On Thu, Jan 09, 2014 at 06:27:56PM -0500, Steven Rostedt wrote:
> On Thu, 9 Jan 2014 18:25:23 -0500
> Steven Rostedt <[email protected]> wrote:
>
> > On Fri, 10 Jan 2014 06:41:03 +0800
> > Linus Torvalds <[email protected]> wrote:
> >
> > > I think the sane short term fix is to make the kfree() of the i_security
> > > member be a rcu free, and not clear the member.
> >
> > You mean my first patch?
> >
> > https://lkml.org/lkml/2014/1/9/349
> >
>
> Oh wait, you said not to clear the member. Thus, the patch would look
> like this:
>
> Signed-off-by: Steven Rostedt <[email protected]>
>
> Index: linux-trace.git/security/selinux/hooks.c
> ===================================================================
> --- linux-trace.git.orig/security/selinux/hooks.c
> +++ linux-trace.git/security/selinux/hooks.c
> @@ -234,6 +234,14 @@ static int inode_alloc_security(struct i
> return 0;
> }
>
> +static void inode_free_rcu(struct rcu_head *head)
> +{
> + struct inode_security_struct *isec;
> +
> + isec = container_of(head, struct inode_security_struct, rcu);
> + kmem_cache_free(sel_inode_cache, isec);
> +}
> +
> 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.)
Thanx, Paul
> }
>
> static int file_alloc_security(struct file *file)
> Index: linux-trace.git/security/selinux/include/objsec.h
> ===================================================================
> --- linux-trace.git.orig/security/selinux/include/objsec.h
> +++ linux-trace.git/security/selinux/include/objsec.h
> @@ -38,7 +38,10 @@ struct task_security_struct {
>
> struct inode_security_struct {
> struct inode *inode; /* back pointer to inode object */
> - struct list_head list; /* list of inode_security_struct */
> + union {
> + struct list_head list; /* list of inode_security_struct */
> + struct rcu_head rcu; /* for freeing the
> inode_security_struct */
> + };
> u32 task_sid; /* SID of creating task */
> u32 sid; /* SID of this object */
> u16 sclass; /* security class of this object */
>
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