linux-kernel - Re: [PATCH 1/3] ipc: convert ipc_namespace.count from atomic_t to refcount

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Message-ID: <CAGXu5jKx+CXvEWVxbSM7awa5+yE8aS3dNXyi89tbitzX2EPhPg@mail.gmail.com>
Date:   Sat, 27 May 2017 12:41:47 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Manfred Spraul <manfred@...orfullife.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Ingo Molnar <mingo@...hat.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        "Serge E. Hallyn" <serge@...lyn.com>, arozansk@...hat.com,
        Davidlohr Bueso <dave@...olabs.net>,
        Hans Liljestrand <ishkamiel@...il.com>,
        David Windsor <dwindsor@...il.com>
Subject: Re: [PATCH 1/3] ipc: convert ipc_namespace.count from atomic_t to refcount_t

On Mon, Feb 20, 2017 at 3:29 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>

Manfred, is this okay by you? I think this should go via -mm...

-Kees

> ---
>  include/linux/ipc_namespace.h | 5 +++--
>  ipc/msgutil.c                 | 2 +-
>  ipc/namespace.c               | 4 ++--
>  3 files changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h
> index 848e579..7230638 100644
> --- a/include/linux/ipc_namespace.h
> +++ b/include/linux/ipc_namespace.h
> @@ -7,6 +7,7 @@
>  #include <linux/notifier.h>
>  #include <linux/nsproxy.h>
>  #include <linux/ns_common.h>
> +#include <linux/refcount.h>
>
>  struct user_namespace;
>
> @@ -19,7 +20,7 @@ struct ipc_ids {
>  };
>
>  struct ipc_namespace {
> -       atomic_t        count;
> +       refcount_t      count;
>         struct ipc_ids  ids[3];
>
>         int             sem_ctls[4];
> @@ -118,7 +119,7 @@ extern struct ipc_namespace *copy_ipcs(unsigned long flags,
>  static inline struct ipc_namespace *get_ipc_ns(struct ipc_namespace *ns)
>  {
>         if (ns)
> -               atomic_inc(&ns->count);
> +               refcount_inc(&ns->count);
>         return ns;
>  }
>
> diff --git a/ipc/msgutil.c b/ipc/msgutil.c
> index bf74eaa..8459802 100644
> --- a/ipc/msgutil.c
> +++ b/ipc/msgutil.c
> @@ -29,7 +29,7 @@ DEFINE_SPINLOCK(mq_lock);
>   * and not CONFIG_IPC_NS.
>   */
>  struct ipc_namespace init_ipc_ns = {
> -       .count          = ATOMIC_INIT(1),
> +       .count          = REFCOUNT_INIT(1),
>         .user_ns = &init_user_ns,
>         .ns.inum = PROC_IPC_INIT_INO,
>  #ifdef CONFIG_IPC_NS
> diff --git a/ipc/namespace.c b/ipc/namespace.c
> index 0abdea4..ed10bbc 100644
> --- a/ipc/namespace.c
> +++ b/ipc/namespace.c
> @@ -48,7 +48,7 @@ static struct ipc_namespace *create_ipc_ns(struct user_namespace *user_ns,
>                 goto fail_free;
>         ns->ns.ops = &ipcns_operations;
>
> -       atomic_set(&ns->count, 1);
> +       refcount_set(&ns->count, 1);
>         ns->user_ns = get_user_ns(user_ns);
>         ns->ucounts = ucounts;
>
> @@ -142,7 +142,7 @@ static void free_ipc_ns(struct ipc_namespace *ns)
>   */
>  void put_ipc_ns(struct ipc_namespace *ns)
>  {
> -       if (atomic_dec_and_lock(&ns->count, &mq_lock)) {
> +       if (refcount_dec_and_lock(&ns->count, &mq_lock)) {
>                 mq_clear_sbinfo(ns);
>                 spin_unlock(&mq_lock);
>                 mq_put_mnt(ns);
> --
> 2.7.4
>



-- 
Kees Cook
Pixel Security