Re: [PATCH 3/3] ipc: convert ipc_rcu.refcount from atomic_t to refcount_t

[Kees Cook]

On Mon, Feb 20, 2017 at 3:29 AM, Elena Reshetova
<elena.reshetova@xxxxxxxxx> 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@xxxxxxxxx>
> Signed-off-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Signed-off-by: David Windsor <dwindsor@xxxxxxxxx>

After the IPC RCU refactoring, this needs rework... I'll send a new patch...

-Kees

> ---
>  ipc/util.c | 6 +++---
>  ipc/util.h | 3 ++-
>  2 files changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/ipc/util.c b/ipc/util.c
> index 798cad1..24484a6 100644
> --- a/ipc/util.c
> +++ b/ipc/util.c
> @@ -437,7 +437,7 @@ void *ipc_rcu_alloc(int size)
>         struct ipc_rcu *out = ipc_alloc(sizeof(struct ipc_rcu) + size);
>         if (unlikely(!out))
>                 return NULL;
> -       atomic_set(&out->refcount, 1);
> +       refcount_set(&out->refcount, 1);
>         return out + 1;
>  }
>
> @@ -445,14 +445,14 @@ int ipc_rcu_getref(void *ptr)
>  {
>         struct ipc_rcu *p = ((struct ipc_rcu *)ptr) - 1;
>
> -       return atomic_inc_not_zero(&p->refcount);
> +       return refcount_inc_not_zero(&p->refcount);
>  }
>
>  void ipc_rcu_putref(void *ptr, void (*func)(struct rcu_head *head))
>  {
>         struct ipc_rcu *p = ((struct ipc_rcu *)ptr) - 1;
>
> -       if (!atomic_dec_and_test(&p->refcount))
> +       if (!refcount_dec_and_test(&p->refcount))
>                 return;
>
>         call_rcu(&p->rcu, func);
> diff --git a/ipc/util.h b/ipc/util.h
> index 51f7ca5..274ec9b 100644
> --- a/ipc/util.h
> +++ b/ipc/util.h
> @@ -12,6 +12,7 @@
>
>  #include <linux/unistd.h>
>  #include <linux/err.h>
> +#include <linux/refcount.h>
>
>  #define SEQ_MULTIPLIER (IPCMNI)
>
> @@ -49,7 +50,7 @@ static inline void shm_exit_ns(struct ipc_namespace *ns) { }
>
>  struct ipc_rcu {
>         struct rcu_head rcu;
> -       atomic_t refcount;
> +       refcount_t refcount;
>  } ____cacheline_aligned_in_smp;
>
>  #define ipc_rcu_to_struct(p)  ((void *)(p+1))
> --
> 2.7.4
>



-- 
Kees Cook
Pixel Security