Re: [RFC PATCH 0/4] net/io_uring: pass a kernel pointer via optlen_t to proto[_ops].getsockopt()

[Stefan Metzmacher <metze@samba.org>]

Am 01.04.25 um 10:19 schrieb Stefan Metzmacher:
> Am 31.03.25 um 23:04 schrieb Stanislav Fomichev:
>> On 03/31, Stefan Metzmacher wrote:
>>> The motivation for this is to remove the SOL_SOCKET limitation
>>> from io_uring_cmd_getsockopt().
>>>
>>> The reason for this limitation is that io_uring_cmd_getsockopt()
>>> passes a kernel pointer as optlen to do_sock_getsockopt()
>>> and can't reach the ops->getsockopt() path.
>>>
>>> The first idea would be to change the optval and optlen arguments
>>> to the protocol specific hooks also to sockptr_t, as that
>>> is already used for setsockopt() and also by do_sock_getsockopt()
>>> sk_getsockopt() and BPF_CGROUP_RUN_PROG_GETSOCKOPT().
>>>
>>> But as Linus don't like 'sockptr_t' I used a different approach.
>>>
>>> @Linus, would that optlen_t approach fit better for you?
>>
>> [..]
>>
>>> Instead of passing the optlen as user or kernel pointer,
>>> we only ever pass a kernel pointer and do the
>>> translation from/to userspace in do_sock_getsockopt().
>>
>> At this point why not just fully embrace iov_iter? You have the size
>> now + the user (or kernel) pointer. Might as well do
>> s/sockptr_t/iov_iter/ conversion?
> 
> I think that would only be possible if we introduce
> proto[_ops].getsockopt_iter() and then convert the implementations
> step by step. Doing it all in one go has a lot of potential to break
> the uapi. I could try to convert things like socket, ip and tcp myself, but
> the rest needs to be converted by the maintainer of the specific protocol,
> as it needs to be tested. As there are crazy things happening in the existing
> implementations, e.g. some getsockopt() implementations use optval as in and out
> buffer.
> 
> I first tried to convert both optval and optlen of getsockopt to sockptr_t,
> and that showed that touching the optval part starts to get complex very soon,
> see https://git.samba.org/?p=metze/linux/wip.git;a=commitdiff;h=141912166473bf8843ec6ace76dc9c6945adafd1
> (note it didn't converted everything, I gave up after hitting
> sctp_getsockopt_peer_addrs and sctp_getsockopt_local_addrs.
> sctp_getsockopt_context, sctp_getsockopt_maxseg, sctp_getsockopt_associnfo and maybe
> more are the ones also doing both copy_from_user and copy_to_user on optval)
> 
> I come also across one implementation that returned -ERANGE because *optlen was
> too short and put the required length into *optlen, which means the returned
> *optlen is larger than the optval buffer given from userspace.
> 
> Because of all these strange things I tried to do a minimal change
> in order to get rid of the io_uring limitation and only converted
> optlen and leave optval as is.
> 
> In order to have a patchset that has a low risk to cause regressions.
> 
> But as alternative introducing a prototype like this:
> 
>          int (*getsockopt_iter)(struct socket *sock, int level, int optname,
>                                 struct iov_iter *optval_iter);
> 
> That returns a non-negative value which can be placed into *optlen
> or negative value as error and *optlen will not be changed on error.
> optval_iter will get direction ITER_DEST, so it can only be written to.
> 
> Implementations could then opt in for the new interface and
> allow do_sock_getsockopt() work also for the io_uring case,
> while all others would still get -EOPNOTSUPP.
> 
> So what should be the way to go?

Ok, I've added the infrastructure for getsockopt_iter, see below,
but the first part I wanted to convert was
tcp_ao_copy_mkts_to_user() and that also reads from userspace before
writing.

So we could go with the optlen_t approach, or we need
logic for ITER_BOTH or pass two iov_iters one with ITER_SRC and one
with ITER_DEST...

So who wants to decide?

Thanks!
metze
---
  include/linux/net.h |  4 +++
  include/net/sock.h  | 64 +++++++++++++++++++++++++++++++++++++++++++++
  net/core/sock.c     | 12 +++++++--
  net/socket.c        | 12 +++++++--
  4 files changed, 88 insertions(+), 4 deletions(-)

diff --git a/include/linux/net.h b/include/linux/net.h
index 0ff950eecc6b..ceb9f9ed84b9 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -194,6 +194,10 @@ struct proto_ops {
  				      unsigned int optlen);
  	int		(*getsockopt)(struct socket *sock, int level,
  				      int optname, char __user *optval, int __user *optlen);
+	int		(*getsockopt_iter)(struct socket *sock,
+					   int level,
+					   int optname,
+					   struct iov_iter *optval_iter);
  	void		(*show_fdinfo)(struct seq_file *m, struct socket *sock);
  	int		(*sendmsg)   (struct socket *sock, struct msghdr *m,
  				      size_t total_len);
diff --git a/include/net/sock.h b/include/net/sock.h
index 8daf1b3b12c6..e741b219056e 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1249,6 +1249,11 @@ struct proto {
  	int			(*getsockopt)(struct sock *sk, int level,
  					int optname, char __user *optval,
  					int __user *option);
+	int			(*getsockopt_iter)(struct sock *sk,
+						   int level,
+						   int optname,
+						   struct iov_iter *optval_iter);
+
  	void			(*keepalive)(struct sock *sk, int valbool);
  #ifdef CONFIG_COMPAT
  	int			(*compat_ioctl)(struct sock *sk,
@@ -1781,6 +1786,65 @@ int do_sock_setsockopt(struct socket *sock, bool compat, int level,
  int do_sock_getsockopt(struct socket *sock, bool compat, int level,
  		       int optname, sockptr_t optval, sockptr_t optlen);

+#define __generic_wrap_getsockopt_iter(__s, __level,				\
+				       __optname, __optval, __optlen, 		\
+				       __getsockopt_iter) 			\
+do {										\
+	struct iov_iter optval_iter;						\
+	struct kvec optval_kvec;						\
+	int len;								\
+	int err;								\
+										\
+	if (unlikely(__getsockopt_iter == NULL))				\
+		return -EOPNOTSUPP;						\
+										\
+	if (copy_from_sockptr(&len, __optlen, sizeof(len)))			\
+		return -EFAULT;							\
+										\
+	if (len < 0)								\
+		return -EINVAL;							\
+										\
+	if (__optval.is_kernel) {						\
+		if (__optval.kernel == NULL && len != 0)			\
+			return -EFAULT;						\
+										\
+		optval_kvec = (struct kvec) {					\
+			.iov_base = __optval.kernel,				\
+			.iov_len = len,						\
+		};								\
+										\
+		iov_iter_kvec(&optval_iter, ITER_DEST,				\
+			      &optval_kvec, 1, optval_kvec.iov_len);		\
+	} else {								\
+		if (import_ubuf(ITER_DEST, __optval.user, len, &optval_iter))	\
+			return -EFAULT;						\
+	}									\
+										\
+	err = getsockopt_iter(__s, __level, __optname, &optval_iter);		\
+	if (unlikely(err < 0))							\
+		return err;							\
+										\
+	len = err;								\
+	if (copy_to_sockptr(__optlen, &len, sizeof(len)))			\
+		return -EFAULT;							\
+										\
+	return 0;								\
+} while (0)
+
+static __always_inline
+int sk_wrap_getsockopt_iter(struct sock *sk, int level, int optname, sockptr_t optval, sockptr_t optlen,
+	    int (*getsockopt_iter)(struct sock *sk, int level, int optname, struct iov_iter *optval_iter))
+{
+	__generic_wrap_getsockopt_iter(sk, level, optname, optval, optlen, getsockopt_iter);
+}
+
+static __always_inline
+int sock_wrap_getsockopt_iter(struct socket *sock, int level, int optname, sockptr_t optval, sockptr_t optlen,
+	    int (*getsockopt_iter)(struct socket *sock, int level, int optname, struct iov_iter *optval_iter))
+{
+	__generic_wrap_getsockopt_iter(sock, level, optname, optval, optlen, getsockopt_iter);
+}
+
  int sk_getsockopt(struct sock *sk, int level, int optname,
  		  sockptr_t optval, sockptr_t optlen);
  int sock_gettstamp(struct socket *sock, void __user *userstamp,
diff --git a/net/core/sock.c b/net/core/sock.c
index 323892066def..61625060e724 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -3857,9 +3857,17 @@ int sock_common_getsockopt(struct socket *sock, int level, int optname,
  			   char __user *optval, int __user *optlen)
  {
  	struct sock *sk = sock->sk;
-
  	/* IPV6_ADDRFORM can change sk->sk_prot under us. */
-	return READ_ONCE(sk->sk_prot)->getsockopt(sk, level, optname, optval, optlen);
+	struct proto *prot = READ_ONCE(sk->sk_prot);
+
+	if (prot->getsockopt_iter) {
+		return sk_wrap_getsockopt_iter(sk, level, optname,
+					       USER_SOCKPTR(optval),
+					       USER_SOCKPTR(optlen),
+					       prot->getsockopt_iter);
+	}
+
+	return prot->getsockopt(sk, level, optname, optval, optlen);
  }
  EXPORT_SYMBOL(sock_common_getsockopt);

diff --git a/net/socket.c b/net/socket.c
index 9a0e720f0859..792cfd272611 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2335,6 +2335,7 @@ int do_sock_getsockopt(struct socket *sock, bool compat, int level,
  {
  	int max_optlen __maybe_unused = 0;
  	const struct proto_ops *ops;
+	const struct proto *prot;
  	int err;

  	err = security_socket_getsockopt(sock, level, optname);
@@ -2345,12 +2346,19 @@ int do_sock_getsockopt(struct socket *sock, bool compat, int level,
  		copy_from_sockptr(&max_optlen, optlen, sizeof(int));

  	ops = READ_ONCE(sock->ops);
+	prot = READ_ONCE(sock->sk->sk_prot);
  	if (level == SOL_SOCKET) {
  		err = sk_getsockopt(sock->sk, level, optname, optval, optlen);
-	} else if (unlikely(!ops->getsockopt)) {
+	} else if (ops->getsockopt_iter) {
+		err = sock_wrap_getsockopt_iter(sock, level, optname, optval, optlen,
+					        ops->getsockopt_iter);
+	} else if (ops->getsockopt == sock_common_getsockopt && prot->getsockopt_iter) {
+		err = sk_wrap_getsockopt_iter(sock->sk, level, optname, optval, optlen,
+					      prot->getsockopt_iter);
+	} else if (unlikely(!ops->getsockopt || optlen.is_kernel)) {
  		err = -EOPNOTSUPP;
  	} else {
-		if (WARN_ONCE(optval.is_kernel || optlen.is_kernel,
+		if (WARN_ONCE(optval.is_kernel,
  			      "Invalid argument type"))
  			return -EOPNOTSUPP;

-- 
2.34.1