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 <keesc...@chromium.org> Reviewed-by: David Windsor <dwind...@gmail.com> Reviewed-by: Hans Liljestrand <ishkam...@gmail.com> Signed-off-by: Elena Reshetova <elena.reshet...@intel.com> --- 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