fs: Add missing umask strip in vfs_tmpfile

All creation paths except for O_TMPFILE handle umask in the vfs directly
if the filesystem doesn't support or enable POSIX ACLs. If the filesystem
does then umask handling is deferred until posix_acl_create().
Because, O_TMPFILE misses umask handling in the vfs it will not honor
umask settings. Fix this by adding the missing umask handling.

Link: https://lore.kernel.org/r/[email protected]
Fixes: 60545d0 ("[O_TMPFILE] it's still short a few helpers, but infrastructure should be OK now...")
Cc: <[email protected]> # 4.19+
Reported-by: Christian Brauner (Microsoft) <[email protected]>
Reviewed-by: Darrick J. Wong <[email protected]>
Reviewed-and-Tested-by: Jeff Layton <[email protected]>
Acked-by: Christian Brauner (Microsoft) <[email protected]>
Signed-off-by: Yang Xu <[email protected]>
Signed-off-by: Christian Brauner (Microsoft) <[email protected]>

Author: xuyang0410

fs/namei.c

@@ -3565,6 +3565,8 @@ struct dentry *vfs_tmpfile(struct user_namespace *mnt_userns,
 	child = d_alloc(dentry, &slash_name);
 	if (unlikely(!child))
 		goto out_err;
+	if (!IS_POSIXACL(dir))
+		mode &= ~current_umask();
 	error = dir->i_op->tmpfile(mnt_userns, dir, child, mode);
 	if (error)
 		goto out_err;