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Commit 956cc1e7 authored by Elena Reshetova's avatar Elena Reshetova Committed by David S. Miller
Browse files

drivers, net, hamradio: convert sixpack.refcnt from atomic_t to refcount_t 



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

Suggested-by: default avatarKees Cook <keescook@chromium.org>
Reviewed-by: default avatarDavid Windsor <dwindsor@gmail.com>
Reviewed-by: default avatarHans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: default avatarElena Reshetova <elena.reshetova@intel.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent dd8e1945

drivers/net/hamradio/6pack.c

+6 −6
Original line number Diff line number Diff line
@@ -35,7 +35,7 @@ 
#include <linux/tcp.h>

#include <linux/semaphore.h>

#include <linux/compat.h>

#include <linux/atomic.h>

#include <linux/refcount.h>



#define SIXPACK_VERSION    "Revision: 0.3.0"
@@ -120,7 +120,7 @@ struct sixpack { 


	struct timer_list	tx_t;

	struct timer_list	resync_t;

	atomic_t		refcnt;

	refcount_t		refcnt;

	struct semaphore	dead_sem;

	spinlock_t		lock;

};
@@ -381,7 +381,7 @@ static struct sixpack *sp_get(struct tty_struct *tty) 
	read_lock(&disc_data_lock);

	sp = tty->disc_data;

	if (sp)

		atomic_inc(&sp->refcnt);

		refcount_inc(&sp->refcnt);

	read_unlock(&disc_data_lock);



	return sp;
@@ -389,7 +389,7 @@ static struct sixpack *sp_get(struct tty_struct *tty) 


static void sp_put(struct sixpack *sp)

{

	if (atomic_dec_and_test(&sp->refcnt))

	if (refcount_dec_and_test(&sp->refcnt))

		up(&sp->dead_sem);

}
@@ -576,7 +576,7 @@ static int sixpack_open(struct tty_struct *tty) 
	sp->dev = dev;



	spin_lock_init(&sp->lock);

	atomic_set(&sp->refcnt, 1);

	refcount_set(&sp->refcnt, 1);

	sema_init(&sp->dead_sem, 0);



	/* !!! length of the buffers. MTU is IP MTU, not PACLEN!  */
@@ -670,7 +670,7 @@ static void sixpack_close(struct tty_struct *tty) 
	 * We have now ensured that nobody can start using ap from now on, but

	 * we have to wait for all existing users to finish.

	 */

	if (!atomic_dec_and_test(&sp->refcnt))

	if (!refcount_dec_and_test(&sp->refcnt))

		down(&sp->dead_sem);



	/* We must stop the queue to avoid potentially scribbling