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Date:   Wed, 4 May 2022 18:57:28 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     "Gustavo A . R . Silva" <gustavoars@...nel.org>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Xiu Jianfeng <xiujianfeng@...wei.com>,
        Christian Göttsche <cgzones@...glemail.com>,
        netdev@...r.kernel.org, selinux@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        alsa-devel@...a-project.org, Al Viro <viro@...iv.linux.org.uk>,
        Andrew Gabbasov <andrew_gabbasov@...tor.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Gross <agross@...nel.org>,
        Andy Lavr <andy.lavr@...il.com>,
        Arend van Spriel <aspriel@...il.com>,
        Baowen Zheng <baowen.zheng@...igine.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Bradley Grove <linuxdrivers@...otech.com>,
        brcm80211-dev-list.pdl@...adcom.com,
        Christian Brauner <brauner@...nel.org>,
        Christian Lamparter <chunkeey@...glemail.com>,
        Chris Zankel <chris@...kel.net>,
        Cong Wang <cong.wang@...edance.com>,
        Daniel Axtens <dja@...ens.net>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Dan Williams <dan.j.williams@...el.com>,
        David Gow <davidgow@...gle.com>,
        David Howells <dhowells@...hat.com>,
        Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
        devicetree@...r.kernel.org, Dexuan Cui <decui@...rosoft.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        Eli Cohen <elic@...dia.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Eugeniu Rosca <erosca@...adit-jv.com>,
        Felipe Balbi <balbi@...nel.org>,
        Francis Laniel <laniel_francis@...vacyrequired.com>,
        Frank Rowand <frowand.list@...il.com>,
        Franky Lin <franky.lin@...adcom.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Gregory Greenman <gregory.greenman@...el.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Hante Meuleman <hante.meuleman@...adcom.com>,
        Hulk Robot <hulkci@...wei.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        James Morris <jmorris@...ei.org>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Jason Gunthorpe <jgg@...pe.ca>, Jens Axboe <axboe@...nel.dk>,
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        Keith Packard <keithp@...thp.com>, keyrings@...r.kernel.org,
        kunit-dev@...glegroups.com,
        Kuniyuki Iwashima <kuniyu@...zon.co.jp>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Lee Jones <lee.jones@...aro.org>,
        Leon Romanovsky <leon@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        linux1394-devel@...ts.sourceforge.net,
        linux-afs@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, linux-bluetooth@...r.kernel.org,
        linux-hardening@...r.kernel.org, linux-hyperv@...r.kernel.org,
        linux-integrity@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-scsi@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-wireless@...r.kernel.org,
        linux-xtensa@...ux-xtensa.org, llvm@...ts.linux.dev,
        Loic Poulain <loic.poulain@...aro.org>,
        Louis Peens <louis.peens@...igine.com>,
        Luca Coelho <luciano.coelho@...el.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        Marc Dionne <marc.dionne@...istor.com>,
        Marcel Holtmann <marcel@...tmann.org>,
        Mark Brown <broonie@...nel.org>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Max Filippov <jcmvbkbc@...il.com>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Muchun Song <songmuchun@...edance.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nuno Sá <nuno.sa@...log.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Rich Felker <dalias@...ifal.cx>,
        Rob Herring <robh+dt@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        SHA-cyfmac-dev-list@...ineon.com,
        Simon Horman <simon.horman@...igine.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Stefan Richter <stefanr@...6.in-berlin.de>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Tadeusz Struk <tadeusz.struk@...aro.org>,
        Takashi Iwai <tiwai@...e.com>, Tom Rix <trix@...hat.com>,
        Udipto Goswami <quic_ugoswami@...cinc.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        wcn36xx@...ts.infradead.org, Wei Liu <wei.liu@...nel.org>,
        xen-devel@...ts.xenproject.org,
        Yang Yingliang <yangyingliang@...wei.com>
Subject: Re: [PATCH 28/32] selinux: Use mem_to_flex_dup() with xfrm and sidtab

On Tue, May 3, 2022 at 9:57 PM Kees Cook <keescook@...omium.org> wrote:
>
> As part of the work to perform bounds checking on all memcpy() uses,
> replace the open-coded a deserialization of bytes out of memory into a
> trailing flexible array by using a flex_array.h helper to perform the
> allocation, bounds checking, and copying:
>
>     struct xfrm_sec_ctx
>     struct sidtab_str_cache
>
> Cc: Steffen Klassert <steffen.klassert@...unet.com>
> Cc: Herbert Xu <herbert@...dor.apana.org.au>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Paul Moore <paul@...l-moore.com>
> Cc: Stephen Smalley <stephen.smalley.work@...il.com>
> Cc: Eric Paris <eparis@...isplace.org>
> Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> Cc: Xiu Jianfeng <xiujianfeng@...wei.com>
> Cc: "Christian Göttsche" <cgzones@...glemail.com>
> Cc: netdev@...r.kernel.org
> Cc: selinux@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  include/uapi/linux/xfrm.h    | 4 ++--
>  security/selinux/ss/sidtab.c | 9 +++------
>  security/selinux/xfrm.c      | 7 ++-----
>  3 files changed, 7 insertions(+), 13 deletions(-)
>
> diff --git a/include/uapi/linux/xfrm.h b/include/uapi/linux/xfrm.h
> index 65e13a099b1a..4a6fa2beff6a 100644
> --- a/include/uapi/linux/xfrm.h
> +++ b/include/uapi/linux/xfrm.h
> @@ -31,9 +31,9 @@ struct xfrm_id {
>  struct xfrm_sec_ctx {
>         __u8    ctx_doi;
>         __u8    ctx_alg;
> -       __u16   ctx_len;
> +       __DECLARE_FLEX_ARRAY_ELEMENTS_COUNT(__u16, ctx_len);
>         __u32   ctx_sid;
> -       char    ctx_str[0];
> +       __DECLARE_FLEX_ARRAY_ELEMENTS(char, ctx_str);
>  };

While I like the idea of this in principle, I'd like to hear about the
testing you've done on these patches.  A previous flex array
conversion in the audit uapi headers ended up causing a problem with
GCC12 and SWIG; while it was a SWIG problem and not a kernel header
problem that was thin consolation for those with broken builds.

> diff --git a/security/selinux/ss/sidtab.c b/security/selinux/ss/sidtab.c
> index a54b8652bfb5..a9d434e8cff7 100644
> --- a/security/selinux/ss/sidtab.c
> +++ b/security/selinux/ss/sidtab.c
> @@ -23,8 +23,8 @@ struct sidtab_str_cache {
>         struct rcu_head rcu_member;
>         struct list_head lru_member;
>         struct sidtab_entry *parent;
> -       u32 len;
> -       char str[];
> +       DECLARE_FLEX_ARRAY_ELEMENTS_COUNT(u32, len);
> +       DECLARE_FLEX_ARRAY_ELEMENTS(char, str);
>  };
>
>  #define index_to_sid(index) ((index) + SECINITSID_NUM + 1)

-- 
paul-moore.com

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