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drivers, net, hamradio: convert sixpack.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 sixpack.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 10:23:42 +03:00 committed by David S. Miller
parent dd8e19456d
commit 956cc1e70c
1 changed files with 6 additions and 6 deletions
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12
drivers/net/hamradio/6pack.c
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@ -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