From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Dave Chinner <david@fromorbit.com>,
linux-fsdevel@vger.kernel.org,
James Morris <james.l.morris@oracle.com>,
Andrew Morton <akpm@linux-foundation.org>,
Stephen Smalley <sds@tycho.nsa.gov>,
"Theodore Ts'o" <tytso@mit.edu>,
Eric Paris <eparis@parisplace.org>,
stable <stable@vger.kernel.org>, Paul Moore <paul@paul-moore.com>,
LKML <linux-kernel@vger.kernel.org>,
Matthew Wilcox <matthew@wil.cx>,
Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH] vfs: Fix possible NULL pointer dereference in inode_permission()
Date: Thu, 9 Jan 2014 16:44:11 -0800 [thread overview]
Message-ID: <20140110004411.GS10038@linux.vnet.ibm.com> (raw)
In-Reply-To: <20140109185907.20cddb57@gandalf.local.home>
On Thu, Jan 09, 2014 at 06:59:07PM -0500, Steven Rostedt wrote:
> On Thu, 9 Jan 2014 15:45:37 -0800
> "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
>
> > > static void inode_free_security(struct inode *inode)
> > > {
> > > struct inode_security_struct *isec = inode->i_security;
> > > @@ -244,8 +252,7 @@ static void inode_free_security(struct i
> > > list_del_init(&isec->list);
> > > spin_unlock(&sbsec->isec_lock);
> > >
> > > - inode->i_security = NULL;
> > > - kmem_cache_free(sel_inode_cache, isec);
> > > + call_rcu(&isec->rcu, inode_free_rcu);
> >
> > Does not clearing ->i_security mean that RCU readers can traverse
> > this pointer after the invocation of call_rcu()? If so, this is
> > problematic. (If something else already prevents readers from getting
> > here, no problem.)
>
> This is called when we are about to free the inode. Look at
> destroy_inode(). Basically, this is the same as doing:
>
> call_rcu(&isec->rcu, inode_free_rcu);
> call_rcu(&inode->i_rcu, i_callback);
>
> Where i_callback() does the free of the inode.
>
> If you can access inode->i_security, after a call_rcu, then you can
> also access the inode itself that has just been freed.
>
> Yes, technically, having two separate call_rcu(), the first grace
> period can end before the second, but everything to remove the inode
> from sight has already been set up before that first call_rcu() is
> made. That means when the first call_rcu() is executed, the inode
> should already be invisible to the readers.
Got it, should be fine then, sorry for the noise.
Thanx, Paul
prev parent reply other threads:[~2014-01-10 0:44 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-09 21:27 [PATCH] vfs: Fix possible NULL pointer dereference in inode_permission() Steven Rostedt
2014-01-09 21:42 ` Matthew Wilcox
2014-01-09 21:50 ` Steven Rostedt
2014-01-09 22:31 ` Al Viro
[not found] ` <CA+55aFzCTPYEQCPnLBi1CwmMTocVqCFiCuJ391HkVx1CMw61ug@mail.gmail.com>
2014-01-09 23:10 ` Paul E. McKenney
2014-01-09 23:25 ` Steven Rostedt
2014-01-09 23:27 ` Steven Rostedt
2014-01-09 23:37 ` Eric Paris
2014-01-09 23:45 ` Steven Rostedt
2014-01-09 23:53 ` Linus Torvalds
2014-01-10 0:06 ` Al Viro
2014-01-10 0:09 ` Al Viro
2014-01-10 0:18 ` Linus Torvalds
2014-01-10 2:36 ` James Morris
2014-01-10 9:31 ` Christoph Hellwig
2014-01-10 18:14 ` Ben Myers
2014-01-11 10:32 ` Christoph Hellwig
2014-01-09 23:45 ` Paul E. McKenney
2014-01-09 23:59 ` Steven Rostedt
2014-01-10 0:44 ` Paul E. McKenney [this message]
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