Re: [PATCH] keys: Pin request_key_auth payload in instantiate paths

[Jarkko Sakkinen <jarkko@kernel.org>]

On Mon, Jun 08, 2026 at 06:10:23AM +0300, Jarkko Sakkinen wrote:
> On Mon, Jun 08, 2026 at 06:06:21AM +0300, Jarkko Sakkinen wrote:
> > On Tue, May 26, 2026 at 10:48:38AM +0800, Shaomin Chen wrote:
> > > keyctl_instantiate_key_common() reads request_key_auth from the assumed
> > > auth key before copying an instantiation payload from userspace.  The copy
> > > can fault and sleep.  If the request completes and revokes the auth key in
> > > that window, the auth payload can be detached and freed before the
> > > instantiate path uses it again.
> > > 
> > > A request-key helper reproducer can trigger this race.  One helper child
> > > blocks in KEYCTL_INSTANTIATE_IOV while the original helper instantiates the
> > > requested key and returns.  KASAN then reports a use-after-free from the
> > > stale request_key_auth payload in keyctl_instantiate_key_common().
> > > 
> > > Give request_key_auth payloads a refcount.  Take a payload reference while
> > 
> > Please, name concrete things accurately. I.e. 'usage' in this case. If
> > you have a name, use it instead of obfuscating generalizations.
> > 
> > > authkey->sem stabilizes the payload and revocation state.  Hold that
> > > reference across the instantiate and reject paths.  Drop the auth key
> > > owning reference from revoke and destroy.
> > > 
> > > Reported-by: Shaomin Chen <eeesssooo020@gmail.com>
> > > Closes: https://lore.kernel.org/r/20260519144403.436694-1-eeesssooo020@gmail.com
> > > Signed-off-by: Shaomin Chen <eeesssooo020@gmail.com>
> > > ---
> > >  include/keys/request_key_auth-type.h |  2 ++
> > >  security/keys/internal.h             |  2 ++
> > >  security/keys/keyctl.c               | 24 +++++++++++++++-----
> > >  security/keys/request_key_auth.c     | 33 ++++++++++++++++++++++++++--
> > >  4 files changed, 53 insertions(+), 8 deletions(-)
> > 
> > So first, couple of things.
> > 
> > I'm not going to test not that well documented involving OOT driver.
> 
> Oops, sorry typo. "not that well documented reproducer" :-)
> 
> But it is cool we just then need to draw the picture.

I think I got this:

A: request_key()       B: KEYCTL_INSTANTIATE_IOV
----------------       -------------------------
create auth key
store rka in auth key
wait for helper
                       get auth key
                       load rka from auth key
                       copy user payload
                       sleep on #PF
helper completed
detach and free rka
destroy auth key
                       wake up
                       use rka->target_key
                       **USE-AFTER-FREE**

So nothing really complicated here, is there?
`
BR, Jarkko