On Mon, Feb 20, 2017 at 3:29 AM, Elena Reshetova
<[email protected]> 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 <[email protected]>
> Signed-off-by: Hans Liljestrand <[email protected]>
> Signed-off-by: Kees Cook <[email protected]>
> Signed-off-by: David Windsor <[email protected]>
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
