Messages in this thread | | | From | Andrey Vagin <> | 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 |
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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 <viro@zeniv.linux.org.uk> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Andrey Vagin <avagin@openvz.org>
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
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