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samedi 09 janvier 2016 (1 post)
  • linux-grsec in unstable

As some of you might have already noticed, linux-grsec entered Debian unstable earlier this week, following linux-grsec-base a bit earlier.

So that means, if you're running sid, you can just run:

# apt install linux-image-4.3.0-1-grsec-amd64

There's no metapackage (version-less) for now, but I might add one at one point, if people need it.

After installing the kernel and the linux-grsec-base support package, you should check the /etc/sysctl.d/grsec.conf file and review the various tunables there, which might or might not suit your needs. The settings are mostly all enabled in the package (in order to get a “secure by default” state), but there a few bits you might need to disable.

 For example, on my main laptop, where I do most of my stuff, including Debian work, I've disabled:

kernel.grsecurity.deny_new_usb = 0
kernel.grsecurity.audit_chdir = 0
kernel.grsecurity.chroot_deny_chmod = 0
kernel.grsecurity.chroot_deny_mknod = 0
kernel.pax.softmode = 0

The deny_new_usb because a laptop is not really usable without USB, audit_chdir because it's really to noisy (I like to keep exec_logging though, because it's only for the root gid so it's somehow interesting and not too noisy).

Both chroot settings are disabled because I'm building packages in pbuilder, which uses chroot. By the way, if you're doing that you'll need to add the pbuilder (uid 1234) user to the grsec-tpe (gid 64040) group inside the chroot so it has permissions to execute stuff.

softmode is disabled but it's a default setting (“secure by default”). You can use it if needed to see what PaX /would/ deny and adjust things (using paxctl or setting file extended attributes).

On the same laptop, I need to set PaX 'm' attributes (allow W|X memory maps) on the following binaries:

setfattr -n user.pax.flags -v m /usr/bin/evolution
setfattr -n user.pax.flags -v m /usr/bin/python
setfattr -n user.pax.flags -v m /usr/lib/chromium/chromium

It's a bit unfortunate (especially evolution and chromium are quite exposed to untrusted code, and python is really too generic), but to keep a working box I don't have much choice.

Plans regarding stable are a bit more fuzzy. As indicated on the initial bug, the current upstream release model doesn't really fit with the “Debian stable” one: only the test patch, against the latest major Linux kernel version, is available free of charge. I don't think the release team would be really happy to see a new Linux version uploaded to stable every two months.

Although having linux-grsec on unstable is already a great victory, I still think most users are likely to want it on stable (for example on server boxes), so I'm considering plans for that. Right now, I'm still uploading jessie packages to my repository, but also investigating wether backports are suitable. The default answer is no, obviously, because backports are only supposed to hosts packages which will be in the next stable release, but maybe there will be something possible. Stay tuned, in any way.

Don't hesitate to try the packages. There might be some roughs edges, it's expected. If you have issues, please read the documentation available on grsecurity and PaX, because security is a process, and installing the package won't just magically make you secure if you don't know what it does. Don't hesitate to report bugs, but try to investigate a bit before (with the src:linux package, and with vanilla+grsec packages).

Finally, many thanks to Brad Spengler and the PaX team, this is their work, I'm merely the packager here. 

Yves-Alexis@10:14:37 (Debian)

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