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Date:   Wed, 5 Jun 2019 08:41:11 +0200
From:   Jiri Slaby <>
To:     Gen Zhang <>,,,
Subject: Re: [PATCH] sg: fix a double-fetch bug in sg_write()

On 31. 05. 19, 3:27, Gen Zhang wrote:
> In sg_write(), the opcode of the command is fetched the first time from 
> the userspace by __get_user(). Then the whole command, the opcode 
> included, is fetched again from userspace by __copy_from_user(). 
> However, a malicious user can change the opcode between the two fetches.
> This can cause inconsistent data and potential errors as cmnd is used in
> the following codes.
> Thus we should check opcode between the two fetches to prevent this.
> Signed-off-by: Gen Zhang <>
> ---
> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
> index d3f1531..a2971b8 100644
> --- a/drivers/scsi/sg.c
> +++ b/drivers/scsi/sg.c
> @@ -694,6 +694,8 @@ sg_write(struct file *filp, const char __user *buf, size_t count, loff_t * ppos)
>  	hp->flags = input_size;	/* structure abuse ... */
>  	hp->pack_id = old_hdr.pack_id;
>  	hp->usr_ptr = NULL;
> +	if (opcode != cmnd[0])
> +		return -EINVAL;
>  	if (__copy_from_user(cmnd, buf, cmd_size))
>  		return -EFAULT;

You are sending the same patches like a broken machine. Please STOP this
and give people some time to actually review your patches! (Don't expect
replies in days.)

I already commented on this apparently broken one earlier...

suse labs

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