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Groups > linux.kernel > #1449053
| From | ebiederm@xmission.com (Eric W. Biederman) |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH 1/5] namespaces: move user_ns into ns_common |
| Date | 2016-07-24 07:20 +0200 |
| Message-ID | <rYjZv-3Nk-3@gated-at.bofh.it> (permalink) |
| References | <rUWZs-6XY-11@gated-at.bofh.it> <rV0Tn-ZV-5@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
Andrey Vagin <avagin@openvz.org> writes:
> Every namespace has a pointer to an user namespace where is was created,
> but they're all privately embedded in the individual namespace specific
> structures.
>
> Now we are going to add an user-space interface to get an owning user
> namespace, so it looks reasonable to move it into ns_common.
>
> Originally this idea was suggested by James Bottomley.
I skimmed through this and I really don't like move user_ns into
ns_common. If for no other reason that it seems to have guarantteed
this patchset as written would not apply to my tree.
> diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
> index 8297e5b..a941b44 100644
> --- a/include/linux/user_namespace.h
> +++ b/include/linux/user_namespace.h
> @@ -27,11 +27,15 @@ struct user_namespace {
> struct uid_gid_map gid_map;
> struct uid_gid_map projid_map;
> atomic_t count;
> - struct user_namespace *parent;
> int level;
> kuid_t owner;
> kgid_t group;
> - struct ns_common ns;
> +
> + /* ->ns.user_ns and ->parent are synonyms */
> + union {
> + struct user_namespace *parent;
> + struct ns_common ns;
> + };
> unsigned long flags;
>
> /* Register of per-UID persistent keyrings for this namespace */
This union is unmaintainable. It is very easy for someone to change
ns_common and accidentially break this. The C standard does not
allow data to be accessed as either one union member or the other.
Which means semantically this code relies on undefined behavior, and
the compiler can do anything in this case and gcc has sometimes been
known to use that allowance.
Eric
Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
[PATCH 0/5 RFC] Add an interface to discover relationships between namespaces Andrey Vagin <avagin@openvz.org> - 2016-07-14 20:30 +0200
[PATCH 2/5] kernel: add a helper to get an owning user namespace for a namespace Andrey Vagin <avagin@openvz.org> - 2016-07-14 20:30 +0200
Re: [PATCH 2/5] kernel: add a helper to get an owning user namespace for a namespace "W. Trevor King" <wking@tremily.us> - 2016-07-14 21:10 +0200
Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces Andrey Vagin <avagin@openvz.org> - 2016-07-15 00:10 +0200
[PATCH 5/5] tools/testing: add a test to check nsfs ioctl-s Andrey Vagin <avagin@openvz.org> - 2016-07-15 04:20 +0200
[PATCH 4/5] nsfs: add ioctl to get a parent namespace Andrey Vagin <avagin@openvz.org> - 2016-07-15 04:20 +0200
Re: [PATCH 4/5] nsfs: add ioctl to get a parent namespace ebiederm@xmission.com (Eric W. Biederman) - 2016-07-24 07:30 +0200
[PATCH 3/5] nsfs: add ioctl to get an owning user namespace for ns file descriptor Andrey Vagin <avagin@openvz.org> - 2016-07-15 04:20 +0200
[PATCH 2/5] kernel: add a helper to get an owning user namespace for a namespace Andrey Vagin <avagin@openvz.org> - 2016-07-15 04:20 +0200
Re: [PATCH 2/5] kernel: add a helper to get an owning user namespace for a namespace ebiederm@xmission.com (Eric W. Biederman) - 2016-07-24 07:20 +0200
Re: [PATCH 2/5] kernel: add a helper to get an owning user namespace for a namespace ebiederm@xmission.com (Eric W. Biederman) - 2016-07-24 16:50 +0200
Re: [PATCH 2/5] kernel: add a helper to get an owning user namespace for a namespace "W. Trevor King" <wking@tremily.us> - 2016-07-24 19:10 +0200
Re: [PATCH 2/5] kernel: add a helper to get an owning user namespace for a namespace "W. Trevor King" <wking@tremily.us> - 2016-07-24 19:00 +0200
Re: [PATCH 1/5] namespaces: move user_ns into ns_common ebiederm@xmission.com (Eric W. Biederman) - 2016-07-24 07:20 +0200
Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces ebiederm@xmission.com (Eric W. Biederman) - 2016-07-24 07:30 +0200
Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-07-21 16:50 +0200
Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces Andrey Vagin <avagin@openvz.org> - 2016-07-22 20:30 +0200
Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-07-25 13:50 +0200
Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces ebiederm@xmission.com (Eric W. Biederman) - 2016-07-25 15:40 +0200
Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-07-25 16:50 +0200
Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces "Serge E. Hallyn" <serge@hallyn.com> - 2016-07-25 17:00 +0200
Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces ebiederm@xmission.com (Eric W. Biederman) - 2016-07-25 17:40 +0200
Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces ebiederm@xmission.com (Eric W. Biederman) - 2016-07-25 17:20 +0200
Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces "W. Trevor King" <wking@tremily.us> - 2016-07-23 23:20 +0200
Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces James Bottomley <James.Bottomley@HansenPartnership.com> - 2016-07-23 23:40 +0200
Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces "W. Trevor King" <wking@tremily.us> - 2016-07-24 00:10 +0200
Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces ebiederm@xmission.com (Eric W. Biederman) - 2016-07-24 00:20 +0200
Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces "W. Trevor King" <wking@tremily.us> - 2016-07-24 00:40 +0200
Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces ebiederm@xmission.com (Eric W. Biederman) - 2016-07-24 07:10 +0200
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