linux-kernel - Re: [PATCH v2] tty: rocket: Fix a kernel address leak in rp

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Date:   Sun, 31 Mar 2019 13:37:56 +0530
From:   Mukesh Ojha <mojha@...eaurora.org>
To:     Fuqian Huang <huangfq.daxian@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] tty: rocket: Fix a kernel address leak in rp_ioctl


On 3/31/2019 11:02 AM, Fuqian Huang wrote:
> If the cmd is RCPK_GET_STRUCT, copy_to_user will copy
> info to user space. As info->port.ops is the address of
> a constant object rocket_port_ops (assigned in init_r_port),
> a kernel address leakage happens.
>
> This patch sets all the pointer fields to NULL before copy the
> object to user space to avoid kernel address leakage.


Should not this be done like provide userspace the stuff they want?

>
> Signed-off-by: Fuqian Huang <huangfq.daxian@...il.com>
> ---
>   drivers/tty/rocket.c | 31 +++++++++++++++++++++++++++++--
>   1 file changed, 29 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/tty/rocket.c b/drivers/tty/rocket.c
> index b121d8f8f3d7..a7bcf44b61bd 100644
> --- a/drivers/tty/rocket.c
> +++ b/drivers/tty/rocket.c
> @@ -1271,6 +1271,34 @@ static int get_version(struct r_port *info, struct rocket_version __user *retver
>   	return 0;
>   }
>   
> +static int get_struct(struct r_port *info, void *argp)
Should not this void * argp be struct r_port __user ?
> +{
> +	struct r_port *new;
> +	int ret = 0;
> +
> +	new = kzalloc(sizeof (struct r_port), GFP_KERNEL)

why there is space before sizeof everywhere ?

> ;
> +	if (!new)
> +		return -ENOMEM;
> +	memcpy(new, info, sizeof (struct r_port));
> +	new->port.tty = NULL;
> +	new->port.itty = NULL;
> +	new->port.ops = NULL;
> +	new->port.client_ops = NULL;
> +	memset(&new->port.open_wait.head, 0, sizeof (struct list_head));
> +	memset(&new->port.delta_msr_wait.head, 0, sizeof (struct list_head));
> +	memset(&new->port.mutex.wait_list, 0, sizeof (struct list_head));
> +	memset(&new->port.buf_mutex.wait_list, 0, sizeof (struct list_head));
> +	new->port.xmit_buf = NULL;
> +	new->port.client_data = NULL;
> +	new->ctlp = NULL;
> +	new->xmit_buf = NULL;
> +	memset(&new->write_mtx.wait_list, 0, sizeof (struct list_head));

Are we sure nothing is missed ?

Are the other information use by userspace ?


> +	if (copy_to_user(argp, new, sizeof (struct r_port)))
> +		ret = -EFAULT;
> +	kfree(new);
> +	return ret;
> +}
> +
>   /*  IOCTL call handler into the driver */
>   static int rp_ioctl(struct tty_struct *tty,
>   		    unsigned int cmd, unsigned long arg)
> @@ -1284,8 +1312,7 @@ static int rp_ioctl(struct tty_struct *tty,
>   
>   	switch (cmd) {
>   	case RCKP_GET_STRUCT:
> -		if (copy_to_user(argp, info, sizeof (struct r_port)))
> -			ret = -EFAULT;
> +		ret = get_struct(info, argp);
>   		break;
>   	case RCKP_GET_CONFIG:
>   		ret = get_config(info, argp);