On Tue, Jun 07, 2022 at 05:31:39PM +0200, Christian Göttsche wrote: > From: Miklos Szeredi <mszeredi@xxxxxxxxxx> > > Support file descriptors obtained via O_PATH for extended attribute > operations. > > Extended attributes are for example used by SELinux for the security > context of file objects. To avoid time-of-check-time-of-use issues while > setting those contexts it is advisable to pin the file in question and > operate on a file descriptor instead of the path name. This can be > emulated in userspace via /proc/self/fd/NN [1] but requires a procfs, > which might not be mounted e.g. inside of chroots, see[2]. > > [1]: https://github.com/SELinuxProject/selinux/commit/7e979b56fd2cee28f647376a7233d2ac2d12ca50 > [2]: https://github.com/SELinuxProject/selinux/commit/de285252a1801397306032e070793889c9466845 > > Original patch by Miklos Szeredi <mszeredi@xxxxxxxxxx> > https://patchwork.kernel.org/project/linux-fsdevel/patch/20200505095915.11275-6-mszeredi@xxxxxxxxxx/ > > > While this carries a minute risk of someone relying on the property of > > xattr syscalls rejecting O_PATH descriptors, it saves the trouble of > > introducing another set of syscalls. > > > > Only file->f_path and file->f_inode are accessed in these functions. > > > > Current versions return EBADF, hence easy to detect the presense of > > this feature and fall back in case it's missing. > > CC: linux-api@xxxxxxxxxxxxxxx > CC: linux-man@xxxxxxxxxxxxxxx > Signed-off-by: Christian Göttsche <cgzones@xxxxxxxxxxxxxx> > --- I'd be somewhat fine with getxattr and listxattr but I'm worried that setxattr/removexattr waters down O_PATH semantics even more. I don't want O_PATH fds to be useable for operations which are semantically equivalent to a write. In sensitive environments such as service management/container runtimes we often send O_PATH fds around precisely because it is restricted what they can be used for. I'd prefer to not to plug at this string.
