[Linux-kernel-mentees] [PATCH] Media: Radio: Change devm_k*alloc to k*alloc

[lnowakow at eng.ucsd.edu (Luke Nowakowski-Krijger)]

This patch aims to fix the use-after-free read described in
https://syzkaller.appspot.com/bug?extid=a4387f5b6b799f6becbf

Changes devm_k*alloc to k*alloc which manually frees memory allocated by
raremono_device instead of leaving it to be automatically deallocated
when the USB interface calls it to be freed. The devices resources are
freed in usb_raremono_disconnect as well as freed when error conditions
occur in usb_raremono_probe.

This change is necessary due to the fact that when the USB device is
disconnected, it frees the raremono_device structure before doing the
necessary cleanup to remove references to the device, thus we get these
use-after-free errors.

I would like to thank Hans Verkuil for pointing me in the right
direction to fix this issue.

Signed-off-by: Luke Nowakowski-Krijger <lnowakow at eng.ucsd.edu>

---
 ?drivers/media/radio/radio-raremono.c | 18 +++++++++++++-----
 ?1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/drivers/media/radio/radio-raremono.c b/drivers/media/radio/radio-raremono.c
index 5e782b3c2fa9..88cff46cde28 100644
--- a/drivers/media/radio/radio-raremono.c
+++ b/drivers/media/radio/radio-raremono.c
@@ -171,6 +171,8 @@ static void usb_raremono_disconnect(struct usb_interface *intf)
 ??????? v4l2_device_disconnect(&radio->v4l2_dev);
 ??????? mutex_unlock(&radio->lock);
 ??????? v4l2_device_put(&radio->v4l2_dev);
+?????? kfree(radio->buffer);
+?????? kfree(radio);
 ?}

 ?/*
@@ -295,12 +297,15 @@ static int usb_raremono_probe(struct usb_interface *intf,
 ??????? struct raremono_device *radio;
 ??????? int retval = 0;

-?????? radio = devm_kzalloc(&intf->dev, sizeof(struct raremono_device), GFP_KERNEL);
-?????? if (radio)
-?????????????? radio->buffer = devm_kmalloc(&intf->dev, BUFFER_LENGTH, GFP_KERNEL);
-
-?????? if (!radio || !radio->buffer)
+?????? radio = kzalloc(sizeof(struct raremono_device), GFP_KERNEL);
+?????? if (!radio)
+?????????????? return -ENOMEM;
+
+?????? radio->buffer = kmalloc(BUFFER_LENGTH, GFP_KERNEL);
+?????? if (!radio->buffer) {
+?????????????? kfree(radio);
 ??????????????? return -ENOMEM;
+?????? }

 ??????? radio->usbdev = interface_to_usbdev(intf);
 ??????? radio->intf = intf;
@@ -324,6 +329,9 @@ static int usb_raremono_probe(struct usb_interface *intf,
 ??????? if (retval != 3 ||
 ??????????? (get_unaligned_be16(&radio->buffer[1]) & 0xfff) == 0x0242) {
 ??????????????? dev_info(&intf->dev, "this is not Thanko's Raremono.\n");
+
+?????????????? kfree(radio->buffer);
+?????????????? kfree(radio);
 ??????????????? return -ENODEV;
 ??????? }

-- 
2.20.1