[PATCH] usb: gadget: fix null pointer dereference in usb_put_function_instance()

[Jeffin Philip]

usb_put_function_instance() attempts to dereference fd inside fi struct
to get mod in uvc_alloc_inst() error path. However, fd is not allocated
until later in try_get_usb_function_instance() after allocating fi in
uvc_alloc_inst() and thus guranteed to be null in error path. Fix this
by adding a null check for fi->fd that returns if fd is null.

Reported-by: syzbot+fd6ef980cf1c722be639@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=fd6ef980cf1c722be639
Fixes: 0062f6e56f70 ("usb: gadget: add a forward pointer from usb_function to its "instance"")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Jeffin Philip <jeffinphilip14@xxxxxxxxx>
---
 drivers/usb/gadget/functions.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/functions.c b/drivers/usb/gadget/functions.c
index 203361a64212..70e31c40e267 100644
--- a/drivers/usb/gadget/functions.c
+++ b/drivers/usb/gadget/functions.c
@@ -70,7 +70,7 @@ void usb_put_function_instance(struct usb_function_instance *fi)
 {
 	struct module *mod;
 
-	if (!fi)
+	if (!fi || !fi->fd)
 		return;
 
 	mod = fi->fd->mod;
-- 
2.55.0