[RFC PATCH 3/4] ksmbd: complete TCP frames before reporting send success

[Huiwen He <huiwen.he@linux.dev>]

From: Huiwen He <hehuiwen@kylinos.cn>

A positive kernel_sendmsg() return may cover only part of an SMB frame.
Reporting success lets the next response follow an incomplete frame.

Retry short sends with the same iterator while holding srv_mutex.
On zero progress or error, shut down the socket before releasing the
lock so no later response can follow an incomplete frame.

Signed-off-by: Huiwen He <hehuiwen@kylinos.cn>
---
 fs/smb/server/transport_tcp.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/fs/smb/server/transport_tcp.c b/fs/smb/server/transport_tcp.c
index 5a2aad35739d..1183bb75aa24 100644
--- a/fs/smb/server/transport_tcp.c
+++ b/fs/smb/server/transport_tcp.c
@@ -437,9 +437,22 @@ static int ksmbd_tcp_writev(struct ksmbd_transport *t,
 	struct msghdr smb_msg = {
 		.msg_flags = MSG_NOSIGNAL | tx->msg_flags,
 	};
+	struct socket *sock = TCP_TRANS(t)->sock;
+	int ret;
+
+	iov_iter_kvec(&smb_msg.msg_iter, ITER_SOURCE, tx->iov,
+		      tx->iov_cnt, tx->size);
+	/* The caller holds srv_mutex across the entire frame. */
+	while (iov_iter_count(&smb_msg.msg_iter)) {
+		ret = sock_sendmsg(sock, &smb_msg);
+		if (ret <= 0) {
+			/* Never append another SMB frame to an incomplete one. */
+			kernel_sock_shutdown(sock, SHUT_RDWR);
+			return ret ?: -EIO;
+		}
+	}
 
-	return kernel_sendmsg(TCP_TRANS(t)->sock, &smb_msg, tx->iov,
-			      tx->iov_cnt, tx->size);
+	return tx->size;
 }
 
 static void ksmbd_tcp_disconnect(struct ksmbd_transport *t)
-- 
2.43.0