[PATCH net-next 1/2] smc: convert to getsockopt_iter

[Breno Leitao <leitao@debian.org>]

Convert SMC socket's getsockopt implementation to use the new
getsockopt_iter callback with sockopt_t.

Key changes:
- Replace (char __user *optval, int __user *optlen) with sockopt_t *opt
- Use opt->optlen for buffer length (input) and returned size (output)
- Use copy_to_iter() instead of put_user()/copy_to_user()
- Add linux/uio.h for copy_to_iter()

SMC is a proxy socket: only the SOL_SMC level is handled locally, while
all other levels are forwarded to the underlying CLC (TCP) socket. That
socket's getsockopt() still operates on __user buffers, so the
pass-through is limited to user-backed iters: optval is reconstructed
from iter_out, the original optlen pointer (preserved in sockopt_t) is
forwarded, and the length reported by the clcsock is mirrored back into
opt->optlen so the core writes the correct value to userspace.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 net/smc/af_smc.c   | 41 +++++++++++++++++++++++++++++------------
 net/smc/smc.h      |  2 +-
 net/smc/smc_inet.c |  4 ++--
 3 files changed, 32 insertions(+), 15 deletions(-)

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index b5db69073e20..064d752388d2 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -27,6 +27,7 @@
 #include <linux/rcupdate_wait.h>
 #include <linux/ctype.h>
 #include <linux/splice.h>
+#include <linux/uio.h>
 
 #include <net/sock.h>
 #include <net/inet_common.h>
@@ -3017,17 +3018,14 @@ int smc_shutdown(struct socket *sock, int how)
 }
 
 static int __smc_getsockopt(struct socket *sock, int level, int optname,
-			    char __user *optval, int __user *optlen)
+			    sockopt_t *opt)
 {
 	struct smc_sock *smc;
 	int val, len;
 
 	smc = smc_sk(sock->sk);
 
-	if (get_user(len, optlen))
-		return -EFAULT;
-
-	len = min_t(int, len, sizeof(int));
+	len = min_t(int, opt->optlen, sizeof(int));
 
 	if (len < 0)
 		return -EINVAL;
@@ -3040,9 +3038,8 @@ static int __smc_getsockopt(struct socket *sock, int level, int optname,
 		return -EOPNOTSUPP;
 	}
 
-	if (put_user(len, optlen))
-		return -EFAULT;
-	if (copy_to_user(optval, &val, len))
+	opt->optlen = len;
+	if (copy_to_iter(&val, len, &opt->iter_out) != len)
 		return -EFAULT;
 
 	return 0;
@@ -3168,13 +3165,26 @@ int smc_setsockopt(struct socket *sock, int level, int optname,
 }
 
 int smc_getsockopt(struct socket *sock, int level, int optname,
-		   char __user *optval, int __user *optlen)
+		   sockopt_t *opt)
 {
 	struct smc_sock *smc;
 	int rc;
 
 	if (level == SOL_SMC)
-		return __smc_getsockopt(sock, level, optname, optval, optlen);
+		return __smc_getsockopt(sock, level, optname, opt);
+
+	/* Other levels apply to the CLC socket, whose getsockopt() still
+	 * operates on __user buffers. Reconstruct the userspace pointers and
+	 * forward the call; kernel-backed callers (e.g. io_uring) are not
+	 * supported for this pass-through.
+	 *
+	 * TODO: this pass-through is limited to user-backed iters because the
+	 * underlying protocols (TCP/IP) have not been converted to
+	 * getsockopt_iter() yet. Once they are, forward the sockopt_t directly
+	 * and drop this restriction so all iov_iter types are supported.
+	 */
+	if (!iter_is_ubuf(&opt->iter_out) || !opt->optlen_user)
+		return -EOPNOTSUPP;
 
 	smc = smc_sk(sock->sk);
 	mutex_lock(&smc->clcsock_release_lock);
@@ -3188,8 +3198,15 @@ int smc_getsockopt(struct socket *sock, int level, int optname,
 		return -EOPNOTSUPP;
 	}
 	rc = smc->clcsock->ops->getsockopt(smc->clcsock, level, optname,
-					   optval, optlen);
+					   opt->iter_out.ubuf, opt->optlen_user);
 	mutex_unlock(&smc->clcsock_release_lock);
+
+	/* The clcsock wrote the resulting length to the user optlen pointer;
+	 * mirror it into opt->optlen so the core writes the same value back.
+	 */
+	if (get_user(opt->optlen, opt->optlen_user))
+		return -EFAULT;
+
 	return rc;
 }
 
@@ -3341,7 +3358,7 @@ static const struct proto_ops smc_sock_ops = {
 	.listen		= smc_listen,
 	.shutdown	= smc_shutdown,
 	.setsockopt	= smc_setsockopt,
-	.getsockopt	= smc_getsockopt,
+	.getsockopt_iter = smc_getsockopt,
 	.sendmsg	= smc_sendmsg,
 	.recvmsg	= smc_recvmsg,
 	.mmap		= sock_no_mmap,
diff --git a/net/smc/smc.h b/net/smc/smc.h
index 52145df83f6e..e62549067b67 100644
--- a/net/smc/smc.h
+++ b/net/smc/smc.h
@@ -59,7 +59,7 @@ int smc_shutdown(struct socket *sock, int how);
 int smc_setsockopt(struct socket *sock, int level, int optname,
 		   sockptr_t optval, unsigned int optlen);
 int smc_getsockopt(struct socket *sock, int level, int optname,
-		   char __user *optval, int __user *optlen);
+		   sockopt_t *opt);
 int smc_sendmsg(struct socket *sock, struct msghdr *msg, size_t len);
 int smc_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
 		int flags);
diff --git a/net/smc/smc_inet.c b/net/smc/smc_inet.c
index a94084b4a498..419240fedbc3 100644
--- a/net/smc/smc_inet.c
+++ b/net/smc/smc_inet.c
@@ -44,7 +44,7 @@ static const struct proto_ops smc_inet_stream_ops = {
 	.listen		= smc_listen,
 	.shutdown	= smc_shutdown,
 	.setsockopt	= smc_setsockopt,
-	.getsockopt	= smc_getsockopt,
+	.getsockopt_iter = smc_getsockopt,
 	.sendmsg	= smc_sendmsg,
 	.recvmsg	= smc_recvmsg,
 	.mmap		= sock_no_mmap,
@@ -91,7 +91,7 @@ static const struct proto_ops smc_inet6_stream_ops = {
 	.listen		= smc_listen,
 	.shutdown	= smc_shutdown,
 	.setsockopt	= smc_setsockopt,
-	.getsockopt	= smc_getsockopt,
+	.getsockopt_iter = smc_getsockopt,
 	.sendmsg	= smc_sendmsg,
 	.recvmsg	= smc_recvmsg,
 	.mmap		= sock_no_mmap,

-- 
2.53.0-Meta