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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 21 Mar 2023 11:48:17 -0700
Message-ID: <CAHk-=wh1b0r+5SnwWedx=J4aZhRif1HLN_moxEG9Jzy23S6QUA@mail.gmail.com>
Subject: Re: [GIT PULL] keys: Miscellaneous fixes/changes
To:     David Howells <dhowells@redhat.com>, Jens Axboe <axboe@kernel.dk>
Cc:     Jarkko Sakkinen <jarkko@kernel.org>,
        Bharath SM <bharathsm@microsoft.com>,
        Shyam Prasad N <nspmangalore@gmail.com>,
        Steve French <smfrench@gmail.com>,
        Robbie Harwood <rharwood@redhat.com>,
        Eric Biederman <ebiederm@xmission.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        keyrings@vger.kernel.org, linux-cifs@vger.kernel.org,
        linux-crypto@vger.kernel.org, kexec@lists.infradead.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
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On Tue, Mar 21, 2023 at 9:43=E2=80=AFAM David Howells <dhowells@redhat.com>=
 wrote:
>
>  (1) Fix request_key() so that it doesn't cache a looked up key on the
>      current thread if that thread is a kernel thread.  The cache is
>      cleared during notify_resume - but that doesn't happen in kernel
>      threads.  This is causing cifs DNS keys to be un-invalidateable.

I've pulled this, but I'd like people to look a bit more at this.

The issue with TIF_NOTIFY_RESUME is that it is only done on return to
user space.

And these days, PF_KTHREAD isn't the only case that never returns to
user space. PF_IO_WORKER has the exact same behaviour.

Now, to counteract this, as of this merge window (and marked for
stable) IO threads do a fake "return to user mode" handling in
io_run_task_work(), and so I think we're all good, but I'd like people
to at least think about this.

              Linus