[PATCH 09/17] net: convert ip_mc_list.refcnt from atomic_t to refcount_t

[Elena Reshetova]

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshet...@intel.com>
Signed-off-by: Hans Liljestrand <ishkam...@gmail.com>
Signed-off-by: Kees Cook <keesc...@chromium.org>
Signed-off-by: David Windsor <dwind...@gmail.com>
---
 include/linux/igmp.h |  3 ++-
 net/ipv4/igmp.c      | 10 +++++-----
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/include/linux/igmp.h b/include/linux/igmp.h
index 12f6fba..97caf18 100644
--- a/include/linux/igmp.h
+++ b/include/linux/igmp.h
@@ -18,6 +18,7 @@
 #include <linux/skbuff.h>
 #include <linux/timer.h>
 #include <linux/in.h>
+#include <linux/refcount.h>
 #include <uapi/linux/igmp.h>
 
 static inline struct igmphdr *igmp_hdr(const struct sk_buff *skb)
@@ -84,7 +85,7 @@ struct ip_mc_list {
        struct ip_mc_list __rcu *next_hash;
        struct timer_list       timer;
        int                     users;
-       atomic_t                refcnt;
+       refcount_t              refcnt;
        spinlock_t              lock;
        char                    tm_running;
        char                    reporter;
diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index ec9a396..f7685f7 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -173,7 +173,7 @@ static int ip_mc_add_src(struct in_device *in_dev, __be32 
*pmca, int sfmode,
 
 static void ip_ma_put(struct ip_mc_list *im)
 {
-       if (atomic_dec_and_test(&im->refcnt)) {
+       if (refcount_dec_and_test(&im->refcnt)) {
                in_dev_put(im->interface);
                kfree_rcu(im, rcu);
        }
@@ -199,7 +199,7 @@ static void igmp_stop_timer(struct ip_mc_list *im)
 {
        spin_lock_bh(&im->lock);
        if (del_timer(&im->timer))
-               atomic_dec(&im->refcnt);
+               refcount_dec(&im->refcnt);
        im->tm_running = 0;
        im->reporter = 0;
        im->unsolicit_count = 0;
@@ -213,7 +213,7 @@ static void igmp_start_timer(struct ip_mc_list *im, int 
max_delay)
 
        im->tm_running = 1;
        if (!mod_timer(&im->timer, jiffies+tv+2))
-               atomic_inc(&im->refcnt);
+               refcount_inc(&im->refcnt);
 }
 
 static void igmp_gq_start_timer(struct in_device *in_dev)
@@ -249,7 +249,7 @@ static void igmp_mod_timer(struct ip_mc_list *im, int 
max_delay)
                        spin_unlock_bh(&im->lock);
                        return;
                }
-               atomic_dec(&im->refcnt);
+               refcount_dec(&im->refcnt);
        }
        igmp_start_timer(im, max_delay);
        spin_unlock_bh(&im->lock);
@@ -1374,7 +1374,7 @@ void ip_mc_inc_group(struct in_device *in_dev, __be32 
addr)
        /* initial mode is (EX, empty) */
        im->sfmode = MCAST_EXCLUDE;
        im->sfcount[MCAST_EXCLUDE] = 1;
-       atomic_set(&im->refcnt, 1);
+       refcount_set(&im->refcnt, 1);
        spin_lock_init(&im->lock);
 #ifdef CONFIG_IP_MULTICAST
        setup_timer(&im->timer, igmp_timer_expire, (unsigned long)im);
-- 
2.7.4