Re: [PATCH v3 1/2] exec: add PR_HIDE_SELF_EXE prctl

[Colin Walters]

On Sun, Jan 29, 2023, at 11:58 AM, Christian Brauner wrote:
> On Sun, Jan 29, 2023 at 08:59:32AM -0500, Colin Walters wrote:
>> 
>> 
>> On Wed, Jan 25, 2023, at 11:30 AM, Giuseppe Scrivano wrote:
>> > 
>> > After reading some comments on the LWN.net article, I wonder if
>> > PR_HIDE_SELF_EXE should apply to CAP_SYS_ADMIN in the initial user
>> > namespace or if in this case root should keep the privilege to inspect
>> > the binary of a process.  If a container runs with that many privileges
>> > then it has already other ways to damage the host anyway.
>> 
>> Right, that's what I was trying to express with the "make it work the same as map_files".  Hiding the entry entirely even for initial-namespace-root (real root) seems like it's going to potentially confuse profiling/tracing/debugging tools for no good reason.
>
> If this can be circumvented via CAP_SYS_ADMIN 

To be clear, I'm proposing CAP_SYS_ADMIN in the current user namespace at the time of the prctl().  (Or if keeping around a reference just for this is too problematic, perhaps hardcoding to the init ns)

A process with CAP_SYS_ADMIN in a child namespace would still not be able to read the binary.

> then this mitigation
> becomes immediately way less interesting because the userspace
> mitigation we came up with protects against CAP_SYS_ADMIN as well
> without any regression risk. 

The userspace mitigation here being "clone self to memfd"?  But that's a sufficiently ugly workaround that it's created new problems; see https://lwn.net/Articles/918106/