2.7.4

2017-03-29 09:56:53

by Greg Kroah-Hartman

Subject: Re: [PATCH v4] USB: Proper handling of Race Condition when two USB class drivers try to call init_usb_class simultaneously

On Tue, Mar 28, 2017 at 08:09:32AM -0400, Ajay Kaher wrote:
> Greg, sending patch again using git send-email, please apply.
> Let me know if still any issue.

Note, please put comments like this below the --- line so I don't have
to manually edit the file by hand.

I've now queued this up, thanks.

greg k-h