ACK: [CVE-2016-10088][PATCH Trusty] sg_write()/bsg_write() is not fit to be called under KERNEL_DS

[Stefan Bader]

On 20.06.2017 10:58, Po-Hsu Lin wrote:
> From: Al Viro <viro at zeniv.linux.org.uk>
> 
> CVE-2016-10088
> 
> Both damn things interpret userland pointers embedded into the payload;
> worse, they are actually traversing those.  Leaving aside the bad
> API design, this is very much _not_ safe to call with KERNEL_DS.
> Bail out early if that happens.
> 
> Cc: stable at vger.kernel.org
> Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
> (cherry picked from commit 128394eff343fc6d2f32172f03e24829539c5835)
> 
> Signed-off-by: Po-Hsu Lin <po-hsu.lin at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>

> ---
>  block/bsg.c       |    3 +++
>  drivers/scsi/sg.c |    3 +++
>  2 files changed, 6 insertions(+)
> 
> diff --git a/block/bsg.c b/block/bsg.c
> index 420a5a9..76801e5 100644
> --- a/block/bsg.c
> +++ b/block/bsg.c
> @@ -675,6 +675,9 @@ bsg_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
>  
>  	dprintk("%s: write %Zd bytes\n", bd->name, count);
>  
> +	if (unlikely(segment_eq(get_fs(), KERNEL_DS)))
> +		return -EINVAL;
> +
>  	bsg_set_block(bd, file);
>  
>  	bytes_written = 0;
> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
> index 1f65e32..291791a 100644
> --- a/drivers/scsi/sg.c
> +++ b/drivers/scsi/sg.c
> @@ -568,6 +568,9 @@ sg_write(struct file *filp, const char __user *buf, size_t count, loff_t * ppos)
>  	sg_io_hdr_t *hp;
>  	unsigned char cmnd[MAX_COMMAND_SIZE];
>  
> +	if (unlikely(segment_eq(get_fs(), KERNEL_DS)))
> +		return -EINVAL;
> +
>  	if ((!(sfp = (Sg_fd *) filp->private_data)) || (!(sdp = sfp->parentdp)))
>  		return -ENXIO;
>  	SCSI_LOG_TIMEOUT(3, printk("sg_write: %s, count=%d\n",
> 


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