linux-kernel - Re: [PATCH RFC 4/5] UBIFS: Add security.* XATTR support for the UBIFS

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Date:	Fri, 22 Feb 2013 09:10:37 +0200
From:	Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>
To:	Marc Kleine-Budde <mkl@...gutronix.de>
Cc:	linux-mtd@...ts.infradead.org, kernel@...gutronix.de,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	Subodh Nijsure <snijsure@...d-net.com>
Subject: Re: [PATCH RFC 4/5] UBIFS: Add security.* XATTR support for the
 UBIFS

OK, the lockdep warnings clearly tell the reason:

        CPU0                    CPU1
        ----                    ----
   lock(&ui->ui_mutex);
                                lock(&sb->s_type->i_mutex_key#10);
                                lock(&ui->ui_mutex);
   lock(&sb->s_type->i_mutex_key#10);

And then there are 2 tracebacks which are useful and show that you
unnecessarily initialize the inode security contenxt whil holding the
parent inode lock. I think you do not need to hold that lock. Move the
initialization out of the protected section.

See below my suggestions.

On Wed, 2013-02-13 at 11:23 +0100, Marc Kleine-Budde wrote:
> @@ -280,6 +280,10 @@ static int ubifs_create(struct inode *dir, struct dentry *dentry, umode_t mode,
>  	err = ubifs_jnl_update(c, dir, &dentry->d_name, inode, 0, 0);
>  	if (err)
>  		goto out_cancel;
> +
> +	err = ubifs_init_security(dir, inode, &dentry->d_name);
> +	if (err)
> +		goto out_cancel;
>  	mutex_unlock(&dir_ui->ui_mutex);

Can you move ubifs_init_security() up to before
'mutex_lock(&dir_ui->ui_mutex)'

> @@ -742,6 +746,10 @@ static int ubifs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
...
> +	err = ubifs_init_security(dir, inode, &dentry->d_name);
> +	if (err)
> +		goto out_cancel;
>  	mutex_unlock(&dir_ui->ui_mutex);

Ditto.

> @@ -818,6 +826,10 @@ static int ubifs_mknod(struct inode *dir, struct dentry *dentry,
...
> +	err = ubifs_init_security(dir, inode, &dentry->d_name);
> +	if (err)
> +		goto out_cancel;
>  	mutex_unlock(&dir_ui->ui_mutex);

Ditto.

> @@ -894,6 +906,10 @@ static int ubifs_symlink(struct inode *dir, struct dentry *dentry,
...
> +	err = ubifs_init_security(dir, inode, &dentry->d_name);
> +	if (err)
> +		goto out_cancel;
>  	mutex_unlock(&dir_ui->ui_mutex);

Ditto.

> +int ubifs_init_security(struct inode *dentry, struct inode *inode,
> +			const struct qstr *qstr)
> +{
> +	int err;
> +
> +	mutex_lock(&inode->i_mutex);
> +	err = security_inode_init_security(inode, dentry, qstr,
> +					   &ubifs_initxattrs, 0);
> +	mutex_unlock(&inode->i_mutex);

I did not verify, but I doubt that you need i_mutex here, because you
only call this function when you create an inode, before it becomes
visible to VFS. Please, double-check this.

Thanks!

-- 
Best Regards,
Artem Bityutskiy

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