From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f68.google.com ([209.85.220.68]:32788 "EHLO mail-pa0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752355AbcFQUU5 (ORCPT ); Fri, 17 Jun 2016 16:20:57 -0400 From: Andrey Vagin To: linux-fsdevel@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Andrey Vagin , Alexander Viro , "Eric W. Biederman" Subject: [PATCH 0/2] [RFC] fs: allow to use dirfd as root for openat and other *at syscalls Date: Fri, 17 Jun 2016 13:20:46 -0700 Message-Id: <1466194848-13824-1-git-send-email-avagin@openvz.org> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: The problem is that a pathname can contain absolute symlinks and now they are resolved relative to the current root. If we want to open a file in another mount namespaces and we have a file descriptor to its root directory, we probably want to resolve pathname in the target mount namespace. Here are examples how we can open a file in a contex of another process. How we can do this without these changes: old_root = open("/", O_PATH); old_cwd = open(".", O_PATH); chroot("/proc/PID/root"); fd = open(pathname, O_RDONLY); fchdir(old_root); /* emulate fchroot() */ chroot("."); fchdir(old_cwd); close(old_cwd); close(old_root); How this code is simplified with new flags: dirfd = open("/proc/PID/root", O_PATH); fd = open(dirfd, pathname, O_RDONLY | O_ATROOT); close(dirfd); One more thing is that chroot isn't avaliable for unprivileged users. We met this problem, when we tryed to dump an ubuntu container and failed to resolve /proc/PID/root/var/run/mysqld/mysqld.sock, because /var/run was a symlink to /run. Cc: Alexander Viro Cc: "Eric W. Biederman" Signed-off-by: Andrey Vagin Andrey Vagin (2): namei: add LOOKUP_DFD_ROOT to use dfd as root fs: allow to use dirfd as root for openat and other *at syscalls fs/exec.c | 4 +++- fs/namei.c | 22 +++++++++++++++++----- fs/open.c | 6 +++++- fs/stat.c | 4 +++- fs/utimes.c | 4 +++- include/linux/namei.h | 2 ++ include/uapi/asm-generic/fcntl.h | 3 +++ include/uapi/linux/fcntl.h | 1 + 8 files changed, 37 insertions(+), 9 deletions(-) -- 2.5.5