From 709c89b45b874b2f81a074b8802a736009873f48 Mon Sep 17 00:00:00 2001 From: Elena Reshetova Date: Fri, 20 Oct 2017 10:23:48 +0300 Subject: drivers, net, ppp: convert syncppp.refcnt from atomic_t to refcount_t 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 Reviewed-by: David Windsor Reviewed-by: Hans Liljestrand Signed-off-by: Elena Reshetova Signed-off-by: David S. Miller --- drivers/net/ppp/ppp_synctty.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/drivers/net/ppp/ppp_synctty.c b/drivers/net/ppp/ppp_synctty.c index 7868c29071d4..7196f00f0991 100644 --- a/drivers/net/ppp/ppp_synctty.c +++ b/drivers/net/ppp/ppp_synctty.c @@ -46,6 +46,7 @@ #include #include #include +#include #include #include @@ -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); -- cgit v1.2.3