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Date:   Sat, 2 Dec 2023 19:44:24 +0530
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Subject: Re: [syzbot] [net?] [nfc?] KASAN: slab-use-after-free Read in
 nfc_alloc_send_skb
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From:   Siddh Raman Pant <code@siddh.me>
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#syz test https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git main

diff --git a/net/nfc/llcp_core.c b/net/nfc/llcp_core.c
index 1dac28136e6a..e071cb15bce2 100644
--- a/net/nfc/llcp_core.c
+++ b/net/nfc/llcp_core.c
@@ -145,6 +145,12 @@ static void nfc_llcp_socket_release(struct nfc_llcp_local *local, bool device,
 
 static struct nfc_llcp_local *nfc_llcp_local_get(struct nfc_llcp_local *local)
 {
+	struct nfc_dev *d;
+
+	d = nfc_get_device(local->dev->idx);
+	if (!d)
+		return NULL;
+
 	kref_get(&local->ref);
 
 	return local;
@@ -180,6 +186,7 @@ int nfc_llcp_local_put(struct nfc_llcp_local *local)
 	if (local == NULL)
 		return 0;
 
+	nfc_put_device(local->dev);
 	return kref_put(&local->ref, local_release);
 }
 
@@ -959,8 +966,17 @@ static void nfc_llcp_recv_connect(struct nfc_llcp_local *local,
 	}
 
 	new_sock = nfc_llcp_sock(new_sk);
-	new_sock->dev = local->dev;
+
 	new_sock->local = nfc_llcp_local_get(local);
+	if (!new_sock->local) {
+		reason = LLCP_DM_REJ;
+		release_sock(&sock->sk);
+		sock_put(&sock->sk);
+		sock_put(&new_sock->sk);
+		goto fail;
+	}
+
+	new_sock->dev = local->dev;
 	new_sock->rw = sock->rw;
 	new_sock->miux = sock->miux;
 	new_sock->nfc_protocol = sock->nfc_protocol;
@@ -1597,7 +1613,11 @@ int nfc_llcp_register_device(struct nfc_dev *ndev)
 	if (local == NULL)
 		return -ENOMEM;
 
-	local->dev = ndev;
+	/* Hold a reference to the device. */
+	local->dev = nfc_get_device(ndev->idx);
+	if (!local->dev)
+		return -ENODEV;
+
 	INIT_LIST_HEAD(&local->list);
 	kref_init(&local->ref);
 	mutex_init(&local->sdp_lock);