packet: Move reference count in packet_sock to atomic_long_t

In some potential instances the reference count on struct packet_sock
could be saturated and cause overflows which gets the kernel a bit
confused. To prevent this, move to a 64-bit atomic reference count on
64-bit architectures to prevent the possibility of this type to overflow.

Because we can not handle saturation, using refcount_t is not possible
in this place. Maybe someday in the future if it changes it could be
used. Also, instead of using plain atomic64_t, use atomic_long_t instead.
32-bit machines tend to be memory-limited (i.e. anything that increases
a reference uses so much memory that you can't actually get to 2**32
references). 32-bit architectures also tend to have serious problems
with 64-bit atomics. Hence, atomic_long_t is the more natural solution.

Reported-by: "The UK's National Cyber Security Centre (NCSC)" <[e-mail]>
Co-developed-by: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: [e-mail]
Reviewed-by: Willem de Bruijn <[e-mail]>
Reviewed-by: Eric Dumazet <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

net/packet/af_packet.c

···
 	struct sock *sk = sock->sk;
 
 	if (sk)
-		atomic_inc(&pkt_sk(sk)->mapped);
+		atomic_long_inc(&pkt_sk(sk)->mapped);
 }
 
 static void packet_mm_close(struct vm_area_struct *vma)
···
 	struct sock *sk = sock->sk;
 
 	if (sk)
-		atomic_dec(&pkt_sk(sk)->mapped);
+		atomic_long_dec(&pkt_sk(sk)->mapped);
 }
 
 static const struct vm_operations_struct packet_mmap_ops = {
···
 
 	err = -EBUSY;
 	if (!closing) {
-		if (atomic_read(&po->mapped))
+		if (atomic_long_read(&po->mapped))
 			goto out;
 		if (packet_read_pending(rb))
 			goto out;
···
 
 	err = -EBUSY;
 	mutex_lock(&po->pg_vec_lock);
-	if (closing || atomic_read(&po->mapped) == 0) {
+	if (closing || atomic_long_read(&po->mapped) == 0) {
 		err = 0;
 		spin_lock_bh(&rb_queue->lock);
 		swap(rb->pg_vec, pg_vec);
···
 		po->prot_hook.func = (po->rx_ring.pg_vec) ?
 						tpacket_rcv : packet_rcv;
 		skb_queue_purge(rb_queue);
-		if (atomic_read(&po->mapped))
-			pr_err("packet_mmap: vma is busy: %d\n",
-			       atomic_read(&po->mapped));
+		if (atomic_long_read(&po->mapped))
+			pr_err("packet_mmap: vma is busy: %ld\n",
+			       atomic_long_read(&po->mapped));
 	}
 	mutex_unlock(&po->pg_vec_lock);
 
···
 		}
 	}
 
-	atomic_inc(&po->mapped);
+	atomic_long_inc(&po->mapped);
 	vma->vm_ops = &packet_mmap_ops;
 	err = 0;
 

net/packet/internal.h

···
 	__be16			num;
 	struct packet_rollover	*rollover;
 	struct packet_mclist	*mclist;
-	atomic_t		mapped;
+	atomic_long_t		mapped;
 	enum tpacket_versions	tp_version;
 	unsigned int		tp_hdrlen;
 	unsigned int		tp_reserve;