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drivers, net, ppp: convert asyncppp.refcnt from atomic_t to refcount_t

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atomic_t variables are currently used to implement reference
counters with the following properties:
 - counter is initialized to 1 using atomic_set()
 - a resource is freed upon counter reaching zero
 - once counter reaches zero, its further
   increments aren't allowed
 - counter schema uses basic atomic operations
   (set, inc, inc_not_zero, dec_and_test, etc.)

Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.

The variable asyncppp.refcnt is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Elena Reshetova 2017-10-20 10:23:46 +03:00 committed by David S. Miller
parent 28206cdb3b
commit 313a912155
1 changed files with 5 additions and 5 deletions
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10
drivers/net/ppp/ppp_async.c
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@ -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);