[PATCH v2 3/3] smb/server: use MSG_EOR for async interim response

[ChenXiaoSong <chenxiaosong@chenxiaosong.com>]

From: ChenXiaoSong <chenxiaosong@kylinos.cn>

Two kernel_sendmsg() calls can still use the same TCP skb if the first skb
can take more data. This can happen when ksmbd sends two SMB2 responses
very close to each other.

Without MSG_EOR, TCP can append the next sendmsg data to the previous skb.
Then STATUS_PENDING and the later response can be put into the same TCP
skb. MSG_EOR marks the skb as end of record, so TCP will not collapse the
next sendmsg data into it.

Example:

  smbtorture //${server_ip}/export -U${username}%${password} smb2.compound_async.write_write

  Client request:

    Write Request Len:64 Off:0, File: compound_async_write_write; Write Request Len:64 Off:64

  Before this patch, server responses:

    Write Response, File: compound_async_write_write
    Write Response
      SMB2, STATUS_PENDING, Write Response, MessageId 7
      SMB2, Write Response, MessageId 7

  After this patch:

    Write Response, File: compound_async_write_write
    Write Response, Error: STATUS_PENDING
    Write Response

Signed-off-by: ChenXiaoSong <chenxiaosong@kylinos.cn>
---
 fs/smb/server/connection.c    | 9 +++++++++
 fs/smb/server/connection.h    | 2 ++
 fs/smb/server/smb2pdu.c       | 4 ++--
 fs/smb/server/transport_tcp.c | 2 +-
 4 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/fs/smb/server/connection.c b/fs/smb/server/connection.c
index d5b35087556e..89746284fd7b 100644
--- a/fs/smb/server/connection.c
+++ b/fs/smb/server/connection.c
@@ -392,6 +392,15 @@ int ksmbd_conn_write(struct ksmbd_work *work)
 	return __ksmbd_conn_write(work, &write);
 }
 
+int ksmbd_conn_write_eor(struct ksmbd_work *work)
+{
+	struct ksmbd_transport_write write = {
+		.msg_flags = MSG_EOR,
+	};
+
+	return __ksmbd_conn_write(work, &write);
+}
+
 int ksmbd_conn_rdma_read(struct ksmbd_conn *conn,
 			 void *buf, unsigned int buflen,
 			 struct smbdirect_buffer_descriptor_v1 *desc,
diff --git a/fs/smb/server/connection.h b/fs/smb/server/connection.h
index 62df151ca554..fa09d37d5745 100644
--- a/fs/smb/server/connection.h
+++ b/fs/smb/server/connection.h
@@ -138,6 +138,7 @@ struct ksmbd_transport_write {
 	int		size;
 	bool		need_invalidate_rkey;
 	unsigned int	remote_key;
+	int		msg_flags;
 };
 
 struct ksmbd_transport_ops {
@@ -182,6 +183,7 @@ int ksmbd_conn_wq_init(void);
 void ksmbd_conn_wq_destroy(void);
 bool ksmbd_conn_lookup_dialect(struct ksmbd_conn *c);
 int ksmbd_conn_write(struct ksmbd_work *work);
+int ksmbd_conn_write_eor(struct ksmbd_work *work);
 int ksmbd_conn_rdma_read(struct ksmbd_conn *conn,
 			 void *buf, unsigned int buflen,
 			 struct smbdirect_buffer_descriptor_v1 *desc,
diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index 35f8476bbb6d..d644134d50f0 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -867,7 +867,7 @@ static void smb2_send_interim_compound_prefix(struct ksmbd_work *work)
 	    work->conn->ops->set_sign_rsp)
 		work->conn->ops->set_sign_rsp(work);
 
-	err = ksmbd_conn_write(work);
+	err = ksmbd_conn_write_eor(work);
 	if (err)
 		ksmbd_debug(SMB, "failed to send compound interim prefix: %d\n",
 			    err);
@@ -908,7 +908,7 @@ void smb2_send_interim_resp(struct ksmbd_work *work, __le32 status)
 	smb2_set_err_rsp(in_work);
 	rsp_hdr->Status = status;
 
-	ksmbd_conn_write(in_work);
+	ksmbd_conn_write_eor(in_work);
 	ksmbd_free_work_struct(in_work);
 }
 
diff --git a/fs/smb/server/transport_tcp.c b/fs/smb/server/transport_tcp.c
index 448f24d44b6b..cf81585d6861 100644
--- a/fs/smb/server/transport_tcp.c
+++ b/fs/smb/server/transport_tcp.c
@@ -421,7 +421,7 @@ static int ksmbd_tcp_writev(struct ksmbd_transport *t,
 			    const struct ksmbd_transport_write *write)
 {
 	struct msghdr smb_msg = {
-		.msg_flags = MSG_NOSIGNAL,
+		.msg_flags = MSG_NOSIGNAL | write->msg_flags,
 	};
 
 	return kernel_sendmsg(TCP_TRANS(t)->sock, &smb_msg, write->iov,
-- 
2.54.0