[PATCH 4.9 36/46] uio: Fix an Oops on load

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Carpenter <dan.carpenter@oracle.com>

commit 432798195bbce1f8cd33d1c0284d0538835e25fb upstream.

I was trying to solve a double free but I introduced a more serious
NULL dereference bug.  The problem is that if there is an IRQ which
triggers immediately, then we need "info->uio_dev" but it's not set yet.

This patch puts the original initialization back to how it was and just
sets info->uio_dev to NULL on the error path so it should solve both
the Oops and the double free.

Fixes: f019f07ecf6a ("uio: potential double frees if __uio_register_device() fails")
Reported-by: Mathias Thore <Mathias.Thore@infinera.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: stable <stable@vger.kernel.org>
Tested-by: Mathias Thore <Mathias.Thore@infinera.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/uio/uio.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/drivers/uio/uio.c
+++ b/drivers/uio/uio.c
@@ -850,6 +850,8 @@ int __uio_register_device(struct module
 	if (ret)
 		goto err_uio_dev_add_attributes;
 
+	info->uio_dev = idev;
+
 	if (info->irq && (info->irq != UIO_IRQ_CUSTOM)) {
 		/*
 		 * Note that we deliberately don't use devm_request_irq
@@ -861,11 +863,12 @@ int __uio_register_device(struct module
 		 */
 		ret = request_irq(info->irq, uio_interrupt,
 				  info->irq_flags, info->name, idev);
-		if (ret)
+		if (ret) {
+			info->uio_dev = NULL;
 			goto err_request_irq;
+		}
 	}
 
-	info->uio_dev = idev;
 	return 0;
 
 err_request_irq: