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

[Jarkko Sakkinen <jarkko@kernel.org>]

On Mon, Jun 08, 2026 at 08:42:21AM +0300, Jarkko Sakkinen wrote:
> On Mon, Jun 08, 2026 at 08:29:11AM +0300, Jarkko Sakkinen wrote:
> > 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?
> 
> Send v2 with the code changes that I proposed as we want to the change
> as ergonomic as possible.
> 
> Use this as the commit message:
> 
>     keys: Pin request_key_auth payload in instantiate paths
> 
>     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**
> 
>     Give request_key_auth payloads a refcount.  Take a payload reference while
>     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.
> 
>     [jarkko: Replaced the first two paragraphs of text with a concurrency scenario.]
> 
> And it includes also the remark at the end.
> 
> BR, Jarkko


Nothing heard so I pushed:

https://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-tpmdd.git/commit/?h=for-next-keys&id=9feb0bb3468e863b2b82a2eabfaeec4c7c44b90c

It has the commit message change.

BR, Jarkko