linux-kernel - Re: [Linux-kernel-mentees] [PATCH v3] media/v4l2-core: Fix kernel-infoleak in video_put

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Date:   Mon, 27 Jul 2020 18:33:57 -0400
From:   Peilin Ye <yepeilin.cs@...il.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Linux-kernel-mentees] [PATCH v3] media/v4l2-core: Fix
 kernel-infoleak in video_put_user()

On Mon, Jul 27, 2020 at 04:16:08PM +0300, Dan Carpenter wrote:
> drivers/block/floppy.c:3132 raw_cmd_copyout() warn: check that 'cmd' doesn't leak information (struct has a hole after 'flags')

(Removed some Cc: recipients from the list.)

I'm not very sure, but I think this one is also a false positive.

Here Smatch is complaining about a linked list called `my_raw_cmd`
defined in raw_cmd_ioctl():

drivers/block/floppy.c:3249:

	ret = raw_cmd_copyin(cmd, param, &my_raw_cmd);

In raw_cmd_copyin(), each element of the linked list is allocated by
kmalloc() then copied from user:

drivers/block/floppy.c:3180:

loop:
	ptr = kmalloc(sizeof(struct floppy_raw_cmd), GFP_KERNEL);
	      ^^^^^^^
	if (!ptr)
		return -ENOMEM;
	*rcmd = ptr;
	ret = copy_from_user(ptr, param, sizeof(*ptr));
	      ^^^^^^^^^^^^^^

I think copy_from_user() is filling in the paddings inside `struct
floppy_raw_cmd`?

Thank you,
Peilin Ye