net: ioctl: Use kernel memory on protocol ioctl callbacks

Most of the ioctls to net protocols operates directly on userspace
argument (arg). Usually doing get_user()/put_user() directly in the
ioctl callback.  This is not flexible, because it is hard to reuse these
functions without passing userspace buffers.

Change the "struct proto" ioctls to avoid touching userspace memory and
operate on kernel buffers, i.e., all protocol's ioctl callbacks is
adapted to operate on a kernel memory other than on userspace (so, no
more {put,get}_user() and friends being called in the ioctl callback).

This changes the "struct proto" ioctl format in the following way:

    int                     (*ioctl)(struct sock *sk, int cmd,
-                                        unsigned long arg);
+                                        int *karg);

(Important to say that this patch does not touch the "struct proto_ops"
protocols)

So, the "karg" argument, which is passed to the ioctl callback, is a
pointer allocated to kernel space memory (inside a function wrapper).
This buffer (karg) may contain input argument (copied from userspace in
a prep function) and it might return a value/buffer, which is copied
back to userspace if necessary. There is not one-size-fits-all format
(that is I am using 'may' above), but basically, there are three type of
ioctls:

1) Do not read from userspace, returns a result to userspace
2) Read an input parameter from userspace, and does not return anything
  to userspace
3) Read an input from userspace, and return a buffer to userspace.

The default case (1) (where no input parameter is given, and an "int" is
returned to userspace) encompasses more than 90% of the cases, but there
are two other exceptions. Here is a list of exceptions:

* Protocol RAW:
   * cmd = SIOCGETVIFCNT:
     * input and output = struct sioc_vif_req
   * cmd = SIOCGETSGCNT
     * input and output = struct sioc_sg_req
   * Explanation: for the SIOCGETVIFCNT case, userspace passes the input
     argument, which is struct sioc_vif_req. Then the callback populates
     the struct, which is copied back to userspace.

* Protocol RAW6:
   * cmd = SIOCGETMIFCNT_IN6
     * input and output = struct sioc_mif_req6
   * cmd = SIOCGETSGCNT_IN6
     * input and output = struct sioc_sg_req6

* Protocol PHONET:
  * cmd == SIOCPNADDRESOURCE | SIOCPNDELRESOURCE
     * input int (4 bytes)
  * Nothing is copied back to userspace.

For the exception cases, functions sock_sk_ioctl_inout() will
copy the userspace input, and copy it back to kernel space.

The wrapper that prepare the buffer and put the buffer back to user is
sk_ioctl(), so, instead of calling sk->sk_prot->ioctl(), the callee now
calls sk_ioctl(), which will handle all cases.

Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20230609152800.830401-1-leitao@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2 files changed, 5 insertions, 6 deletions

diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h
index a88e070b431d..91ebf0a3f499 100644
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -272,7 +272,7 @@ int l2tp_nl_register_ops(enum l2tp_pwtype pw_type, const struct l2tp_nl_cmd_ops
 void l2tp_nl_unregister_ops(enum l2tp_pwtype pw_type);
 
 /* IOCTL helper for IP encap modules. */
-int l2tp_ioctl(struct sock *sk, int cmd, unsigned long arg);
+int l2tp_ioctl(struct sock *sk, int cmd, int *karg);
 
 /* Extract the tunnel structure from a socket's sk_user_data pointer,
  * validating the tunnel magic feather.
diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c
index 41a74fc84ca1..2b795c1064f5 100644
--- a/net/l2tp/l2tp_ip.c
+++ b/net/l2tp/l2tp_ip.c
@@ -562,19 +562,18 @@ out:
 	return err ? err : copied;
 }
 
-int l2tp_ioctl(struct sock *sk, int cmd, unsigned long arg)
+int l2tp_ioctl(struct sock *sk, int cmd, int *karg)
 {
 	struct sk_buff *skb;
-	int amount;
 
 	switch (cmd) {
 	case SIOCOUTQ:
-		amount = sk_wmem_alloc_get(sk);
+		*karg = sk_wmem_alloc_get(sk);
 		break;
 	case SIOCINQ:
 		spin_lock_bh(&sk->sk_receive_queue.lock);
 		skb = skb_peek(&sk->sk_receive_queue);
-		amount = skb ? skb->len : 0;
+		*karg = skb ? skb->len : 0;
 		spin_unlock_bh(&sk->sk_receive_queue.lock);
 		break;
 
@@ -582,7 +581,7 @@ int l2tp_ioctl(struct sock *sk, int cmd, unsigned long arg)
 		return -ENOIOCTLCMD;
 	}
 
-	return put_user(amount, (int __user *)arg);
+	return 0;
 }
 EXPORT_SYMBOL_GPL(l2tp_ioctl);