From: Kees Cook <keescook@chromium.org>
To: Tycho Andersen <tycho@tycho.ws>
Cc: LKML <linux-kernel@vger.kernel.org>,
Linux Containers <containers@lists.linux-foundation.org>,
Linux API <linux-api@vger.kernel.org>,
Andy Lutomirski <luto@amacapital.net>,
Oleg Nesterov <oleg@redhat.com>,
"Eric W . Biederman" <ebiederm@xmission.com>,
"Serge E . Hallyn" <serge@hallyn.com>,
Christian Brauner <christian.brauner@ubuntu.com>,
Tyler Hicks <tyhicks@canonical.com>,
Akihiro Suda <suda.akihiro@lab.ntt.co.jp>,
Jann Horn <jannh@google.com>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH v7 1/6] seccomp: add a return code to trap to userspace
Date: Wed, 17 Oct 2018 15:21:02 -0700 [thread overview]
Message-ID: <CAGXu5jK5yN7zcPUMzFYnUbRrVkLNE0YDCioYdNC3P6mF437+5g@mail.gmail.com> (raw)
In-Reply-To: <20181017202933.GB14047@cisco>
On Wed, Oct 17, 2018 at 1:29 PM, Tycho Andersen <tycho@tycho.ws> wrote:
> On Thu, Sep 27, 2018 at 02:31:24PM -0700, Kees Cook wrote:
>> On Thu, Sep 27, 2018 at 8:11 AM, Tycho Andersen <tycho@tycho.ws> wrote:
>> > @@ -60,4 +62,29 @@ struct seccomp_data {
>> > __u64 args[6];
>> > };
>> >
>> > +struct seccomp_notif {
>> > + __u16 len;
>> > + __u64 id;
>> > + __u32 pid;
>> > + __u8 signaled;
>> > + struct seccomp_data data;
>> > +};
>> > +
>> > +struct seccomp_notif_resp {
>> > + __u16 len;
>> > + __u64 id;
>> > + __s32 error;
>> > + __s64 val;
>> > +};
>>
>> So, len has to come first, for versioning. However, since it's ahead
>> of a u64, this leaves a struct padding hole. pahole output:
>>
>> struct seccomp_notif {
>> __u16 len; /* 0 2 */
>>
>> /* XXX 6 bytes hole, try to pack */
>>
>> __u64 id; /* 8 8 */
>> __u32 pid; /* 16 4 */
>> __u8 signaled; /* 20 1 */
>>
>> /* XXX 3 bytes hole, try to pack */
>>
>> struct seccomp_data data; /* 24 64 */
>> /* --- cacheline 1 boundary (64 bytes) was 24 bytes ago --- */
>>
>> /* size: 88, cachelines: 2, members: 5 */
>> /* sum members: 79, holes: 2, sum holes: 9 */
>> /* last cacheline: 24 bytes */
>> };
>> struct seccomp_notif_resp {
>> __u16 len; /* 0 2 */
>>
>> /* XXX 6 bytes hole, try to pack */
>>
>> __u64 id; /* 8 8 */
>> __s32 error; /* 16 4 */
>>
>> /* XXX 4 bytes hole, try to pack */
>>
>> __s64 val; /* 24 8 */
>>
>> /* size: 32, cachelines: 1, members: 4 */
>> /* sum members: 22, holes: 2, sum holes: 10 */
>> /* last cacheline: 32 bytes */
>> };
>>
>> How about making len u32, and moving pid and error above "id"? This
>> leaves a hole after signaled, so changing "len" won't be sufficient
>> for versioning here. Perhaps move it after data?
>
> Just to confirm my understanding; I've got these as:
>
> struct seccomp_notif {
> __u32 len; /* 0 4 */
> __u32 pid; /* 4 4 */
> __u64 id; /* 8 8 */
> __u8 signaled; /* 16 1 */
>
> /* XXX 7 bytes hole, try to pack */
>
> struct seccomp_data data; /* 24 64 */
> /* --- cacheline 1 boundary (64 bytes) was 24 bytes ago --- */
>
> /* size: 88, cachelines: 2, members: 5 */
> /* sum members: 81, holes: 1, sum holes: 7 */
> /* last cacheline: 24 bytes */
> };
> struct seccomp_notif_resp {
> __u32 len; /* 0 4 */
> __s32 error; /* 4 4 */
> __u64 id; /* 8 8 */
> __s64 val; /* 16 8 */
>
> /* size: 24, cachelines: 1, members: 4 */
> /* last cacheline: 24 bytes */
> };
>
> in the next version. Since the structure has no padding at the end of
> it, I think the Right Thing will happen. Note that this is slightly
> different than what Kees suggested, if I add signaled after data, then
> I end up with:
>
> struct seccomp_notif {
> __u32 len; /* 0 4 */
> __u32 pid; /* 4 4 */
> __u64 id; /* 8 8 */
> struct seccomp_data data; /* 16 64 */
> /* --- cacheline 1 boundary (64 bytes) was 16 bytes ago --- */
> __u8 signaled; /* 80 1 */
>
> /* size: 88, cachelines: 2, members: 5 */
> /* padding: 7 */
> /* last cacheline: 24 bytes */
> };
>
> which I think will have the versioning problem if the next member
> introduces is < 7 bytes.
It'll be a problem in either place. What I was thinking was that
specific versioning is required instead of just length.
-Kees
--
Kees Cook
Pixel Security
next prev parent reply other threads:[~2018-10-18 6:18 UTC|newest]
Thread overview: 91+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-27 15:11 [PATCH v7 0/6] seccomp trap to userspace Tycho Andersen
2018-09-27 15:11 ` [PATCH v7 1/6] seccomp: add a return code to " Tycho Andersen
2018-09-27 21:31 ` Kees Cook
2018-09-27 22:48 ` Tycho Andersen
2018-09-27 23:10 ` Kees Cook
2018-09-28 14:39 ` Tycho Andersen
2018-10-08 14:58 ` Christian Brauner
2018-10-09 14:28 ` Tycho Andersen
2018-10-09 16:24 ` Christian Brauner
2018-10-09 16:29 ` Tycho Andersen
2018-10-17 20:29 ` Tycho Andersen
2018-10-17 22:21 ` Kees Cook [this message]
2018-10-17 22:33 ` Tycho Andersen
2018-10-21 16:04 ` Tycho Andersen
2018-10-22 9:42 ` Christian Brauner
2018-09-27 21:51 ` Jann Horn
2018-09-27 22:45 ` Kees Cook
2018-09-27 23:08 ` Tycho Andersen
2018-09-27 23:04 ` Tycho Andersen
2018-09-27 23:37 ` Jann Horn
2018-09-29 0:28 ` Aleksa Sarai
2018-09-27 15:11 ` [PATCH v7 2/6] seccomp: make get_nth_filter available outside of CHECKPOINT_RESTORE Tycho Andersen
2018-09-27 16:51 ` Jann Horn
2018-09-27 21:42 ` Kees Cook
2018-10-08 13:55 ` Christian Brauner
2018-09-27 15:11 ` [PATCH v7 3/6] seccomp: add a way to get a listener fd from ptrace Tycho Andersen
2018-09-27 16:20 ` Jann Horn
2018-09-27 16:34 ` Tycho Andersen
2018-09-27 17:35 ` Jann Horn
2018-09-27 18:09 ` Tycho Andersen
2018-09-27 21:53 ` Kees Cook
2018-10-08 15:16 ` Christian Brauner
2018-10-08 15:33 ` Jann Horn
2018-10-08 16:21 ` Christian Brauner
2018-10-08 16:42 ` Jann Horn
2018-10-08 18:18 ` Christian Brauner
2018-10-09 12:39 ` Jann Horn
2018-10-09 13:28 ` Christian Brauner
2018-10-09 13:36 ` Jann Horn
2018-10-09 13:49 ` Christian Brauner
2018-10-09 13:50 ` Jann Horn
2018-10-09 14:09 ` Christian Brauner
2018-10-09 15:26 ` Jann Horn
2018-10-09 16:20 ` Christian Brauner
2018-10-09 16:26 ` Jann Horn
2018-10-10 12:54 ` Christian Brauner
2018-10-10 13:09 ` Christian Brauner
2018-10-10 13:10 ` Jann Horn
2018-10-10 13:18 ` Christian Brauner
2018-10-10 15:31 ` Paul Moore
2018-10-10 15:33 ` Jann Horn
2018-10-10 15:39 ` Christian Brauner
2018-10-10 16:54 ` Tycho Andersen
2018-10-10 17:15 ` Christian Brauner
2018-10-10 17:26 ` Tycho Andersen
2018-10-10 18:28 ` Christian Brauner
2018-10-11 7:24 ` Paul Moore
2018-10-11 13:39 ` Jann Horn
2018-10-11 23:10 ` Paul Moore
2018-10-12 1:02 ` Andy Lutomirski
2018-10-12 20:02 ` Tycho Andersen
2018-10-12 20:06 ` Jann Horn
2018-10-12 20:11 ` Christian Brauner
2018-10-08 18:00 ` Tycho Andersen
2018-10-08 18:41 ` Christian Brauner
2018-10-10 17:45 ` Andy Lutomirski
2018-10-10 18:26 ` Christian Brauner
2018-09-27 15:11 ` [PATCH v7 4/6] files: add a replace_fd_files() function Tycho Andersen
2018-09-27 16:49 ` Jann Horn
2018-09-27 18:04 ` Tycho Andersen
2018-09-27 21:59 ` Kees Cook
2018-09-28 2:20 ` Kees Cook
2018-09-28 2:46 ` Jann Horn
2018-09-28 5:23 ` Tycho Andersen
2018-09-27 15:11 ` [PATCH v7 5/6] seccomp: add a way to pass FDs via a notification fd Tycho Andersen
2018-09-27 16:39 ` Jann Horn
2018-09-27 22:13 ` Tycho Andersen
2018-09-27 19:28 ` Jann Horn
2018-09-27 22:14 ` Tycho Andersen
2018-09-27 22:17 ` Jann Horn
2018-09-27 22:49 ` Tycho Andersen
2018-09-27 22:09 ` Kees Cook
2018-09-27 22:15 ` Tycho Andersen
2018-09-27 15:11 ` [PATCH v7 6/6] samples: add an example of seccomp user trap Tycho Andersen
2018-09-27 22:11 ` Kees Cook
2018-09-28 21:57 ` [PATCH v7 0/6] seccomp trap to userspace Michael Kerrisk (man-opages)
2018-09-28 22:03 ` Tycho Andersen
2018-09-28 22:16 ` Michael Kerrisk (man-pages)
2018-09-28 22:34 ` Kees Cook
2018-09-28 22:46 ` Michael Kerrisk (man-pages)
2018-09-28 22:48 ` Jann Horn
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