linux-kernel - Re: [PATCH] staging: pi433: add mutex fixing race condition when accessing tx

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Message-ID: <20180612110230.dvqmcyisdwaynixj@mwanda>
Date:   Tue, 12 Jun 2018 14:02:30 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Hugo Lefeuvre <hle@....eu.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        kernelnewbies@...nelnewbies.org
Subject: Re: [PATCH] staging: pi433: add mutex fixing race condition when
 accessing tx_cfg

On Mon, Jun 11, 2018 at 09:12:00PM -0400, Hugo Lefeuvre wrote:
> In the PI433_IOC_WR_TX_CFG case in pi433_ioctl, instance->tx_cfg is
> modified using
> 
> copy_from_user(&instance->tx_cfg, argp, sizeof(struct pi433_tx_cfg)))
> 
> without any kind of synchronization. In the case where two threads
> would execute this same command concurrently the tx_cfg field might
> enter in an inconsistent state.
> 
> Add a mutex making sure that the PI433_IOC_WR_TX_CFG case will never
> be run by several threads concurrently.
> 
> Signed-off-by: Hugo Lefeuvre <hle@....eu.com>

We read the data from the user here and then we write it to the fifo
in pi433_write().  We should be using the device->tx_fifo_lock so that
we don't copy over the data at the same time we're writing it to the
fifo.

This bug could cause a user space program to fail.

regards,
dan carpenter