[Linux-kernel-mentees] [PATCH] Media: Radio: Change devm_k*alloc to k*alloc
Luke Nowakowski-Krijger
lnowakow at eng.ucsd.edu
Thu May 23 07:56:19 UTC 2019
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
More information about the Linux-kernel-mentees
mailing list