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@xxxxxxxxxxxx>
Reviewed-by: David Windsor <dwindsor@xxxxxxxxx>
Reviewed-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
Signed-off-by: Elena Reshetova <elena.reshetova@xxxxxxxxx>
---
drivers/net/ppp/ppp_generic.c | 21 +++++++++++----------
1 file changed, 11 insertions(+), 10 deletions(-)
diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
index e365866..6566107 100644
--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -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;
}
--
2.7.4
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