netdev - [PATCH v2 net-next 2/2] net: convert (struct ubuf_info)->refcnt to refcount

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Message-Id: <20170831234822.26612-3-edumazet@google.com>
Date:   Thu, 31 Aug 2017 16:48:22 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: [PATCH v2 net-next 2/2] net: convert (struct ubuf_info)->refcnt 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.

v2: added the change in drivers/vhost/net.c as spotted
by Willem.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 drivers/vhost/net.c    | 2 +-
 include/linux/skbuff.h | 5 +++--
 net/core/skbuff.c      | 6 +++---
 3 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index ba08b78ed630c429ccf415af69bf27f2433af4f0..8d2bcae53a2ec9ea1c876625e581bcd429abe365 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -533,7 +533,7 @@ static void handle_tx(struct vhost_net *net)
 			ubuf->callback = vhost_zerocopy_callback;
 			ubuf->ctx = nvq->ubufs;
 			ubuf->desc = nvq->upend_idx;
-			atomic_set(&ubuf->refcnt, 1);
+			refcount_set(&ubuf->refcnt, 1);
 			msg.msg_control = ubuf;
 			msg.msg_controllen = sizeof(ubuf);
 			ubufs = nvq->ubufs;
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 7594e19bce622a38dc39c054093c3da15b99b67b..316a92b45351f53709886ee0099cbc83b66f1b15 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -22,6 +22,7 @@
 #include <linux/cache.h>
 #include <linux/rbtree.h>
 #include <linux/socket.h>
+#include <linux/refcount.h>
 
 #include <linux/atomic.h>
 #include <asm/types.h>
@@ -456,7 +457,7 @@ struct ubuf_info {
 			u32 bytelen;
 		};
 	};
-	atomic_t refcnt;
+	refcount_t refcnt;
 
 	struct mmpin {
 		struct user_struct *user;
@@ -472,7 +473,7 @@ struct ubuf_info *sock_zerocopy_realloc(struct sock *sk, size_t size,
 
 static inline void sock_zerocopy_get(struct ubuf_info *uarg)
 {
-	atomic_inc(&uarg->refcnt);
+	refcount_inc(&uarg->refcnt);
 }
 
 void sock_zerocopy_put(struct ubuf_info *uarg);
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 1a754d7896ceac1eb85e3b13c1422b4d6a88fedf..06b9ddca3188442d1d1d2052fc060cf5b1e2a6f4 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -963,7 +963,7 @@ struct ubuf_info *sock_zerocopy_alloc(struct sock *sk, size_t size)
 	uarg->len = 1;
 	uarg->bytelen = size;
 	uarg->zerocopy = 1;
-	atomic_set(&uarg->refcnt, 1);
+	refcount_set(&uarg->refcnt, 1);
 	sock_hold(sk);
 
 	return uarg;
@@ -1086,7 +1086,7 @@ EXPORT_SYMBOL_GPL(sock_zerocopy_callback);
 
 void sock_zerocopy_put(struct ubuf_info *uarg)
 {
-	if (uarg && atomic_dec_and_test(&uarg->refcnt)) {
+	if (uarg && refcount_dec_and_test(&uarg->refcnt)) {
 		if (uarg->callback)
 			uarg->callback(uarg, uarg->zerocopy);
 		else
@@ -1483,7 +1483,7 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
 		if (skb_orphan_frags(skb, gfp_mask))
 			goto nofrags;
 		if (skb_zcopy(skb))
-			atomic_inc(&skb_uarg(skb)->refcnt);
+			refcount_inc(&skb_uarg(skb)->refcnt);
 		for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
 			skb_frag_ref(skb, i);
 
-- 
2.14.1.581.gf28d330327-goog