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drivers, net, ppp: convert ppp_file.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 ppp_file.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 10:23:47 +03:00 committed by David S. Miller
parent 313a912155
commit d780cd44e3
1 changed files with 11 additions and 10 deletions
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21
drivers/net/ppp/ppp_generic.c
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@ -51,6 +51,7 @@
#include <asm/unaligned.h>
#include <net/slhc_vj.h>
#include <linux/atomic.h>
#include <linux/refcount.h>
#include <linux/nsproxy.h>
#include <net/net_namespace.h>
@ -84,7 +85,7 @@ struct ppp_file {
struct sk_buff_head xq; /* pppd transmit queue */
struct sk_buff_head rq; /* receive queue for pppd */
wait_queue_head_t rwait; /* for poll on reading /dev/ppp */
atomic_t refcnt; /* # refs (incl /dev/ppp attached) */
refcount_t refcnt; /* # refs (incl /dev/ppp attached) */
int hdrlen; /* space to leave for headers */
int index; /* interface unit / channel number */
int dead; /* unit/channel has been shut down */
@ -408,7 +409,7 @@ static int ppp_release(struct inode *unused, struct file *file)
unregister_netdevice(ppp->dev);
rtnl_unlock();
}
if (atomic_dec_and_test(&pf->refcnt)) {
if (refcount_dec_and_test(&pf->refcnt)) {
switch (pf->kind) {
case INTERFACE:
ppp_destroy_interface(PF_TO_PPP(pf));
@ -881,7 +882,7 @@ static int ppp_unattached_ioctl(struct net *net, struct ppp_file *pf,
mutex_lock(&pn->all_ppp_mutex);
ppp = ppp_find_unit(pn, unit);
if (ppp) {
atomic_inc(&ppp->file.refcnt);
refcount_inc(&ppp->file.refcnt);
file->private_data = &ppp->file;
err = 0;
}
@ -896,7 +897,7 @@ static int ppp_unattached_ioctl(struct net *net, struct ppp_file *pf,
spin_lock_bh(&pn->all_channels_lock);
chan = ppp_find_channel(pn, unit);
if (chan) {
atomic_inc(&chan->file.refcnt);
refcount_inc(&chan->file.refcnt);
file->private_data = &chan->file;
err = 0;
}
@ -1348,7 +1349,7 @@ static int ppp_dev_init(struct net_device *dev)
* that ppp_destroy_interface() won't run before the device gets
* unregistered.
*/
atomic_inc(&ppp->file.refcnt);
refcount_inc(&ppp->file.refcnt);
return 0;
}
@ -1377,7 +1378,7 @@ static void ppp_dev_priv_destructor(struct net_device *dev)
struct ppp *ppp;
ppp = netdev_priv(dev);
if (atomic_dec_and_test(&ppp->file.refcnt))
if (refcount_dec_and_test(&ppp->file.refcnt))
ppp_destroy_interface(ppp);
}
@ -2676,7 +2677,7 @@ ppp_unregister_channel(struct ppp_channel *chan)
pch->file.dead = 1;
wake_up_interruptible(&pch->file.rwait);
if (atomic_dec_and_test(&pch->file.refcnt))
if (refcount_dec_and_test(&pch->file.refcnt))
ppp_destroy_channel(pch);
}
@ -3046,7 +3047,7 @@ init_ppp_file(struct ppp_file *pf, int kind)
pf->kind = kind;
skb_queue_head_init(&pf->xq);
skb_queue_head_init(&pf->rq);
atomic_set(&pf->refcnt, 1);
refcount_set(&pf->refcnt, 1);
init_waitqueue_head(&pf->rwait);
}
@ -3164,7 +3165,7 @@ ppp_connect_channel(struct channel *pch, int unit)
list_add_tail(&pch->clist, &ppp->channels);
++ppp->n_channels;
pch->ppp = ppp;
atomic_inc(&ppp->file.refcnt);
refcount_inc(&ppp->file.refcnt);
ppp_unlock(ppp);
ret = 0;
@ -3195,7 +3196,7 @@ ppp_disconnect_channel(struct channel *pch)
if (--ppp->n_channels == 0)
wake_up_interruptible(&ppp->file.rwait);
ppp_unlock(ppp);
if (atomic_dec_and_test(&ppp->file.refcnt))
if (refcount_dec_and_test(&ppp->file.refcnt))
ppp_destroy_interface(ppp);
err = 0;
}