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/key/af_key.c b/net/key/af_key.c
index e466579..edcf1d0 100644
--- a/net/key/af_key.c
+++ b/net/key/af_key.c
@@ -3739,7 +3739,7 @@
 	else
 		seq_printf(f, "%pK %-6d %-6u %-6u %-6u %-6lu\n",
 			       s,
-			       atomic_read(&s->sk_refcnt),
+			       refcount_read(&s->sk_refcnt),
 			       sk_rmem_alloc_get(s),
 			       sk_wmem_alloc_get(s),
 			       from_kuid_munged(seq_user_ns(f), sock_i_uid(s)),