[34-longterm 102/209] HID: hidraw, fix a NULL pointer dereference in hidraw_ioctl

[Paul Gortmaker]

From: Antonio Ospite <ospite@xxxxxxxxxxxxxxxxx>

  =====================================================================
  | This is a commit scheduled for the next v2.6.34 longterm release. |
  | If you see a problem with using this for longterm, please comment.|
  =====================================================================

commit d20d5ffab92f00188f360c44c791a5ffb988247c upstream.

BUG: unable to handle kernel NULL pointer dereference at 0000000000000028
IP: [<ffffffffa02c66b4>] hidraw_ioctl+0xfc/0x32c [hid]
[...]

This is reproducible by disconnecting the device while userspace does
ioctl in a loop and doesn't check return values in order to exit the
loop.

[PG: slightly/trivially reworked for backport to 34]

Signed-off-by: Antonio Ospite <ospite@xxxxxxxxxxxxxxxxx>
Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
---
 drivers/hid/hidraw.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/drivers/hid/hidraw.c b/drivers/hid/hidraw.c
index 6eadf1a..0db1a0f 100644
--- a/drivers/hid/hidraw.c
+++ b/drivers/hid/hidraw.c
@@ -243,6 +243,11 @@ static long hidraw_ioctl(struct file *file, unsigned int cmd,
 	void __user *user_arg = (void __user*) arg;
 
 	lock_kernel();
+	if (!dev) {
+		ret = -ENODEV;
+		goto out;
+	}
+
 	switch (cmd) {
 		case HIDIOCGRDESCSIZE:
 			if (put_user(dev->hid->rsize, (int __user *)arg))
@@ -315,6 +320,7 @@ static long hidraw_ioctl(struct file *file, unsigned int cmd,
 
 		ret = -ENOTTY;
 	}
+out:
 	unlock_kernel();
 	return ret;
 }
-- 
1.7.4.4

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