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Date:   Sun, 28 Mar 2021 18:07:02 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Miklos Szeredi <mszeredi@redhat.com>
Cc:     linux-fsdevel@vger.kernel.org,
        "Darrick J . Wong" <djwong@kernel.org>,
        Amir Goldstein <amir73il@gmail.com>,
        David Sterba <dsterba@suse.cz>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Eric Biggers <ebiggers@kernel.org>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 01/18] vfs: add fileattr ops
Message-ID: <YGDFxh7+724niztd@zeniv-ca.linux.org.uk>
References: <20210325193755.294925-1-mszeredi@redhat.com>
 <20210325193755.294925-2-mszeredi@redhat.com>
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Sender: Al Viro <viro@ftp.linux.org.uk>
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On Thu, Mar 25, 2021 at 08:37:38PM +0100, Miklos Szeredi wrote:

> +int vfs_fileattr_get(struct dentry *dentry, struct fileattr *fa)
> +{
> +	struct inode *inode = d_inode(dentry);
> +
> +	if (d_is_special(dentry))
> +		return -ENOTTY;

FWIW - why?  For uses via ioctl() you simply won't get there with
device nodes et.al. - they have file_operations of their own.
If we add syscall(s) for getting/setting those, there's no reason
for e.g. a device node not to have those attributes...

> +static int ioctl_getflags(struct file *file, void __user *argp)

unsigned int __user *argp, surely?

> +{
> +	struct fileattr fa = { .flags_valid = true }; /* hint only */
> +	unsigned int flags;
> +	int err;
> +
> +	err = vfs_fileattr_get(file->f_path.dentry, &fa);
> +	if (!err) {
> +		flags = fa.flags;
> +		if (copy_to_user(argp, &flags, sizeof(flags)))
> +			err = -EFAULT;

... and put_user() here.

> +	}
> +	return err;
> +}
> +
> +static int ioctl_setflags(struct file *file, void __user *argp)
> +{
> +	struct fileattr fa;
> +	unsigned int flags;
> +	int err;
> +
> +	if (copy_from_user(&flags, argp, sizeof(flags)))
> +		return -EFAULT;
> +
> +	err = mnt_want_write_file(file);
> +	if (!err) {
> +		fileattr_fill_flags(&fa, flags);
> +		err = vfs_fileattr_set(file_mnt_user_ns(file), file_dentry(file), &fa);
> +		mnt_drop_write_file(file);
> +	}
> +	return err;
> +}

Similar here.