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drivers, net, ppp: convert syncppp.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 syncppp.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 10:23:48 +03:00 committed by David S. Miller
parent d780cd44e3
commit 709c89b45b
1 changed files with 6 additions and 5 deletions
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11
drivers/net/ppp/ppp_synctty.c
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@ -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);