xfrm_user: fix freeing of xfrm states on acquire

Commit 565f0fa9 ("xfrm: use a dedicated slab cache for struct
xfrm_state") moved xfrm state objects to use their own slab cache.
However, it missed to adapt xfrm_user to use this new cache when
freeing xfrm states.

Fix this by introducing and make use of a new helper for freeing
xfrm_state objects.

Fixes: 565f0fa9 ("xfrm: use a dedicated slab cache for struct xfrm_state")
Reported-by: Pan Bian <bianpan2016@163.com>
Cc: <stable@vger.kernel.org> # v4.18+
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

include/net/xfrm.h

@@ -1552,6 +1552,7 @@ int xfrm_state_walk(struct net *net, struct xfrm_state_walk *walk,
 		    int (*func)(struct xfrm_state *, int, void*), void *);
 void xfrm_state_walk_done(struct xfrm_state_walk *walk, struct net *net);
 struct xfrm_state *xfrm_state_alloc(struct net *net);
+void xfrm_state_free(struct xfrm_state *x);
 struct xfrm_state *xfrm_state_find(const xfrm_address_t *daddr,
 				   const xfrm_address_t *saddr,
 				   const struct flowi *fl,

net/xfrm/xfrm_state.c

@@ -426,6 +426,12 @@ static void xfrm_put_mode(struct xfrm_mode *mode)
 	module_put(mode->owner);
 }
 
+void xfrm_state_free(struct xfrm_state *x)
+{
+	kmem_cache_free(xfrm_state_cache, x);
+}
+EXPORT_SYMBOL(xfrm_state_free);
+
 static void xfrm_state_gc_destroy(struct xfrm_state *x)
 {
 	tasklet_hrtimer_cancel(&x->mtimer);
@@ -452,7 +458,7 @@ static void xfrm_state_gc_destroy(struct xfrm_state *x)
 	}
 	xfrm_dev_state_free(x);
 	security_xfrm_state_free(x);
-	kmem_cache_free(xfrm_state_cache, x);
+	xfrm_state_free(x);
 }
 
 static void xfrm_state_gc_task(struct work_struct *work)

net/xfrm/xfrm_user.c

@@ -2288,13 +2288,13 @@ static int xfrm_add_acquire(struct sk_buff *skb, struct nlmsghdr *nlh,
 
 	}
 
-	kfree(x);
+	xfrm_state_free(x);
 	kfree(xp);
 
 	return 0;
 
 free_state:
-	kfree(x);
+	xfrm_state_free(x);
 nomem:
 	return err;
 }