ksmbd: allow a filename to contain colons on SMB3.1.1 posix extensions

If the client sends SMB2_CREATE_POSIX_CONTEXT to ksmbd, allow the filename
to contain a colon (':'). This requires disabling the support for Alternate
Data Streams (ADS), which are denoted by a colon-separated suffix to the
filename on Windows. This should not be an issue, since this concept is not
known to POSIX anyway and the client has to explicitly request a POSIX
context to get this behavior.

Link: https://lore.kernel.org/all/[e-mail]/
Signed-off-by: Philipp Kerling <[e-mail]>
Acked-by: Namjae Jeon <[e-mail]>
Signed-off-by: Steve French <[e-mail]>

fs/smb/server/smb2pdu.c

···
 		}
 
 		ksmbd_debug(SMB, "converted name = %s\n", name);
-		if (strchr(name, ':')) {
-			if (!test_share_config_flag(work->tcon->share_conf,
-						    KSMBD_SHARE_FLAG_STREAMS)) {
-				rc = -EBADF;
-				goto err_out2;
-			}
-			rc = parse_stream_name(name, &stream_name, &s_type);
-			if (rc < 0)
-				goto err_out2;
-		}
 
 		if (posix_ctxt == false) {
+			if (strchr(name, ':')) {
+				if (!test_share_config_flag(work->tcon->share_conf,
+							KSMBD_SHARE_FLAG_STREAMS)) {
+					rc = -EBADF;
+					goto err_out2;
+				}
+				rc = parse_stream_name(name, &stream_name, &s_type);
+				if (rc < 0)
+					goto err_out2;
+			}
+
 			rc = ksmbd_validate_filename(name);
 			if (rc < 0)
 				goto err_out2;
···
 
 	fp->attrib_only = !(req->DesiredAccess & ~(FILE_READ_ATTRIBUTES_LE |
 			FILE_WRITE_ATTRIBUTES_LE | FILE_SYNCHRONIZE_LE));
+
+	fp->is_posix_ctxt = posix_ctxt;
 
 	/* fp should be searchable through ksmbd_inode.m_fp_list
 	 * after daccess, saccess, attrib_only, and stream are
···
 	if (IS_ERR(new_name))
 		return PTR_ERR(new_name);
 
-	if (strchr(new_name, ':')) {
+	if (fp->is_posix_ctxt == false && strchr(new_name, ':')) {
 		int s_type;
 		char *xattr_stream_name, *stream_name = NULL;
 		size_t xattr_stream_size;

fs/smb/server/vfs_cache.h

···
 	bool				is_durable;
 	bool				is_persistent;
 	bool				is_resilient;
+
+	bool                            is_posix_ctxt;
 };
 
 static inline void set_ctx_actor(struct dir_context *ctx,