On 09/01/2019 00:30, Kees Cook wrote: > On Tue, Jan 8, 2019 at 5:29 AM Mickaël Salaün > <mickael.salaun@xxxxxxxxxxx> wrote: >> >> >> On 03/01/2019 12:17, Jann Horn wrote: >>> On Thu, Dec 13, 2018 at 3:49 PM Mickaël Salaün >>> <mickael.salaun@xxxxxxxxxxx> wrote: >>>> On 12/12/2018 18:09, Jann Horn wrote: >>>>> On Wed, Dec 12, 2018 at 9:18 AM Mickaël Salaün <mic@xxxxxxxxxxx> wrote: >>>>>> Enable to either propagate the mount options from the underlying VFS >>>>>> mount to prevent execution, or to propagate the file execute permission. >>>>>> This may allow a script interpreter to check execution permissions >>>>>> before reading commands from a file. >>>>>> >>>>>> The main goal is to be able to protect the kernel by restricting >>>>>> arbitrary syscalls that an attacker could perform with a crafted binary >>>>>> or certain script languages. It also improves multilevel isolation >>>>>> by reducing the ability of an attacker to use side channels with >>>>>> specific code. These restrictions can natively be enforced for ELF >>>>>> binaries (with the noexec mount option) but require this kernel >>>>>> extension to properly handle scripts (e.g., Python, Perl). > > I like this idea, but I think it shouldn't live in Yama (since it is > currently intended to be a ptrace-policy-only LSM). It was > _originally_ designed to do various DAC improvements, but the > agreement was that those should live directly in the VFS instead (i.e. > the symlink, hardlink and now fifo and regular file defenses). > > This should likely go in similarly. (But if not, it could also be its own LSM.) > I think that Yama is quite handy and make sense here, but I'm fine putting this knob elsewhere. However, I was thinking, for a future patch series, to add another sysctl to lock this choice, i.e. generalizing the way Yama can lock the ptrace_scope. What matter here is the ability for an LSM to use this O_MAYEXEC flag. Yama is a good place to showcase this feature and I think it is cleaner to leverage the LSM framework to put new (optional) security features. I can easily create a new LSM but it would be pretty similar to Yama... What do you think about it James and Al? Side question: wouldn't it be better to use a 0600 mode (instead of 0644) for this kind of sysctl?
