net, ipv6: convert ipv6_txoptions.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>

include/net/ipv6.h

@@ -16,6 +16,7 @@
 #include <linux/ipv6.h>
 #include <linux/hardirq.h>
 #include <linux/jhash.h>
+#include <linux/refcount.h>
 #include <net/if_inet6.h>
 #include <net/ndisc.h>
 #include <net/flow.h>
@@ -203,7 +204,7 @@ extern rwlock_t ip6_ra_lock;
  */
 
 struct ipv6_txoptions {
-	atomic_t		refcnt;
+	refcount_t		refcnt;
 	/* Length of this structure */
 	int			tot_len;
 
@@ -265,7 +266,7 @@ static inline struct ipv6_txoptions *txopt_get(const struct ipv6_pinfo *np)
 	rcu_read_lock();
 	opt = rcu_dereference(np->opt);
 	if (opt) {
-		if (!atomic_inc_not_zero(&opt->refcnt))
+		if (!refcount_inc_not_zero(&opt->refcnt))
 			opt = NULL;
 		else
 			opt = rcu_pointer_handoff(opt);
@@ -276,7 +277,7 @@ static inline struct ipv6_txoptions *txopt_get(const struct ipv6_pinfo *np)
 
 static inline void txopt_put(struct ipv6_txoptions *opt)
 {
-	if (opt && atomic_dec_and_test(&opt->refcnt))
+	if (opt && refcount_dec_and_test(&opt->refcnt))
 		kfree_rcu(opt, rcu);
 }
 

net/ipv6/exthdrs.c

@@ -971,7 +971,7 @@ ipv6_dup_options(struct sock *sk, struct ipv6_txoptions *opt)
 			*((char **)&opt2->dst1opt) += dif;
 		if (opt2->srcrt)
 			*((char **)&opt2->srcrt) += dif;
-		atomic_set(&opt2->refcnt, 1);
+		refcount_set(&opt2->refcnt, 1);
 	}
 	return opt2;
 }
@@ -1056,7 +1056,7 @@ ipv6_renew_options(struct sock *sk, struct ipv6_txoptions *opt,
 		return ERR_PTR(-ENOBUFS);
 
 	memset(opt2, 0, tot_len);
-	atomic_set(&opt2->refcnt, 1);
+	refcount_set(&opt2->refcnt, 1);
 	opt2->tot_len = tot_len;
 	p = (char *)(opt2 + 1);
 

net/ipv6/ipv6_sockglue.c

@@ -505,7 +505,7 @@ sticky_done:
 			break;
 
 		memset(opt, 0, sizeof(*opt));
-		atomic_set(&opt->refcnt, 1);
+		refcount_set(&opt->refcnt, 1);
 		opt->tot_len = sizeof(*opt) + optlen;
 		retv = -EFAULT;
 		if (copy_from_user(opt+1, optval, optlen))