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

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Message-ID: <CAHC9VhQW7xFHBLNQOQRKMftStu_aHjbUmp96VJrcfWzxuzE_kw@mail.gmail.com>
Date:   Mon, 20 Feb 2017 17:07:25 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     Elena Reshetova <elena.reshetova@...el.com>
Cc:     linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-audit@...hat.com, linux-fsdevel@...r.kernel.org,
        peterz@...radead.org, gregkh@...uxfoundation.org,
        viro@...iv.linux.org.uk, tj@...nel.org, mingo@...hat.com,
        hannes@...xchg.org, lizefan@...wei.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, Eric Paris <eparis@...hat.com>,
        akpm@...ux-foundation.org, arnd@...db.de, 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?

> 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