Re: Please consider backporting coredump %F patch to stable kernels

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Mon, Jun 02, 2025 at 01:45:02PM +0200, Christian Brauner wrote:
> On Mon, Jun 02, 2025 at 11:32:44AM +0200, Greg Kroah-Hartman wrote:
> > On Mon, Jun 02, 2025 at 11:09:05AM +0200, Christian Brauner wrote:
> > > On Fri, May 30, 2025 at 10:44:16AM +0100, Luca Boccassi wrote:
> > > > Dear stable maintainer(s),
> > > > 
> > > > The following series was merged for 6.16:
> > > > 
> > > > https://lore.kernel.org/all/20250414-work-coredump-v2-0-685bf231f828@kernel.org/
> > > > 
> > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c57f07b235871c9e5bffaccd458dca2d9a62b164
> > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=95c5f43181fe9c1b5e5a4bd3281c857a5259991f
> > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b5325b2a270fcaf7b2a9a0f23d422ca8a5a8bdea
> > > > 
> > > > This allows the userspace coredump handler to get a PIDFD referencing
> > > > the crashed process.
> > > > 
> > > > We have discovered that there are real world exploits that can be used
> > > > to trick coredump handling userspace software to act on foreign
> > > > processes due to PID reuse attacks:
> > > > 
> > > > https://security-tracker.debian.org/tracker/CVE-2025-4598
> > > > 
> > > > We have fixed the worst case scenario, but to really and
> > > > comprehensively fix the whole problem we need this new %F option. We
> > > > have backported the userspace side to the systemd stable branch. Would
> > > > it be possible to backport the above 3 patches to at least the 6.12
> > > > series, so that the next Debian stable can be fully covered? The first
> > > > two are small bug fixes so it would be good to have them, and the
> > > > third one is quite small and unless explicitly configured in the
> > > > core_pattern, it will be inert, so risk should be low.
> > > 
> > > I agree that we should try and backport this if Greg agrees we can do
> > > this. v6.15 will be easy to do. Further back might need some custom work
> > > though. Let's see what Greg thinks.
> > 
> > Yes, seems like a good thing to backport to at least 6.12.y if possible.
> > 
> > Is it just the above 3 commits?
> 
> Yes, just those three:
> 
> b5325b2a270f ("coredump: hand a pidfd to the usermode coredump helper")
> 95c5f43181fe ("coredump: fix error handling for replace_fd()")
> c57f07b23587 ("pidfs: move O_RDWR into pidfs_alloc_file()")
> 
> That should apply cleanly to v6.15 but for the others it requires custom
> backports. So here are a couple of trees all based on linux-*.*.y from
> the stable repo. You might need to adjust to your stable commit message
> format though:
> 
> v6.12:
> https://github.com/brauner/linux-stable/tree/vfs-6.12.coredump.pidfd

So that would be:
	git pull https://github.com/brauner/linux-stable.git vfs-6.12.coredump.pidfd
?

Can I get a signed tag so I know that I can trust a github.com account?

Also, 6.14.y didn't work all that well, let me see if I can get that to
work on my own like I did for 6.15.y (the pidfs patch needed to be
manually applied...)

thanks,

greg k-h