net: convert ip_mc_list.refcnt from atomic_t to refcount_t

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.reshetova@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 7 insertions, 6 deletions

diff --git a/include/linux/igmp.h b/include/linux/igmp.h
index 12f6fba6d21a..97caf1821de8 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 c4032302d7cd..28f14afd0dd3 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);