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Commit 709c89b4 authored by Elena Reshetova's avatar Elena Reshetova Committed by David S. Miller
Browse files

drivers, net, ppp: convert syncppp.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 syncppp.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 d780cd44

drivers/net/ppp/ppp_synctty.c

+6 −5
Original line number Diff line number Diff line
@@ -46,6 +46,7 @@ 
#include <linux/init.h>

#include <linux/interrupt.h>

#include <linux/slab.h>

#include <linux/refcount.h>

#include <asm/unaligned.h>

#include <linux/uaccess.h>
@@ -72,7 +73,7 @@ struct syncppp { 


	struct tasklet_struct tsk;



	atomic_t	refcnt;

	refcount_t	refcnt;

	struct completion dead_cmp;

	struct ppp_channel chan;	/* interface to generic ppp layer */

};
@@ -141,14 +142,14 @@ static struct syncppp *sp_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 sp_put(struct syncppp *ap)

{

	if (atomic_dec_and_test(&ap->refcnt))

	if (refcount_dec_and_test(&ap->refcnt))

		complete(&ap->dead_cmp);

}
@@ -182,7 +183,7 @@ ppp_sync_open(struct tty_struct *tty) 
	skb_queue_head_init(&ap->rqueue);

	tasklet_init(&ap->tsk, ppp_sync_process, (unsigned long) ap);



	atomic_set(&ap->refcnt, 1);

	refcount_set(&ap->refcnt, 1);

	init_completion(&ap->dead_cmp);



	ap->chan.private = ap;
@@ -232,7 +233,7 @@ ppp_sync_close(struct tty_struct *tty) 
	 * our channel ops (i.e. ppp_sync_send/ioctl) are in progress

	 * by the time it returns.

	 */

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

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

		wait_for_completion(&ap->dead_cmp);

	tasklet_kill(&ap->tsk);