Add function fd_open_atomic() which uses O_CREAT|O_EXCL to return a guaranteed indication of creation of a new file.

1 files changed, 107 insertions, 4 deletions

diff --git a/source3/smbd/open.c b/source3/smbd/open.c
index 473fd9769c..6f1af4b4c4 100644
--- a/source3/smbd/open.c
+++ b/source3/smbd/open.c
@@ -534,6 +534,107 @@ NTSTATUS change_dir_owner_to_parent(connection_struct *conn,
 }
 
 /****************************************************************************
+ Open a file - returning a guaranteed ATOMIC indication of if the
+ file was created or not.
+****************************************************************************/
+
+static NTSTATUS fd_open_atomic(struct connection_struct *conn,
+			files_struct *fsp,
+			int flags,
+			mode_t mode,
+			bool *file_created)
+{
+	NTSTATUS status = NT_STATUS_UNSUCCESSFUL;
+	bool file_existed = VALID_STAT(fsp->fsp_name->st);
+
+	*file_created = false;
+
+	if (!(flags & O_CREAT)) {
+		/*
+		 * We're not creating the file, just pass through.
+		 */
+		return fd_open(conn, fsp, flags, mode);
+	}
+
+	if (flags & O_EXCL) {
+		/*
+		 * Fail if already exists, just pass through.
+		 */
+		status = fd_open(conn, fsp, flags, mode);
+		if (NT_STATUS_IS_OK(status)) {
+			/*
+			 * Here we've opened with O_CREAT|O_EXCL
+			 * and got success. We *know* we created
+			 * this file.
+			 */
+			*file_created = true;
+		}
+		return status;
+	}
+
+	/*
+	 * Now it gets tricky. We have O_CREAT, but not O_EXCL.
+	 * To know absolutely if we created the file or not,
+	 * we can never call O_CREAT without O_EXCL. So if
+	 * we think the file existed, try without O_CREAT|O_EXCL.
+	 * If we think the file didn't exist, try with
+	 * O_CREAT|O_EXCL. Keep bouncing between these two
+	 * requests until either the file is created, or
+	 * opened. Either way, we keep going until we get
+	 * a returnable result (error, or open/create).
+	 */
+
+	while(1) {
+		int curr_flags = flags;
+
+		if (file_existed) {
+			/* Just try open, do not create. */
+			curr_flags &= ~(O_CREAT);
+			status = fd_open(conn, fsp, curr_flags, mode);
+			if (NT_STATUS_EQUAL(status,
+					NT_STATUS_OBJECT_NAME_NOT_FOUND)) {
+				/*
+				 * Someone deleted it in the meantime.
+				 * Retry with O_EXCL.
+				 */
+				file_existed = false;
+				DEBUG(10,("fd_open_atomic: file %s existed. "
+					"Retry.\n",
+					smb_fname_str_dbg(fsp->fsp_name)));
+					continue;
+			}
+		} else {
+			/* Try create exclusively, fail if it exists. */
+			curr_flags |= O_EXCL;
+			status = fd_open(conn, fsp, curr_flags, mode);
+			if (NT_STATUS_EQUAL(status,
+					NT_STATUS_OBJECT_NAME_COLLISION)) {
+				/*
+				 * Someone created it in the meantime.
+				 * Retry without O_CREAT.
+				 */
+				file_existed = true;
+				DEBUG(10,("fd_open_atomic: file %s "
+					"did not exist. Retry.\n",
+					smb_fname_str_dbg(fsp->fsp_name)));
+				continue;
+			}
+			if (NT_STATUS_IS_OK(status)) {
+				/*
+				 * Here we've opened with O_CREAT|O_EXCL
+				 * and got success. We *know* we created
+				 * this file.
+				 */
+				*file_created = true;
+			}
+		}
+		/* Create is done, or failed. */
+		break;
+	}
+	return status;
+}
+
+/****************************************************************************
  Open a file.
 ****************************************************************************/
 
@@ -544,7 +645,8 @@ static NTSTATUS open_file(files_struct *fsp,
 			  int flags,
 			  mode_t unx_mode,
 			  uint32 access_mask, /* client requested access mask. */
-			  uint32 open_access_mask) /* what we're actually using in the open. */
+			  uint32 open_access_mask, /* what we're actually using in the open. */
+			  bool *p_file_created)
 {
 	struct smb_filename *smb_fname = fsp->fsp_name;
 	NTSTATUS status = NT_STATUS_OK;
@@ -670,7 +772,8 @@ static NTSTATUS open_file(files_struct *fsp,
 		}
 
 		/* Actually do the open */
-		status = fd_open(conn, fsp, local_flags, unx_mode);
+		status = fd_open_atomic(conn, fsp, local_flags,
+				unx_mode, p_file_created);
 		if (!NT_STATUS_IS_OK(status)) {
 			DEBUG(3,("Error opening file %s (%s) (local_flags=%d) "
 				 "(flags=%d)\n", smb_fname_str_dbg(smb_fname),
@@ -690,7 +793,7 @@ static NTSTATUS open_file(files_struct *fsp,
 			return status;
 		}
 
-		if ((local_flags & O_CREAT) && !file_existed) {
+		if (*p_file_created) {
 			/* We created this file. */
 
 			bool need_re_stat = false;
@@ -2236,7 +2339,7 @@ static NTSTATUS open_file_ntcreate(connection_struct *conn,
 
 	fsp_open = open_file(fsp, conn, req, parent_dir,
 			     flags|flags2, unx_mode, access_mask,
-			     open_access_mask);
+			     open_access_mask, &new_file_created);
 
 	if (!NT_STATUS_IS_OK(fsp_open)) {
 		if (NT_STATUS_EQUAL(fsp_open, NT_STATUS_RETRY)) {