Re: [RFC PATCH 0/2] keys: Address lookup_user_key() mutability

[Serge Hallyn (AMD)]

On Mon, Oct 05, 2026 at 09:46:41PM +0300, Jarkko Sakkinen wrote:
> On Mon, Oct 05, 2026 at 08:09:24AM -0500, Serge E. Hallyn wrote:
> > On Sun, Oct 04, 2026 at 08:54:06PM +0300, Jarkko Sakkinen wrote:
> > > On Thu, Sep 24, 2026 at 08:55:16AM +0300, Jarkko Sakkinen wrote:
> > > > The main objective in these patches is to remove to unneeded mutability
> > > > from key look ups. It does harm and brings no value so it is pretty obvious
> > > > to me that addressing this harmful behaviour is what we should do.
> > > > 
> > > > I based the first patch on what Jann suggested in [1]. Nothing too clever here
> > > > and I'm ofc open for further suggestions.
> > > > 
> > > > [1] https://lore.kernel.org/keyrings/CAG48ez0XjVSR=M--UBauTm8sJuc+ZbhKzaPa3a6wrSVHyoKevw@xxxxxxxxxxxxxx/
> > > > 
> > > > Jarkko Sakkinen (2):
> > > >   keys: Return user session keyring on lookup
> > > >   keys: Reject keyring creation with overridden credentials
> > > > 
> > > >  Documentation/security/keys/core.rst |  7 ++-
> > > >  security/keys/process_keys.c         | 65 +++++++++++++++-------------
> > > >  2 files changed, 40 insertions(+), 32 deletions(-)
> > > > 
> > > > --
> > > > 2.47.3
> > > > 
> > > 
> > > So.. should I move forward to with non-RFC v2?
> > 
> > Patch 2 absolutely makes sense, "doc, it hurts when I do this", "don't do
> > that then."
> > 
> > Regarding patch 1, that seems like quite a change in behavior, right?  I
> > don't see any docs or comments that promise the current behavior, but
> > has any userspace or subsystem come to depend on it?  I guess that, if so,
> > then it just has to create a link to the user session keyring like pam
> > (according to what I've read) does?
> 
> Thanks a lot of responding.
> 
> I fully agree with you but I'd need help for evaluating things further.
> 
> 1/2 based on Jann's email about the topic and my interpretation of the
> suggestion. I neither used brains nor AI for this and consider the patch
> merely as a conversation starter (and what a great success it was on doing
> that) :-)

 :)

> All feedback is good feedback at this point. I need supporting code to
> remember/recall later on so at least this serves that purpose.
> 
> Br, Jarkko

I've been staring at the before and after code for a bit now.
It does even more than I was thinking :)  But I was trying to
detail the changed behavior (from userspace's pov), and after
several attempts, it seems maybe there actually isn't any.

Q: is there any path whereby the 

```
        else if (test_bit(KEY_FLAG_UID_KEYRING,
                                    &ctx.cred->session_keyring->flags) &&
                           lflags & KEY_LOOKUP_CREATE) {
```

case can still happen?  Or was this the only place where we installed
the user_session keyring as session keyring, so that we can drop this
branch?