On Thu, May 28, 2020 at 04:17:00PM +0200, Christian Brauner wrote: > On Wed, May 27, 2020 at 06:59:54PM -0700, Kees Cook wrote: > > On Thu, May 28, 2020 at 01:16:46AM +0200, Christian Brauner wrote: > > > I'm also starting to think this isn't even possible or currently doable > > > safely. > > > The fdtable in the kernel would end up with a dangling pointer, I would > > > think. Unless you backtrack all fds that still have a reference into the > > > fdtable and refer to that file and close them all in the kernel which I > > > don't think is possible and also sounds very dodgy. This also really > > > seems like we would be breaking a major contract, namely that fds stay > > > valid until userspace calls close, execve(), or exits. > > > > Right, I think I was just using the wrong words? I was looking at it > > like a pipe, or a socket, where you still have an fd, but reads return > > 0, you might get SIGPIPE, etc. The VFS clearly knows what a > > "disconnected" fd is, and I had assumed there was general logic for it > > to indicate "I'm not here any more". > > > > I recently did something very similar to the pstore filesystem, but I got > > to cheat with some massive subsystem locks. In that case I needed to clear > > all the inodes out of the tmpfs, so I unlink them all and manage the data > > lifetimes pointing back into the (waiting to be unloaded) backend module > > by NULLing the pointer back, which is safe because of the how the locking > > there happens to work. Any open readers, when they close, will have the > > last ref count dropped, at which point the record itself is released too. > > > > Back to the seccomp subject: should "all tasks died" be distinguishable > > from "I can't find that notification" in the ioctl()? (i.e. is ENOENT > > sufficient, or does there need to be an EIO or ESRCH there?) > > I personally think it's fine as it is but as it might help users if we > reported ESRCH something like the patch below might do. > Actual cleanup of the notifier should still happen in > seccomp_notify_release() imho, and not in __poll_t both conceptually and > also because f_op->release() happens on finaly fput() which punts it to > task_work() which finishes when the task returns from kernel mode (or > exits) - or - if the task is not alive anymore just puts it on the > kernel global workqueue which is perfect for non-high-priority cleanup > stuff. It's better than making __poll_t heavier than it needs to be. > Unless there's an obvious reason not to. Scratch the patch I posted before here; it's garbage of course. _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
