Allow group access on PGDATA

Allow the cluster to be optionally init'd with read access for the
group.

This means a relatively non-privileged user can perform a backup of the
cluster without requiring write privileges, which enhances security.

The mode of PGDATA is used to determine whether group permissions are
enabled for directory and file creates.  This method was chosen as it's
simple and works well for the various utilities that write into PGDATA.

Changing the mode of PGDATA manually will not automatically change the
mode of all the files contained therein.  If the user would like to
enable group access on an existing cluster then changing the mode of all
the existing files will be required.  Note that pg_upgrade will
automatically change the mode of all migrated files if the new cluster
is init'd with the -g option.

Tests are included for the backend and all the utilities which operate
on the PG data directory to ensure that the correct mode is set based on
the data directory permissions.

Author: David Steele <david@pgmasters.net>
Reviewed-By: Michael Paquier, with discussion amongst many others.
Discussion: https://postgr.es/m/ad346fe6-b23e-59f1-ecb7-0e08390ad629%40pgmasters.net

1 files changed, 18 insertions, 8 deletions

diff --git a/src/bin/pg_basebackup/pg_basebackup.c b/src/bin/pg_basebackup/pg_basebackup.c
index 32b41e313cc..58f780c0691 100644
--- a/src/bin/pg_basebackup/pg_basebackup.c
+++ b/src/bin/pg_basebackup/pg_basebackup.c
@@ -2470,14 +2470,6 @@ main(int argc, char **argv)
 	}
 #endif
 
-	/*
-	 * Verify that the target directory exists, or create it. For plaintext
-	 * backups, always require the directory. For tar backups, require it
-	 * unless we are writing to stdout.
-	 */
-	if (format == 'p' || strcmp(basedir, "-") != 0)
-		verify_dir_is_empty_or_create(basedir, &made_new_pgdata, &found_existing_pgdata);
-
 	/* connection in replication mode to server */
 	conn = GetConnection();
 	if (!conn)
@@ -2486,6 +2478,24 @@ main(int argc, char **argv)
 		exit(1);
 	}
 
+	/*
+	 * Set umask so that directories/files are created with the same
+	 * permissions as directories/files in the source data directory.
+	 *
+	 * pg_mode_mask is set to owner-only by default and then updated in
+	 * GetConnection() where we get the mode from the server-side with
+	 * RetrieveDataDirCreatePerm() and then call SetDataDirectoryCreatePerm().
+	 */
+	umask(pg_mode_mask);
+
+	/*
+	 * Verify that the target directory exists, or create it. For plaintext
+	 * backups, always require the directory. For tar backups, require it
+	 * unless we are writing to stdout.
+	 */
+	if (format == 'p' || strcmp(basedir, "-") != 0)
+		verify_dir_is_empty_or_create(basedir, &made_new_pgdata, &found_existing_pgdata);
+
 	/* determine remote server's xlog segment size */
 	if (!RetrieveWalSegSize(conn))
 		disconnect_and_exit(1);