[PATCH 12/16] drivers, net, ppp: convert asyncppp.refcnt from atomic_t to refcount_t

[Elena Reshetova]

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.reshet...@intel.com>
Signed-off-by: Hans Liljestrand <ishkam...@gmail.com>
Signed-off-by: Kees Cook <keesc...@chromium.org>
Signed-off-by: David Windsor <dwind...@gmail.com>
---
 drivers/net/ppp/ppp_async.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ppp/ppp_async.c b/drivers/net/ppp/ppp_async.c
index feb9569..2d08f7e 100644
--- a/drivers/net/ppp/ppp_async.c
+++ b/drivers/net/ppp/ppp_async.c
@@ -69,7 +69,7 @@ struct asyncppp {
 
        struct tasklet_struct tsk;
 
-       atomic_t        refcnt;
+       refcount_t      refcnt;
        struct semaphore dead_sem;
        struct ppp_channel chan;        /* interface to generic ppp layer */
        unsigned char   obuf[OBUFSIZE];
@@ -140,14 +140,14 @@ static struct asyncppp *ap_get(struct tty_struct *tty)
        read_lock(&disc_data_lock);
        ap = tty->disc_data;
        if (ap != NULL)
-               atomic_inc(&ap->refcnt);
+               refcount_inc(&ap->refcnt);
        read_unlock(&disc_data_lock);
        return ap;
 }
 
 static void ap_put(struct asyncppp *ap)
 {
-       if (atomic_dec_and_test(&ap->refcnt))
+       if (refcount_dec_and_test(&ap->refcnt))
                up(&ap->dead_sem);
 }
 
@@ -185,7 +185,7 @@ ppp_asynctty_open(struct tty_struct *tty)
        skb_queue_head_init(&ap->rqueue);
        tasklet_init(&ap->tsk, ppp_async_process, (unsigned long) ap);
 
-       atomic_set(&ap->refcnt, 1);
+       refcount_set(&ap->refcnt, 1);
        sema_init(&ap->dead_sem, 0);
 
        ap->chan.private = ap;
@@ -234,7 +234,7 @@ ppp_asynctty_close(struct tty_struct *tty)
         * our channel ops (i.e. ppp_async_send/ioctl) are in progress
         * by the time it returns.
         */
-       if (!atomic_dec_and_test(&ap->refcnt))
+       if (!refcount_dec_and_test(&ap->refcnt))
                down(&ap->dead_sem);
        tasklet_kill(&ap->tsk);
 
-- 
2.7.4