net: convert sock.sk_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.

This patch uses refcount_inc_not_zero() instead of
atomic_inc_not_zero_hint() due to absense of a _hint()
version of refcount API. If the hint() version must
be used, we might need to revisit API.

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>
diff --git a/net/bluetooth/af_bluetooth.c b/net/bluetooth/af_bluetooth.c
index 8a8f77a..91e3ba2 100644
--- a/net/bluetooth/af_bluetooth.c
+++ b/net/bluetooth/af_bluetooth.c
@@ -657,7 +657,7 @@ static int bt_seq_show(struct seq_file *seq, void *v)
 		seq_printf(seq,
 			   "%pK %-6d %-6u %-6u %-6u %-6lu %-6lu",
 			   sk,
-			   atomic_read(&sk->sk_refcnt),
+			   refcount_read(&sk->sk_refcnt),
 			   sk_rmem_alloc_get(sk),
 			   sk_wmem_alloc_get(sk),
 			   from_kuid(seq_user_ns(seq), sock_i_uid(sk)),