[PATCH] usb: gadget: acm: set notify_req to NULL after freed to avoid double free

[changbin.du@intel.com]

From: "Du, Changbin" <changbin.du@intel.com>

If acm_bind fails before allocate notification and acm->notify_req is
not set to NULL after freed last time, double free will happen.

kernel BUG at mm/slub.c:3392!
invalid opcode: 0000 [#1] PREEMPT SMP
EIP is at kfree+0x172/0x180
Call Trace:
[<80c0e3b6>] ? usb_ep_autoconfig_ss+0x86/0x170
[<80c13345>] gs_free_req+0x15/0x30
[<80c12df1>] acm_bind+0x1c1/0x2d0
[<80c0e9be>] usb_add_function+0x6e/0x120
[<80c213cb>] acm_function_bind_config+0x2b/0x90

Signed-off-by: Du, Changbin <changbin.du@intel.com>
---
 drivers/usb/gadget/function/f_acm.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/function/f_acm.c b/drivers/usb/gadget/function/f_acm.c
index 2fa1e80..e10c8d4 100644
--- a/drivers/usb/gadget/function/f_acm.c
+++ b/drivers/usb/gadget/function/f_acm.c
@@ -699,8 +699,10 @@ acm_bind(struct usb_configuration *c, struct usb_function *f)
 	return 0;
 
 fail:
-	if (acm->notify_req)
+	if (acm->notify_req) {
 		gs_free_req(acm->notify, acm->notify_req);
+		acm->notify_req = NULL;
+	}
 
 	ERROR(cdev, "%s/%p: can't bind, err %d\n", f->name, f, status);
 
@@ -713,8 +715,10 @@ static void acm_unbind(struct usb_configuration *c, struct usb_function *f)
 
 	acm_string_defs[0].id = 0;
 	usb_free_all_descriptors(f);
-	if (acm->notify_req)
+	if (acm->notify_req) {
 		gs_free_req(acm->notify, acm->notify_req);
+		acm->notify_req = NULL;
+	}
 }
 
 static void acm_free_func(struct usb_function *f)
-- 
2.5.0