linux-kernel - Re: [PATCH 1/7] powerpc/spufs: simplify spufs core dumping

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Date:   Tue, 21 Apr 2020 19:49:41 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Christoph Hellwig <hch@....de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jeremy Kerr <jk@...abs.org>, Arnd Bergmann <arnd@...db.de>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/7] powerpc/spufs: simplify spufs core dumping

On Tue, Apr 21, 2020 at 05:41:58PM +0200, Christoph Hellwig wrote:

>  static ssize_t spufs_proxydma_info_read(struct file *file, char __user *buf,
>  				   size_t len, loff_t *pos)
>  {
>  	struct spu_context *ctx = file->private_data;
> +	struct spu_proxydma_info info;
>  	int ret;
>  
> +	if (len < sizeof(info))
> +		return -EINVAL;
> +	if (!access_ok(buf, len))
> +		return -EFAULT;
> +
>  	ret = spu_acquire_saved(ctx);
>  	if (ret)
>  		return ret;
>  	spin_lock(&ctx->csa.register_lock);
> -	ret = __spufs_proxydma_info_read(ctx, buf, len, pos);
> +	__spufs_proxydma_info_read(ctx, &info);
> +	ret = simple_read_from_buffer(buf, len, pos, &info, sizeof(info));

IDGI...  What's that access_ok() for?  If you are using simple_read_from_buffer(),
the damn thing goes through copy_to_user().  Why bother with separate access_ok()
here?