[PATCH 3/7] cifs: Add support for creating native Windows sockets

[Pali Rohár]

Native Windows sockets created by WinSock on Windows 10 April 2018 Update
(version 1803) or Windows Server 2019 (version 1809) or later versions is
reparse point with IO_REPARSE_TAG_AF_UNIX tag, with empty reparse point
data buffer and without any EAs.

Create AF_UNIX sockets in this native format when -o reparse=native or
-o reparse=native+<something> mount option is used.

This change makes AF_UNIX sockets created by Linux CIFS client compatible
with AF_UNIX sockets created by Windows applications on NTFS volumes.

Signed-off-by: Pali Rohár <pali@xxxxxxxxxx>
---
 fs/smb/client/cifsglob.h |  6 +++---
 fs/smb/client/reparse.c  | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/fs/smb/client/cifsglob.h b/fs/smb/client/cifsglob.h
index 7632d2ba5390..570b22d02f7e 100644
--- a/fs/smb/client/cifsglob.h
+++ b/fs/smb/client/cifsglob.h
@@ -155,9 +155,9 @@ enum securityEnum {
 
 enum cifs_reparse_type {
 	CIFS_REPARSE_TYPE_NONE, /* disable creating new reparse points */
-	CIFS_REPARSE_TYPE_NATIVE, /* native symlinks only */
-	CIFS_REPARSE_TYPE_NATIVE_NFS, /* native for symlinks, nfs for others */
-	CIFS_REPARSE_TYPE_NATIVE_WSL, /* native for symlinks, wsl for others */
+	CIFS_REPARSE_TYPE_NATIVE, /* native symlinks and sockets only, no support for others */
+	CIFS_REPARSE_TYPE_NATIVE_NFS, /* native for symlinks/sockets, nfs for fifos/block/char */
+	CIFS_REPARSE_TYPE_NATIVE_WSL, /* native for symlinks/sockets, wsl for fifos/block/char */
 	CIFS_REPARSE_TYPE_NFS, /* nfs for everything */
 	CIFS_REPARSE_TYPE_WSL, /* wsl for everything */
 	CIFS_REPARSE_TYPE_DEFAULT = CIFS_REPARSE_TYPE_NATIVE_NFS,
diff --git a/fs/smb/client/reparse.c b/fs/smb/client/reparse.c
index 38fe0a710c65..f1488f870320 100644
--- a/fs/smb/client/reparse.c
+++ b/fs/smb/client/reparse.c
@@ -379,6 +379,35 @@ static int detect_directory_symlink_target(struct cifs_sb_info *cifs_sb,
 	return 0;
 }
 
+static int create_native_socket(const unsigned int xid, struct inode *inode,
+				struct dentry *dentry, struct cifs_tcon *tcon,
+				const char *full_path)
+{
+	struct cifs_open_info_data data = {
+		.reparse_point = true,
+		.reparse = { .tag = IO_REPARSE_TAG_AF_UNIX, },
+	};
+	struct reparse_data_buffer buf = {
+		.ReparseTag = cpu_to_le32(IO_REPARSE_TAG_AF_UNIX),
+		.ReparseDataLength = 0,
+	};
+	struct kvec iov = {
+		.iov_base = &buf,
+		.iov_len = sizeof(buf),
+	};
+	struct inode *new;
+	int rc;
+
+	new = smb2_get_reparse_inode(&data, inode->i_sb, xid,
+				     tcon, full_path, false, &iov, NULL);
+	if (!IS_ERR(new))
+		d_instantiate(dentry, new);
+	else
+		rc = PTR_ERR(new);
+	cifs_free_open_info(&data);
+	return rc;
+}
+
 static int nfs_set_reparse_buf(struct reparse_posix_data *buf,
 			       mode_t mode, dev_t dev,
 			       struct kvec *iov)
@@ -602,6 +631,13 @@ int smb2_mknod_reparse(unsigned int xid, struct inode *inode,
 {
 	struct smb3_fs_context *ctx = CIFS_SB(inode->i_sb)->ctx;
 
+	if (S_ISSOCK(mode) && (
+	     ctx->reparse_type == CIFS_REPARSE_TYPE_NATIVE ||
+	     ctx->reparse_type == CIFS_REPARSE_TYPE_NATIVE_NFS ||
+	     ctx->reparse_type == CIFS_REPARSE_TYPE_NATIVE_WSL)) {
+		return create_native_socket(xid, inode, dentry, tcon, full_path);
+	}
+
 	switch (ctx->reparse_type) {
 	case CIFS_REPARSE_TYPE_NATIVE_NFS:
 	case CIFS_REPARSE_TYPE_NFS:
-- 
2.20.1