[PATCH v1 1/2] vfs: Add new setgid_create_umask test

* [PATCH v1 1/2] vfs: Add new setgid_create_umask test
@ 2022-05-20 16:04 Yang Xu
  2022-05-20 16:04 ` [PATCH v1 2/2] vfs: Add new setgid_create_acl test Yang Xu
                   ` (2 more replies)
  0 siblings, 3 replies; 15+ messages in thread
From: Yang Xu @ 2022-05-20 16:04 UTC (permalink / raw)
  To: fstests; +Cc: Yang Xu

The current_umask() is stripped from the mode directly in the vfs if the
filesystem either doesn't support acls or the filesystem has been
mounted without posic acl support.

If the filesystem does support acls then current_umask() stripping is
deferred to posix_acl_create(). So when the filesystem calls
posix_acl_create() and there are no acls set or not supported then
current_umask() will be stripped.

This patch is also designed to test kernel patchset behaviour
"move S_ISGID stripping into the vfs"
https://patchwork.kernel.org/project/linux-fsdevel/list/?series=635692

Here we only use umask(S_IXGRP) to check whether inode strip
S_ISGID works correctly and check whether S_IXGRP mode exists.

Signed-off-by: Yang Xu <xuyang2018.jy@fujitsu.com>
---
 src/vfs/idmapped-mounts.c | 429 ++++++++++++++++++++++++++++++++++++++
 src/vfs/idmapped-mounts.h |   1 +
 src/vfs/utils.c           |  14 ++
 src/vfs/utils.h           |   1 +
 src/vfs/vfstest.c         | 205 +++++++++++++++++-
 tests/generic/691         |  40 ++++
 tests/generic/691.out     |   2 +
 7 files changed, 691 insertions(+), 1 deletion(-)
 create mode 100755 tests/generic/691
 create mode 100644 tests/generic/691.out

diff --git a/src/vfs/idmapped-mounts.c b/src/vfs/idmapped-mounts.c
index 63297d5f..72de52cc 100644
--- a/src/vfs/idmapped-mounts.c
+++ b/src/vfs/idmapped-mounts.c
@@ -7664,6 +7664,425 @@ out:
 	return fret;
 }
 
+static int setgid_create_umask_idmapped(const struct vfstest_info *info)
+{
+	int fret = -1;
+	int file1_fd = -EBADF, open_tree_fd = -EBADF;
+	struct mount_attr attr = {
+		.attr_set = MOUNT_ATTR_IDMAP,
+	};
+	pid_t pid;
+	int tmpfile_fd = -EBADF;
+	bool supported = false;
+	char path[PATH_MAX];
+	mode_t mode;
+
+	if (!caps_supported())
+		return 0;
+
+	if (fchmod(info->t_dir1_fd, S_IRUSR |
+			      S_IWUSR |
+			      S_IRGRP |
+			      S_IWGRP |
+			      S_IROTH |
+			      S_IWOTH |
+			      S_IXUSR |
+			      S_IXGRP |
+			      S_IXOTH |
+			      S_ISGID), 0) {
+		log_stderr("failure: fchmod");
+		goto out;
+	}
+
+	/* Verify that the sid bits got raised. */
+	if (!is_setgid(info->t_dir1_fd, "", AT_EMPTY_PATH)) {
+		log_stderr("failure: is_setgid");
+		goto out;
+	}
+
+	/* Changing mount properties on a detached mount. */
+	attr.userns_fd	= get_userns_fd(0, 10000, 10000);
+	if (attr.userns_fd < 0) {
+		log_stderr("failure: get_userns_fd");
+		goto out;
+	}
+
+	open_tree_fd = sys_open_tree(info->t_dir1_fd, "",
+				     AT_EMPTY_PATH |
+				     AT_NO_AUTOMOUNT |
+				     AT_SYMLINK_NOFOLLOW |
+				     OPEN_TREE_CLOEXEC |
+				     OPEN_TREE_CLONE);
+	if (open_tree_fd < 0) {
+		log_stderr("failure: sys_open_tree");
+		goto out;
+	}
+
+	if (sys_mount_setattr(open_tree_fd, "", AT_EMPTY_PATH, &attr, sizeof(attr))) {
+		log_stderr("failure: sys_mount_setattr");
+		goto out;
+	}
+
+	supported = openat_tmpfile_supported(open_tree_fd);
+
+	/* Only umask with S_IXGRP because inode strip S_ISGID will check mode
+	 * whether has group execute or search permission.
+	 */
+	umask(S_IXGRP);
+	mode = umask(S_IXGRP);
+	if (!(mode & S_IXGRP))
+		die("failure: umask");
+
+		pid = fork();
+	if (pid < 0) {
+		log_stderr("failure: fork");
+		goto out;
+	}
+	if (pid == 0) {
+		if (!switch_ids(10000, 11000))
+			die("failure: switch fsids");
+
+		/* create regular file via open() */
+		file1_fd = openat(open_tree_fd, FILE1, O_CREAT | O_EXCL | O_CLOEXEC, S_IXGRP | S_ISGID);
+		if (file1_fd < 0)
+			die("failure: create");
+
+		/* Neither in_group_p() nor capable_wrt_inode_uidgid() so setgid
+		 * bit needs to be stripped.
+		 */
+		if (is_setgid(open_tree_fd, FILE1, 0))
+			die("failure: is_setgid");
+
+		if (is_ixgrp(open_tree_fd, FILE1, 0))
+			die("failure: is_ixgrp");
+
+		/* create directory */
+		if (mkdirat(open_tree_fd, DIR1, 0000))
+			die("failure: create");
+
+		if (xfs_irix_sgid_inherit_enabled(info->t_fstype)) {
+			/* We're not in_group_p(). */
+			if (is_setgid(open_tree_fd, DIR1, 0))
+				die("failure: is_setgid");
+		} else {
+			/* Directories always inherit the setgid bit. */
+			if (!is_setgid(open_tree_fd, DIR1, 0))
+				die("failure: is_setgid");
+		}
+
+		if (is_ixgrp(open_tree_fd, DIR1, 0))
+			die("failure: is_ixgrp");
+
+		/* create a special file via mknodat() vfs_create */
+		if (mknodat(open_tree_fd, FILE2, S_IFREG | S_ISGID | S_IXGRP, 0))
+			die("failure: mknodat");
+
+		if (is_setgid(open_tree_fd, FILE2, 0))
+			die("failure: is_setgid");
+
+		if (is_ixgrp(open_tree_fd, FILE2, 0))
+			die("failure: is_ixgrp");
+
+		/* create a whiteout device via mknodat() vfs_mknod */
+		if (mknodat(open_tree_fd, CHRDEV1, S_IFCHR | S_ISGID | S_IXGRP, 0))
+			die("failure: mknodat");
+
+		if (is_setgid(open_tree_fd, CHRDEV1, 0))
+			die("failure: is_setgid");
+
+		if (is_ixgrp(open_tree_fd, CHRDEV1, 0))
+			die("failure: is_ixgrp");
+
+		/*
+		 * In setgid directories newly created files always inherit the
+		 * gid from the parent directory. Verify that the file is owned
+		 * by gid 10000, not by gid 11000.
+		 */
+		if (!expected_uid_gid(open_tree_fd, FILE1, 0, 10000, 10000))
+			die("failure: check ownership");
+
+		/*
+		 * In setgid directories newly created directories always
+		 * inherit the gid from the parent directory. Verify that the
+		 * directory is owned by gid 10000, not by gid 11000.
+		 */
+		if (!expected_uid_gid(open_tree_fd, DIR1, 0, 10000, 10000))
+			die("failure: check ownership");
+
+		if (!expected_uid_gid(open_tree_fd, FILE2, 0, 10000, 10000))
+			die("failure: check ownership");
+
+		if (!expected_uid_gid(open_tree_fd, CHRDEV1, 0, 10000, 10000))
+			die("failure: check ownership");
+
+		if (unlinkat(open_tree_fd, FILE1, 0))
+			die("failure: delete");
+
+		if (unlinkat(open_tree_fd, DIR1, AT_REMOVEDIR))
+			die("failure: delete");
+
+		if (unlinkat(open_tree_fd, FILE2, 0))
+			die("failure: delete");
+
+		if (unlinkat(open_tree_fd, CHRDEV1, 0))
+			die("failure: delete");
+
+		/* create tmpfile via filesystem tmpfile api */
+		if (supported) {
+			tmpfile_fd = openat(open_tree_fd, ".", O_TMPFILE | O_RDWR, S_IXGRP | S_ISGID);
+			if (tmpfile_fd < 0)
+				die("failure: create");
+			/* link the temporary file into the filesystem, making it permanent */
+			snprintf(path, PATH_MAX,  "/proc/self/fd/%d", tmpfile_fd);
+			if (linkat(AT_FDCWD, path, open_tree_fd, FILE3, AT_SYMLINK_FOLLOW))
+				die("failure: linkat");
+			if (close(tmpfile_fd))
+				die("failure: close");
+			if (is_setgid(open_tree_fd, FILE3, 0))
+				die("failure: is_setgid");
+			if (is_ixgrp(open_tree_fd, FILE3, 0))
+				die("failure: is_ixgrp");
+			if (!expected_uid_gid(open_tree_fd, FILE3, 0, 10000, 10000))
+				die("failure: check ownership");
+			if (unlinkat(open_tree_fd, FILE3, 0))
+				die("failure: delete");
+		}
+
+		exit(EXIT_SUCCESS);
+	}
+	if (wait_for_pid(pid))
+		goto out;
+
+	fret = 0;
+	log_debug("Ran test");
+out:
+	safe_close(attr.userns_fd);
+	safe_close(file1_fd);
+	safe_close(open_tree_fd);
+
+	return fret;
+}
+
+static int setgid_create_umask_idmapped_in_userns(const struct vfstest_info *info)
+{
+	int fret = -1;
+	int file1_fd = -EBADF, open_tree_fd = -EBADF;
+	struct mount_attr attr = {
+		.attr_set = MOUNT_ATTR_IDMAP,
+	};
+	pid_t pid;
+	int tmpfile_fd = -EBADF;
+	bool supported = false;
+	char path[PATH_MAX];
+	mode_t mode;
+
+	if (!caps_supported())
+		return 0;
+
+	if (fchmod(info->t_dir1_fd, S_IRUSR |
+			      S_IWUSR |
+			      S_IRGRP |
+			      S_IWGRP |
+			      S_IROTH |
+			      S_IWOTH |
+			      S_IXUSR |
+			      S_IXGRP |
+			      S_IXOTH |
+			      S_ISGID), 0) {
+		log_stderr("failure: fchmod");
+		goto out;
+	}
+
+	/* Verify that the sid bits got raised. */
+	if (!is_setgid(info->t_dir1_fd, "", AT_EMPTY_PATH)) {
+		log_stderr("failure: is_setgid");
+		goto out;
+	}
+
+	/* Changing mount properties on a detached mount. */
+	attr.userns_fd	= get_userns_fd(0, 10000, 10000);
+	if (attr.userns_fd < 0) {
+		log_stderr("failure: get_userns_fd");
+		goto out;
+	}
+
+	open_tree_fd = sys_open_tree(info->t_dir1_fd, "",
+				     AT_EMPTY_PATH |
+				     AT_NO_AUTOMOUNT |
+				     AT_SYMLINK_NOFOLLOW |
+				     OPEN_TREE_CLOEXEC |
+				     OPEN_TREE_CLONE);
+	if (open_tree_fd < 0) {
+		log_stderr("failure: sys_open_tree");
+		goto out;
+	}
+
+	if (sys_mount_setattr(open_tree_fd, "", AT_EMPTY_PATH, &attr, sizeof(attr))) {
+		log_stderr("failure: sys_mount_setattr");
+		goto out;
+	}
+
+	supported = openat_tmpfile_supported(open_tree_fd);
+
+	/* Only umask with S_IXGRP because inode strip S_ISGID will check mode
+	 * whether has group execute or search permission.
+	 */
+	umask(S_IXGRP);
+	mode = umask(S_IXGRP);
+	if (!(mode & S_IXGRP))
+		die("failure: umask");
+
+	/*
+	 * Below we verify that setgid inheritance for a newly created file or
+	 * directory works correctly. As part of this we need to verify that
+	 * newly created files or directories inherit their gid from their
+	 * parent directory. So we change the parent directorie's gid to 1000
+	 * and create a file with fs{g,u}id 0 and verify that the newly created
+	 * file and directory inherit gid 1000, not 0.
+	 */
+	if (fchownat(info->t_dir1_fd, "", -1, 1000, AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) {
+		log_stderr("failure: fchownat");
+		goto out;
+	}
+
+	pid = fork();
+	if (pid < 0) {
+		log_stderr("failure: fork");
+		goto out;
+	}
+	if (pid == 0) {
+		if (!caps_supported()) {
+			log_debug("skip: capability library not installed");
+			exit(EXIT_SUCCESS);
+		}
+
+		if (!switch_userns(attr.userns_fd, 0, 0, false))
+			die("failure: switch_userns");
+
+		if (!caps_down_fsetid())
+			die("failure: caps_down_fsetid");
+
+		/* create regular file via open() */
+		file1_fd = openat(open_tree_fd, FILE1, O_CREAT | O_EXCL | O_CLOEXEC, S_IXGRP | S_ISGID);
+		if (file1_fd < 0)
+			die("failure: create");
+
+		/* Neither in_group_p() nor capable_wrt_inode_uidgid() so setgid
+		 * bit needs to be stripped.
+		 */
+		if (is_setgid(open_tree_fd, FILE1, 0))
+			die("failure: is_setgid");
+
+		if (is_ixgrp(open_tree_fd, FILE1, 0))
+			die("failure: is_ixgrp");
+
+		/* create directory */
+		if (mkdirat(open_tree_fd, DIR1, 0000))
+			die("failure: create");
+
+		if (xfs_irix_sgid_inherit_enabled(info->t_fstype)) {
+			/* We're not in_group_p(). */
+			if (is_setgid(open_tree_fd, DIR1, 0))
+				die("failure: is_setgid");
+		} else {
+			/* Directories always inherit the setgid bit. */
+			if (!is_setgid(open_tree_fd, DIR1, 0))
+				die("failure: is_setgid");
+		}
+
+		if (is_ixgrp(open_tree_fd, DIR1, 0))
+			die("failure: is_ixgrp");
+
+		/* create a special file via mknodat() vfs_create */
+		if (mknodat(open_tree_fd, FILE2, S_IFREG | S_ISGID | S_IXGRP, 0))
+			die("failure: mknodat");
+
+		if (is_setgid(open_tree_fd, FILE2, 0))
+			die("failure: is_setgid");
+
+		if (is_ixgrp(open_tree_fd, FILE2, 0))
+			die("failure: is_ixgrp");
+
+		/* create a whiteout device via mknodat() vfs_mknod */
+		if (mknodat(open_tree_fd, CHRDEV1, S_IFCHR | S_ISGID | S_IXGRP, 0))
+			die("failure: mknodat");
+
+		if (is_setgid(open_tree_fd, CHRDEV1, 0))
+			die("failure: is_setgid");
+
+		if (is_ixgrp(open_tree_fd, CHRDEV1, 0))
+			die("failure: is_ixgrp");
+
+		/*
+		 * In setgid directories newly created files always inherit the
+		 * gid from the parent directory. Verify that the file is owned
+		 * by gid 1000, not by gid 0.
+		 */
+		if (!expected_uid_gid(open_tree_fd, FILE1, 0, 0, 1000))
+			die("failure: check ownership");
+
+		/*
+		 * In setgid directories newly created directories always
+		 * inherit the gid from the parent directory. Verify that the
+		 * directory is owned by gid 1000, not by gid 0.
+		 */
+		if (!expected_uid_gid(open_tree_fd, DIR1, 0, 0, 1000))
+			die("failure: check ownership");
+
+		if (!expected_uid_gid(open_tree_fd, FILE2, 0, 0, 1000))
+			die("failure: check ownership");
+
+		if (!expected_uid_gid(open_tree_fd, CHRDEV1, 0, 0, 1000))
+			die("failure: check ownership");
+
+		if (unlinkat(open_tree_fd, FILE1, 0))
+			die("failure: delete");
+
+		if (unlinkat(open_tree_fd, DIR1, AT_REMOVEDIR))
+			die("failure: delete");
+
+		if (unlinkat(open_tree_fd, FILE2, 0))
+			die("failure: delete");
+
+		if (unlinkat(open_tree_fd, CHRDEV1, 0))
+			die("failure: delete");
+
+		/* create tmpfile via filesystem tmpfile api */
+		if (supported) {
+			tmpfile_fd = openat(open_tree_fd, ".", O_TMPFILE | O_RDWR, S_IXGRP | S_ISGID);
+			if (tmpfile_fd < 0)
+				die("failure: create");
+			/* link the temporary file into the filesystem, making it permanent */
+			snprintf(path, PATH_MAX,  "/proc/self/fd/%d", tmpfile_fd);
+			if (linkat(AT_FDCWD, path, open_tree_fd, FILE3, AT_SYMLINK_FOLLOW))
+				die("failure: linkat");
+			if (close(tmpfile_fd))
+				die("failure: close");
+			if (is_setgid(open_tree_fd, FILE3, 0))
+				die("failure: is_setgid");
+			if (is_ixgrp(open_tree_fd, FILE3, 0))
+				die("failure: is_ixgrp");
+			if (!expected_uid_gid(open_tree_fd, FILE3, 0, 0, 1000))
+				die("failure: check ownership");
+			if (unlinkat(open_tree_fd, FILE3, 0))
+				die("failure: delete");
+		}
+
+		exit(EXIT_SUCCESS);
+	}
+	if (wait_for_pid(pid))
+		goto out;
+
+	fret = 0;
+	log_debug("Ran test");
+out:
+	safe_close(attr.userns_fd);
+	safe_close(file1_fd);
+	safe_close(open_tree_fd);
+
+	return fret;
+}
+
 static const struct test_struct t_idmapped_mounts[] = {
 	{ acls,                                                         true,   "posix acls on regular mounts",                                                                 },
 	{ create_in_userns,                                             true,   "create operations in user namespace",                                                          },
@@ -7745,3 +8164,13 @@ const struct test_suite s_setxattr_fix_705191b03d50 = {
 	.tests = t_setxattr_fix_705191b03d50,
 	.nr_tests = ARRAY_SIZE(t_setxattr_fix_705191b03d50),
 };
+
+static const struct test_struct t_setgid_create_umask_idmapped[] = {
+	{ setgid_create_umask_idmapped,					T_REQUIRE_IDMAPPED_MOUNTS,	"create operations by using umask in directories with setgid bit set on idmapped mount",		},
+	{ setgid_create_umask_idmapped_in_userns,			T_REQUIRE_IDMAPPED_MOUNTS,	"create operations by using umask in directories with setgid bit set on idmapped mount inside userns",	},
+};
+
+const struct test_suite s_setgid_create_umask_idmapped = {
+	.tests = t_setgid_create_umask_idmapped,
+	.nr_tests = ARRAY_SIZE(t_setgid_create_umask_idmapped),
+};
diff --git a/src/vfs/idmapped-mounts.h b/src/vfs/idmapped-mounts.h
index ff21ea2c..a332439f 100644
--- a/src/vfs/idmapped-mounts.h
+++ b/src/vfs/idmapped-mounts.h
@@ -14,5 +14,6 @@ extern const struct test_suite s_fscaps_in_ancestor_userns;
 extern const struct test_suite s_nested_userns;
 extern const struct test_suite s_setattr_fix_968219708108;
 extern const struct test_suite s_setxattr_fix_705191b03d50;
+extern const struct test_suite s_setgid_create_umask_idmapped;
 
 #endif /* __IDMAPPED_MOUNTS_H */
diff --git a/src/vfs/utils.c b/src/vfs/utils.c
index 1388edda..6db7a11d 100644
--- a/src/vfs/utils.c
+++ b/src/vfs/utils.c
@@ -809,6 +809,20 @@ bool is_sticky(int dfd, const char *path, int flags)
 	return (st.st_mode & S_ISVTX) > 0;
 }
 
+/*is_ixgrp - check whether file or directory is S_IXGRP */
+bool is_ixgrp(int dfd, const char *path, int flags)
+{
+	int ret;
+	struct stat st;
+
+	ret = fstatat(dfd, path, &st, flags);
+	if (ret < 0)
+		return false;
+
+	errno = 0; /* Don't report misleading errno. */
+	return (st.st_mode & S_IXGRP);
+}
+
 bool switch_resids(uid_t uid, gid_t gid)
 {
 	if (setresgid(gid, gid, gid))
diff --git a/src/vfs/utils.h b/src/vfs/utils.h
index 7fb702fd..c0dbe370 100644
--- a/src/vfs/utils.h
+++ b/src/vfs/utils.h
@@ -368,6 +368,7 @@ extern bool expected_file_size(int dfd, const char *path, int flags,
 extern bool is_setid(int dfd, const char *path, int flags);
 extern bool is_setgid(int dfd, const char *path, int flags);
 extern bool is_sticky(int dfd, const char *path, int flags);
+extern bool is_ixgrp(int dfd, const char *path, int flags);
 extern bool openat_tmpfile_supported(int dirfd);
 
 #endif /* __IDMAP_UTILS_H */
diff --git a/src/vfs/vfstest.c b/src/vfs/vfstest.c
index 29ac0bec..8448362e 100644
--- a/src/vfs/vfstest.c
+++ b/src/vfs/vfstest.c
@@ -1733,6 +1733,186 @@ out:
 	return fret;
 }
 
+/* The current_umask() is stripped from the mode directly in the vfs if the
+ * filesystem either doesn't support acls or the filesystem has been
+ * mounted without posic acl support.
+ *
+ * If the filesystem does support acls then current_umask() stripping is
+ * deferred to posix_acl_create(). So when the filesystem calls
+ * posix_acl_create() and there are no acls set or not supported then
+ * current_umask() will be stripped.
+ *
+ * Use umask(S_IXGRP) to check whether inode strip S_ISGID works correctly.
+ */
+
+static int setgid_create_umask(const struct vfstest_info *info)
+{
+	int fret = -1;
+	int file1_fd = -EBADF;
+	int tmpfile_fd = -EBADF;
+	pid_t pid;
+	bool supported = false;
+	mode_t mode;
+
+	if (!caps_supported())
+		return 0;
+
+	if (fchmod(info->t_dir1_fd, S_IRUSR |
+			      S_IWUSR |
+			      S_IRGRP |
+			      S_IWGRP |
+			      S_IROTH |
+			      S_IWOTH |
+			      S_IXUSR |
+			      S_IXGRP |
+			      S_IXOTH |
+			      S_ISGID), 0) {
+		log_stderr("failure: fchmod");
+		goto out;
+	}
+
+	/* Verify that the setgid bit got raised. */
+	if (!is_setgid(info->t_dir1_fd, "", AT_EMPTY_PATH)) {
+		log_stderr("failure: is_setgid");
+		goto out;
+	}
+
+	supported = openat_tmpfile_supported(info->t_dir1_fd);
+
+	/* Only umask with S_IXGRP because inode strip S_ISGID will check mode
+	 * whether has group execute or search permission.
+	 */
+	umask(S_IXGRP);
+	mode = umask(S_IXGRP);
+	if (!(mode & S_IXGRP))
+		die("failure: umask");
+
+	pid = fork();
+	if (pid < 0) {
+		log_stderr("failure: fork");
+		goto out;
+	}
+	if (pid == 0) {
+		if (!switch_ids(0, 10000))
+			die("failure: switch_ids");
+
+		if (!caps_down_fsetid())
+			die("failure: caps_down_fsetid");
+
+		/* create regular file via open() */
+		file1_fd = openat(info->t_dir1_fd, FILE1, O_CREAT | O_EXCL | O_CLOEXEC, S_IXGRP | S_ISGID);
+		if (file1_fd < 0)
+			die("failure: create");
+
+		/* Neither in_group_p() nor capable_wrt_inode_uidgid() so setgid
+		 * bit needs to be stripped.
+		 */
+		if (is_setgid(info->t_dir1_fd, FILE1, 0))
+			die("failure: is_setgid");
+
+		if (is_ixgrp(info->t_dir1_fd, FILE1, 0))
+			die("failure: is_ixgrp");
+
+		if (mkdirat(info->t_dir1_fd, DIR1, 0000))
+			die("failure: create");
+
+		if (xfs_irix_sgid_inherit_enabled(info->t_fstype)) {
+			/* We're not in_group_p(). */
+			if (is_setgid(info->t_dir1_fd, DIR1, 0))
+				die("failure: is_setgid");
+		} else {
+			/* Directories always inherit the setgid bit. */
+			if (!is_setgid(info->t_dir1_fd, DIR1, 0))
+				die("failure: is_setgid");
+		}
+
+		if (is_ixgrp(info->t_dir1_fd, DIR1, 0))
+			die("failure: is_ixgrp");
+
+		/* create a special file via mknodat() vfs_create */
+		if (mknodat(info->t_dir1_fd, FILE2, S_IFREG | S_ISGID | S_IXGRP, 0))
+			die("failure: mknodat");
+
+		if (is_setgid(info->t_dir1_fd, FILE2, 0))
+			die("failure: is_setgid");
+
+		if (is_ixgrp(info->t_dir1_fd, FILE2, 0))
+			die("failure: is_ixgrp");
+
+		/* create a character device via mknodat() vfs_mknod */
+		if (mknodat(info->t_dir1_fd, CHRDEV1, S_IFCHR | S_ISGID | S_IXGRP, makedev(5, 1)))
+			die("failure: mknodat");
+
+		if (is_setgid(info->t_dir1_fd, CHRDEV1, 0))
+			die("failure: is_setgid");
+
+		if (is_ixgrp(info->t_dir1_fd, CHRDEV1, 0))
+			die("failure: is_ixgrp");
+
+		/*
+		 * In setgid directories newly created files always inherit the
+		 * gid from the parent directory. Verify that the file is owned
+		 * by gid 0, not by gid 10000.
+		 */
+		if (!expected_uid_gid(info->t_dir1_fd, FILE1, 0, 0, 0))
+			die("failure: check ownership");
+
+		/*
+		 * In setgid directories newly created directories always
+		 * inherit the gid from the parent directory. Verify that the
+		 * directory is owned by gid 0, not by gid 10000.
+		 */
+		if (!expected_uid_gid(info->t_dir1_fd, DIR1, 0, 0, 0))
+			die("failure: check ownership");
+
+		if (!expected_uid_gid(info->t_dir1_fd, FILE2, 0, 0, 0))
+			die("failure: check ownership");
+
+		if (!expected_uid_gid(info->t_dir1_fd, CHRDEV1, 0, 0, 0))
+			die("failure: check ownership");
+
+		if (unlinkat(info->t_dir1_fd, FILE1, 0))
+			die("failure: delete");
+
+		if (unlinkat(info->t_dir1_fd, DIR1, AT_REMOVEDIR))
+			die("failure: delete");
+
+		if (unlinkat(info->t_dir1_fd, FILE2, 0))
+			die("failure: delete");
+
+		if (unlinkat(info->t_dir1_fd, CHRDEV1, 0))
+			die("failure: delete");
+
+		/* create tmpfile via filesystem tmpfile api */
+		if (supported) {
+			tmpfile_fd = openat(info->t_dir1_fd, ".", O_TMPFILE | O_RDWR, S_IXGRP | S_ISGID);
+			if (tmpfile_fd < 0)
+				die("failure: create");
+			/* link the temporary file into the filesystem, making it permanent */
+			if (linkat(tmpfile_fd, "", info->t_dir1_fd, FILE3, AT_EMPTY_PATH))
+				die("failure: linkat");
+			if (close(tmpfile_fd))
+				die("failure: close");
+			if (is_setgid(info->t_dir1_fd, FILE3, 0))
+				die("failure: is_setgid");
+			if (is_ixgrp(info->t_dir1_fd, FILE3, 0))
+				die("failure: is_ixgrp");
+			if (unlinkat(info->t_dir1_fd, FILE3, 0))
+				die("failure: delete");
+		}
+
+		exit(EXIT_SUCCESS);
+	}
+	if (wait_for_pid(pid))
+		goto out;
+
+	fret = 0;
+	log_debug("Ran test");
+out:
+	safe_close(file1_fd);
+	return fret;
+}
+
 static int setattr_truncate(const struct vfstest_info *info)
 {
 	int fret = -1;
@@ -1807,6 +1987,7 @@ static void usage(void)
 	fprintf(stderr, "--test-btrfs                        Run btrfs specific idmapped mount testsuite\n");
 	fprintf(stderr, "--test-setattr-fix-968219708108     Run setattr regression tests\n");
 	fprintf(stderr, "--test-setxattr-fix-705191b03d50    Run setxattr regression tests\n");
+	fprintf(stderr, "--test-setgid-create-umask          Run setgid with umask tests\n");
 
 	_exit(EXIT_SUCCESS);
 }
@@ -1825,6 +2006,7 @@ static const struct option longopts[] = {
 	{"test-btrfs",				no_argument,		0,	'b'},
 	{"test-setattr-fix-968219708108",	no_argument,		0,	'i'},
 	{"test-setxattr-fix-705191b03d50",	no_argument,		0,	'j'},
+	{"test-setgid-create-umask",		no_argument,		0,	'u'},
 	{NULL,					0,			0,	  0},
 };
 
@@ -1850,6 +2032,15 @@ static const struct test_suite s_basic = {
 	.nr_tests = ARRAY_SIZE(t_basic),
 };
 
+static const struct test_struct t_setgid_create_umask[] = {
+	{ setgid_create_umask,						0,			"create operations in directories with setgid bit set under umask",				},
+};
+
+static const struct test_suite s_setgid_create_umask = {
+	.tests = t_setgid_create_umask,
+	.nr_tests = ARRAY_SIZE(t_setgid_create_umask),
+};
+
 static bool run_test(struct vfstest_info *info, const struct test_struct suite[], size_t suite_size)
 {
 	int i;
@@ -1947,7 +2138,8 @@ int main(int argc, char *argv[])
 	bool idmapped_mounts_supported = false, test_btrfs = false,
 	     test_core = false, test_fscaps_regression = false,
 	     test_nested_userns = false, test_setattr_fix_968219708108 = false,
-	     test_setxattr_fix_705191b03d50 = false;
+	     test_setxattr_fix_705191b03d50 = false,
+	     test_setgid_create_umask = false;
 
 	init_vfstest_info(&info);
 
@@ -1989,6 +2181,9 @@ int main(int argc, char *argv[])
 		case 'j':
 			test_setxattr_fix_705191b03d50 = true;
 			break;
+		case 'u':
+			test_setgid_create_umask = true;
+			break;
 		case 'h':
 			/* fallthrough */
 		default:
@@ -2066,6 +2261,14 @@ int main(int argc, char *argv[])
 	    !run_suite(&info, &s_setxattr_fix_705191b03d50))
 		goto out;
 
+	if (test_setgid_create_umask) {
+		if (!run_suite(&info, &s_setgid_create_umask))
+			goto out;
+
+		if (!run_suite(&info, &s_setgid_create_umask_idmapped))
+			goto out;
+	}
+
 	fret = EXIT_SUCCESS;
 
 out:
diff --git a/tests/generic/691 b/tests/generic/691
new file mode 100755
index 00000000..d4875854
--- /dev/null
+++ b/tests/generic/691
@@ -0,0 +1,40 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2022 Fujitsu Limited. All Rights Reserved.
+#
+# FS QA Test No. 691
+#
+# Test that idmapped mounts setgid's behave correctly when using
+# umask(S_IXGRP)
+#
+. ./common/preamble
+_begin_fstest auto quick cap idmapped mount perms rw unlink
+
+# Import common functions.
+. ./common/filter
+
+# real QA test starts here
+
+_supported_fs generic
+_require_test
+_require_scratch
+
+echo "Silence is golden"
+
+$here/src/vfs/vfstest --test-setgid-create-umask \
+        --device "$TEST_DEV" --mount "$TEST_DIR" --fstype "$FSTYP"
+
+_scratch_mkfs > "$seqres.full" 2>&1
+export MOUNT_OPTIONS="-o noacl"
+
+# If filesystem supports noacl mount option, also test setgid bit whether
+# was stripped correctly.
+# noacl will earse acl flag in superblock, so kernel will use current_umask
+# in vfs directly instead of calling posix_acl_create on underflying
+# filesystem.
+_try_scratch_mount >>$seqres.full 2>&1 && \
+	$here/src/vfs/vfstest --test-setgid-create-umask \
+        --device "$SCRATCH_DEV" --mount "$SCRATCH_MNT" --fstype "$FSTYP"
+
+status=0
+exit
diff --git a/tests/generic/691.out b/tests/generic/691.out
new file mode 100644
index 00000000..006aef43
--- /dev/null
+++ b/tests/generic/691.out
@@ -0,0 +1,2 @@
+QA output created by 691
+Silence is golden
-- 
2.27.0


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