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

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Message-ID: <20200802165535.GA270694@PWN>
Date:   Sun, 2 Aug 2020 12:55:35 -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:
> kernel/signal.c:3524 __do_sys_rt_sigtimedwait() warn: check that 'info' doesn't leak information (struct has a hole after 'si_code')
> kernel/signal.c:3524 __do_sys_rt_sigtimedwait() warn: check that 'info' doesn't leak information (struct has a hole after 'si_code')
> kernel/signal.c:3556 __do_sys_rt_sigtimedwait_time32() warn: check that 'info' doesn't leak information (struct has a hole after 'si_code')
> kernel/signal.c:3556 __do_sys_rt_sigtimedwait_time32() warn: check that 'info' doesn't leak information (struct has a hole after 'si_code')

I think these are safe. Before getting to copy_siginfo_to_user(), all
`info` run through:

	do_sigtimedwait()
		V
	dequeue_signal()
		V
       __dequeue_signal()
		V
	collect_signal()

Where it either gets memcpy()'d by copy_siginfo(), or memset()'d by
clear_siginfo().

The only exception is when next_signal() fails in __dequeue_signal(),
but that will cause do_sigtimedwait() to return an error, and we never
reach copy_siginfo_to_user() in such a case.

Thank you,
Peilin Ye