linux-kernel - [PATCH] media: v4l2-core: only zero-out ioctl-read buffers

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Date:   Wed,  8 Jan 2020 11:00:00 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Arnd Bergmann <arnd@...db.de>
Cc:     syzbot+54fd8cca4b7226c94b8e@...kaller.appspotmail.com,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Vandana BN <bnvandana@...il.com>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] media: v4l2-core: only zero-out ioctl-read buffers

The memset() got moved out of the check for _IOC_NONE, so passing a
made-up command number with a size but no direction would allow clearing
data on user-provided pointers.

Move video_get_user() back into the _IOC_NONE check where it belongs.

Reported-by: syzbot+54fd8cca4b7226c94b8e@...kaller.appspotmail.com
Fixes: 6c625c01c7a6 ("media: v4l2-core: split out data copy from video_usercopy")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/media/v4l2-core/v4l2-ioctl.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
index b0d670715c27..0f11fc6b5447 100644
--- a/drivers/media/v4l2-core/v4l2-ioctl.c
+++ b/drivers/media/v4l2-core/v4l2-ioctl.c
@@ -3208,12 +3208,12 @@ video_usercopy(struct file *file, unsigned int orig_cmd, unsigned long arg,
 			parg = mbuf;
 		}
 
+		err = video_get_user((void __user *)arg, parg, orig_cmd,
+				     &always_copy);
+		if (err)
+			goto out;
 	}
 
-	err = video_get_user((void __user *)arg, parg, orig_cmd, &always_copy);
-	if (err)
-		goto out;
-
 	err = check_array_args(cmd, parg, &array_size, &user_ptr, &kernel_ptr);
 	if (err < 0)
 		goto out;
-- 
2.20.0