From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan Metzmacher Subject: Re: IORING_REGISTER_CREDS[_UPDATE]() and credfd_create()? Date: Wed, 29 Jan 2020 14:11:02 +0100 Message-ID: <821243e7-b470-ad7a-c1a5-535bee58e76d@samba.org> References: <688e187a-75dd-89d9-921c-67de228605ce@samba.org> <1ac31828-e915-6180-cdb4-36685442ea75@kernel.dk> <0d4f43d8-a0c4-920b-5b8f-127c1c5a3fad@kernel.dk> <2d7e7fa2-e725-8beb-90b9-6476d48bdb33@gmail.com> <6c401e23-de7c-1fc1-4122-33d53fcf9700@kernel.dk> <35eebae7-76dd-52ee-58b2-4f9e85caee40@kernel.dk> <6e5ab6bf-6ff1-14df-1988-a80a7c6c9294@gmail.com> <2019e952-df2a-6b57-3571-73c525c5ba1a@kernel.dk> <0df4904f-780b-5d5f-8700-41df47a1b470@kernel.dk> <5406612e-299d-9d6e-96fc-c962eb93887f@gmail.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="RNLVW4EKoBAHUQUfqL7tZ7QYYQEGm1WCn" Return-path: In-Reply-To: <5406612e-299d-9d6e-96fc-c962eb93887f-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Pavel Begunkov , Jens Axboe Cc: io-uring , Linux API Mailing List List-Id: linux-api@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --RNLVW4EKoBAHUQUfqL7tZ7QYYQEGm1WCn Content-Type: multipart/mixed; boundary="viy5iQdNsiwmTYiYhyjIGXGXRbnYn1RAi"; protected-headers="v1" From: Stefan Metzmacher To: Pavel Begunkov , Jens Axboe Cc: io-uring , Linux API Mailing List Message-ID: <821243e7-b470-ad7a-c1a5-535bee58e76d-eUNUBHrolfbYtjvyW6yDsg@public.gmane.org> Subject: Re: IORING_REGISTER_CREDS[_UPDATE]() and credfd_create()? References: <688e187a-75dd-89d9-921c-67de228605ce-eUNUBHrolfbYtjvyW6yDsg@public.gmane.org> <1ac31828-e915-6180-cdb4-36685442ea75-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org> <0d4f43d8-a0c4-920b-5b8f-127c1c5a3fad-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org> <2d7e7fa2-e725-8beb-90b9-6476d48bdb33-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> <6c401e23-de7c-1fc1-4122-33d53fcf9700-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org> <35eebae7-76dd-52ee-58b2-4f9e85caee40-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org> <6e5ab6bf-6ff1-14df-1988-a80a7c6c9294-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> <2019e952-df2a-6b57-3571-73c525c5ba1a-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org> <0df4904f-780b-5d5f-8700-41df47a1b470-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org> <5406612e-299d-9d6e-96fc-c962eb93887f-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> In-Reply-To: <5406612e-299d-9d6e-96fc-c962eb93887f-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> --viy5iQdNsiwmTYiYhyjIGXGXRbnYn1RAi Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable Am 29.01.20 um 11:17 schrieb Pavel Begunkov: > On 29/01/2020 03:54, Jens Axboe wrote: >> On 1/28/20 5:24 PM, Jens Axboe wrote: >>> On 1/28/20 5:21 PM, Pavel Begunkov wrote: >>>> On 29/01/2020 03:20, Jens Axboe wrote: >>>>> On 1/28/20 5:10 PM, Pavel Begunkov wrote: >>>>>>>>> Checked out ("don't use static creds/mm assignments") >>>>>>>>> >>>>>>>>> 1. do we miscount cred refs? We grab one in get_current_cred() = for each async >>>>>>>>> request, but if (worker->creds !=3D work->creds) it will never = be put. >>>>>>>> >>>>>>>> Yeah I think you're right, that needs a bit of fixing up. >>>>>>> >>>>>> >>>>>> Hmm, it seems it leaks it unconditionally, as it grabs in a ref in= >>>>>> override_creds(). >>>>>> >>>>> >>>>> We grab one there, and an extra one. Then we drop one of them inlin= e, >>>>> and the other in __io_req_aux_free(). >>>>> >>>> Yeah, with the last patch it should make it even >>> >>> OK good we agree on that. I should probably pull back that bit to the= >>> original patch to avoid having a hole in there... >> >> Done >> >=20 > ("io_uring/io-wq: don't use static creds/mm assignments") and ("io_urin= g: > support using a registered personality for commands") looks good now. >=20 > Reviewed-by: Pavel Begunkov I'm very happy with the design, thanks! That exactly what I had in mind:-) It would also work with IORING_SETUP_SQPOLL, correct? However I think there're a few things to improve/simplify. > https://git.kernel.dk/cgit/linux-block/commit/?h=3Dfor-5.6/io_uring-vfs= &id=3Da26d26412e1e1783473f9dc8f030c3af3d54b1a6 In fs/io_uring.c mmgrab() and get_current_cred() are used together in two places, why is put_cred() called in __io_req_aux_free while mmdrop() is called from io_put_work(). I think both should be called in io_put_work(), that makes the code much easier to understand. My guess is that you choose __io_req_aux_free() for put_cred() because of the following patches, but I'll explain on the other commit why it's not needed. > https://git.kernel.dk/cgit/linux-block/commit/?h=3Dfor-5.6/io_uring-vfs= &id=3Dd9db233adf034bd7855ba06190525e10a05868be A minor one would be starting with 1 instead of 0 and using idr_alloc_cyclic() in order to avoid immediate reuse of ids. That way we could include the id in the tracing message and 0 would mean the current creds were used. > +static int io_remove_personalities(int id, void *p, void *data) > +{ > + struct io_ring_ctx *ctx =3D data; > + > + idr_remove(&ctx->personality_idr, id); Here we need something like: put_creds((const struct cred *)p); > + return 0; > +} The io_uring_register() calles would look like this, correct? id =3D io_uring_register(ring_fd, IORING_REGISTER_PERSONALITY, NULL, 0);= io_uring_register(ring_fd, IORING_UNREGISTER_PERSONALITY, NULL, id); > https://git.kernel.dk/cgit/linux-block/commit/?h=3Dfor-5.6/io_uring-vfs= &id=3Deec9e69e0ad9ad364e1b6a5dfc52ad576afee235 > + > + if (sqe_flags & IOSQE_PERSONALITY) { > + int id =3D READ_ONCE(sqe->personality); > + > + req->work.creds =3D idr_find(&ctx->personality_idr, id); > + if (unlikely(!req->work.creds)) { > + ret =3D -EINVAL; > + goto err_req; > + } > + get_cred(req->work.creds);> + old_creds =3D override_creds(req->wor= k.creds); > + } > + Here we could use a helper variable const struct cred *personality_creds; and leave req->work.creds as NULL. It means we can avoid the explicit get_cred() call and can skip the following hunk too: > @@ -3977,7 +3977,8 @@ static int io_req_defer_prep(struct io_kiocb *req= , > mmgrab(current->mm); > req->work.mm =3D current->mm; > } > - req->work.creds =3D get_current_cred(); > + if (!req->work.creds) > + req->work.creds =3D get_current_cred(); > =20 > switch (req->opcode) { > case IORING_OP_NOP: The override_creds(personality_creds) has changed current->cred and get_current_cred() will just pick it up as in the default case. This would make the patch much simpler and allows put_cred() to be in io_put_work() instead of __io_req_aux_free() as explained above. metze --viy5iQdNsiwmTYiYhyjIGXGXRbnYn1RAi-- --RNLVW4EKoBAHUQUfqL7tZ7QYYQEGm1WCn Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCgAdFiEEfFbGo3YXpfgryIw9DbX1YShpvVYFAl4xhGYACgkQDbX1YShp vVblORAAk3+0dsJ+7dJDj7s3cPMGwHImQCaRkJPDkVDd1pYf8/+IA1VNfqapN8jw wsyrPJp7nEy6+W/qtMciv0afEfCNlC6VdAiqWQOriI5qBMIrn8XPlq0+FGpjvUxd 6NrIbxPGsgq7NYiMzVhKyv1lC69OZtZ4rPNaI/QAwZMeyd699sy5al/yGzCaMJEv RWnrG6OSNvf/Snn2xrz7F3Ri/NJLoKrlA6DyKwWMbD2hygUqrX/wes3RV0cthvvE h3vYZbeyuhoNWoCx+nK7gizHuNzlT1eW9yJiEtZE6uToKUEVsey0Bf2qHu21MFA3 6Eri0m/EeD7GtNugb6hk4AQL7AtXWRbZotweefttYGPm+tQDtMWmaZA/er0Nk1La AbImJaWRCaoqXW77c1bzHNsWl9w6VZZrIAqv/cbumRg35Glqh5QbbqP4+nmeEupy vUvMkd2lctYWEPnUK2BVy4T0tzDhPxjANQ9dG94HFpUI6k9LSkXfl3TaOr/3ntAc M+/V02YF9IVX31IXrQX4U89BpDnsopfsa8hImBhdl+Y7Bmu7gsjlmOa5FOnIQx0N O0X3bxrvsU4UEWxPHtBsvqw7MNEnmMo5FjhDx7Lq8j//wSc58qUvqMQINghsWtHr l7YX0Q+Eig2KV9R/AXd8rzSwmeittDup4DiHm+geTV8RAEuB7xA= =WGgZ -----END PGP SIGNATURE----- --RNLVW4EKoBAHUQUfqL7tZ7QYYQEGm1WCn--