linux-kernel - Re: [PATCH] security: inode: fix a missing check for securityfs_create

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Date:   Wed, 10 Apr 2019 19:01:57 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     James Morris <jmorris@...ei.org>
Cc:     Kangjie Lu <kjlu@....edu>, pakki001@....edu,
        "Serge E. Hallyn" <serge@...lyn.com>,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] security: inode: fix a missing check for
 securityfs_create_file

On Thu, Apr 11, 2019 at 03:34:43AM +1000, James Morris wrote:
> On Fri, 15 Mar 2019, Kangjie Lu wrote:
> 
> > securityfs_create_file  may fail. The fix checks its status and
> > returns the error code upstream if it fails.
> > 
> > Signed-off-by: Kangjie Lu <kjlu@....edu>
> > 
> 
> Applied to
> git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security.git next-general
> 
> > ---
> > Return the exact error code upstream.
> > ---
> >  security/inode.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/security/inode.c b/security/inode.c
> > index b7772a9b315e..667f8b15027d 100644
> > --- a/security/inode.c
> > +++ b/security/inode.c
> > @@ -339,6 +339,11 @@ static int __init securityfs_init(void)
> >  #ifdef CONFIG_SECURITY
> >  	lsm_dentry = securityfs_create_file("lsm", 0444, NULL, NULL,
> >  						&lsm_ops);
> > +	if (IS_ERR(lsm_dentry)) {
> > +		unregister_filesystem(&fs_type);
> > +		sysfs_remove_mount_point(kernel_kobj, "security");
> > +		return PTR_ERR(lsm_dentry);
> > +	}

Rather bad way to do it - generally, register_filesystem() should be
the last thing done by initialization.  Any modular code that
does unregister_filesystem() on failure exit is flat-out broken;
here it's not instantly FUBAR, but it's a bloody bad example.

What's more, why not let simple_fill_super() do it?  Just
static int fill_super(struct super_block *sb, void *data, int silent)
{
        static const struct tree_descr files[] = {
#ifdef CONFIG_SECURITY
		{"lsm", &lsm_ops, 0444},
#endif
		{""}
	};

and to hell with that call of securityfs_create_file() and all its
failure handling...