linux-kernel - RE: [PATCH 15/19] kernel: convert audit_tree.count from atomic_t to refcount

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Date:   Tue, 21 Feb 2017 07:15:53 +0000
From:   "Reshetova, Elena" <elena.reshetova@...el.com>
To:     Paul Moore <paul@...l-moore.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "linux-audit@...hat.com" <linux-audit@...hat.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "tj@...nel.org" <tj@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hannes@...xchg.org" <hannes@...xchg.org>,
        "lizefan@...wei.com" <lizefan@...wei.com>,
        "acme@...nel.org" <acme@...nel.org>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        Eric Paris <eparis@...hat.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "arnd@...db.de" <arnd@...db.de>,
        "luto@...nel.org" <luto@...nel.org>,
        Hans Liljestrand <ishkamiel@...il.com>,
        Kees Cook <keescook@...omium.org>,
        David Windsor <dwindsor@...il.com>
Subject: RE: [PATCH 15/19] kernel: convert audit_tree.count from atomic_t to
 refcount_t

> On Mon, Feb 20, 2017 at 5:19 AM, Elena Reshetova
> <elena.reshetova@...el.com> wrote:
> > refcount_t type and corresponding API should be
> > used instead of atomic_t when the variable is used as
> > a reference counter. This allows to avoid accidental
> > refcounter overflows that might lead to use-after-free
> > situations.
> >
> > Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
> > Signed-off-by: Hans Liljestrand <ishkamiel@...il.com>
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > Signed-off-by: David Windsor <dwindsor@...il.com>
> > ---
> >  kernel/audit_tree.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> No objection on my end, same for patch 16/19.
> 
> I have no problem merging both these patches into the audit/next
> branch after the merge window, is that your goal or are you merging
> these via a different tree?

Thank you Paul! I think it is better if they go through the trees they supposed to go through
since this way they would get more testing and etc. So, please take the relevant ones to your tree when the time is right. 

After the first round, I guess we will see what patches are not propagating and then maybe take them via Kees tree. 

Best Regards,
Elena.

> 
> > diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c
> > index 7b44195..7ed617b 100644
> > --- a/kernel/audit_tree.c
> > +++ b/kernel/audit_tree.c
> > @@ -9,7 +9,7 @@ struct audit_tree;
> >  struct audit_chunk;
> >
> >  struct audit_tree {
> > -       atomic_t count;
> > +       refcount_t count;
> >         int goner;
> >         struct audit_chunk *root;
> >         struct list_head chunks;
> > @@ -77,7 +77,7 @@ static struct audit_tree *alloc_tree(const char *s)
> >
> >         tree = kmalloc(sizeof(struct audit_tree) + strlen(s) + 1, GFP_KERNEL);
> >         if (tree) {
> > -               atomic_set(&tree->count, 1);
> > +               refcount_set(&tree->count, 1);
> >                 tree->goner = 0;
> >                 INIT_LIST_HEAD(&tree->chunks);
> >                 INIT_LIST_HEAD(&tree->rules);
> > @@ -91,12 +91,12 @@ static struct audit_tree *alloc_tree(const char *s)
> >
> >  static inline void get_tree(struct audit_tree *tree)
> >  {
> > -       atomic_inc(&tree->count);
> > +       refcount_inc(&tree->count);
> >  }
> >
> >  static inline void put_tree(struct audit_tree *tree)
> >  {
> > -       if (atomic_dec_and_test(&tree->count))
> > +       if (refcount_dec_and_test(&tree->count))
> >                 kfree_rcu(tree, head);
> >  }
> >
> 
> --
> paul moore
> www.paul-moore.com