Re: [PATCH 1/2 v3] user namespace: use union in {g,u}idmap struct

From: Eric W. Biederman
Date: Wed Oct 18 2017 - 20:48:53 EST

Christian Brauner <christian.brauner@xxxxxxxxxxxxx> writes:

> I'm not sure why the build is complaining about how the union is initialized
> here. This looks legitimate to me and I can't reproduce this locally with or
> without the appended config. The struct introduced here is:
>
> #define UID_GID_MAP_MAX_EXTENTS 5
>
> struct uid_gid_extent {
> u32 first;
> u32 lower_first;
> u32 count;
> };
>
> struct uid_gid_map { /* 64 bytes -- 1 cache line */
> u32 nr_extents;
> union {
> struct uid_gid_extent extent[UID_GID_MAP_MAX_EXTENTS];
> struct {
> struct uid_gid_extent *forward;
> struct uid_gid_extent *reverse;
> };
> };
> };
>
> And the initialization in kernel/user.c which I didn't change looks correct.
> But maybe I'm missing the point.

You may want to check your compiler version this feels like a compiler
dependent error.

It looks like gcc isn't happy about not having braces for the anonymous
union of extent and the anonymouns structure that holds forward and
reverse.

FYI since I am commenting. I took a quick skim through your code today
and at first glance everything looks good. The performance is nice and
fast, and the changes look reasonable at first glance.

I think there are some nits that can be picked but nothing yet that
indicates the code is working incorrectly.

Eric

> On Thu, Oct 19, 2017 at 06:51:48AM +0800, kbuild test robot wrote:
>> Hi Christian,
>>
>> [auto build test ERROR on linus/master]
>> [also build test ERROR on v4.14-rc5 next-20171017]
>> [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
>>
>> url: https://github.com/0day-ci/linux/commits/Christian-Brauner/user-namespace-use-union-in-g-u-idmap-struct/20171019-022142
>> config: x86_64-randconfig-a0-10190527 (attached as .config)
>> compiler: gcc-4.4 (Debian 4.4.7-8) 4.4.7
>> reproduce:
>> # save the attached .config to linux build tree
>> make ARCH=x86_64
>>
>> All error/warnings (new ones prefixed by >>):
>>
>> >> kernel/user.c:29: error: unknown field 'extent' specified in initializer
>> >> kernel/user.c:30: error: unknown field 'first' specified in initializer
>> >> kernel/user.c:30: warning: missing braces around initializer
>> kernel/user.c:30: warning: (near initialization for 'init_user_ns.uid_map.<anonymous>.extent')
>> >> kernel/user.c:31: error: unknown field 'lower_first' specified in initializer
>> >> kernel/user.c:31: warning: excess elements in union initializer
>> kernel/user.c:31: warning: (near initialization for 'init_user_ns.uid_map.<anonymous>')
>> >> kernel/user.c:32: error: unknown field 'count' specified in initializer
>> kernel/user.c:32: warning: excess elements in union initializer
>> kernel/user.c:32: warning: (near initialization for 'init_user_ns.uid_map.<anonymous>')
>> kernel/user.c:37: error: unknown field 'extent' specified in initializer
>> kernel/user.c:38: error: unknown field 'first' specified in initializer
>> kernel/user.c:39: error: unknown field 'lower_first' specified in initializer
>> kernel/user.c:39: warning: excess elements in union initializer
>> kernel/user.c:39: warning: (near initialization for 'init_user_ns.gid_map.<anonymous>')
>> kernel/user.c:40: error: unknown field 'count' specified in initializer
>> kernel/user.c:40: warning: excess elements in union initializer
>> kernel/user.c:40: warning: (near initialization for 'init_user_ns.gid_map.<anonymous>')
>> kernel/user.c:45: error: unknown field 'extent' specified in initializer
>> kernel/user.c:46: error: unknown field 'first' specified in initializer
>> kernel/user.c:47: error: unknown field 'lower_first' specified in initializer
>> kernel/user.c:47: warning: excess elements in union initializer
>> kernel/user.c:47: warning: (near initialization for 'init_user_ns.projid_map.<anonymous>')
>> kernel/user.c:48: error: unknown field 'count' specified in initializer
>> kernel/user.c:48: warning: excess elements in union initializer
>> kernel/user.c:48: warning: (near initialization for 'init_user_ns.projid_map.<anonymous>')
>>
>> vim +/lower_first +31 kernel/user.c
>>
>> ^1da177e4 Linus Torvalds 2005-04-16 21
>> 59607db36 Serge E. Hallyn 2011-03-23 22 /*
>> 59607db36 Serge E. Hallyn 2011-03-23 23 * userns count is 1 for root user, 1 for init_uts_ns,
>> 59607db36 Serge E. Hallyn 2011-03-23 24 * and 1 for... ?
>> 59607db36 Serge E. Hallyn 2011-03-23 25 */
>> aee16ce73 Pavel Emelyanov 2008-02-08 26 struct user_namespace init_user_ns = {
>> 22d917d80 Eric W. Biederman 2011-11-17 27 .uid_map = {
>> 22d917d80 Eric W. Biederman 2011-11-17 28 .nr_extents = 1,
>> 22d917d80 Eric W. Biederman 2011-11-17 @29 .extent[0] = {
>> 22d917d80 Eric W. Biederman 2011-11-17 @30 .first = 0,
>> 22d917d80 Eric W. Biederman 2011-11-17 @31 .lower_first = 0,
>> 4b06a81f1 Eric W. Biederman 2012-05-19 @32 .count = 4294967295U,
>> 22d917d80 Eric W. Biederman 2011-11-17 33 },
>> 22d917d80 Eric W. Biederman 2011-11-17 34 },
>> 22d917d80 Eric W. Biederman 2011-11-17 35 .gid_map = {
>> 22d917d80 Eric W. Biederman 2011-11-17 36 .nr_extents = 1,
>> 22d917d80 Eric W. Biederman 2011-11-17 37 .extent[0] = {
>> 22d917d80 Eric W. Biederman 2011-11-17 38 .first = 0,
>> 22d917d80 Eric W. Biederman 2011-11-17 39 .lower_first = 0,
>> 4b06a81f1 Eric W. Biederman 2012-05-19 40 .count = 4294967295U,
>> 22d917d80 Eric W. Biederman 2011-11-17 41 },
>> 22d917d80 Eric W. Biederman 2011-11-17 42 },
>> f76d207a6 Eric W. Biederman 2012-08-30 43 .projid_map = {
>> f76d207a6 Eric W. Biederman 2012-08-30 44 .nr_extents = 1,
>> f76d207a6 Eric W. Biederman 2012-08-30 45 .extent[0] = {
>> f76d207a6 Eric W. Biederman 2012-08-30 46 .first = 0,
>> f76d207a6 Eric W. Biederman 2012-08-30 47 .lower_first = 0,
>> f76d207a6 Eric W. Biederman 2012-08-30 48 .count = 4294967295U,
>> f76d207a6 Eric W. Biederman 2012-08-30 49 },
>> f76d207a6 Eric W. Biederman 2012-08-30 50 },
>> c61a2810a Eric W. Biederman 2012-12-28 51 .count = ATOMIC_INIT(3),
>> 783291e69 Eric W. Biederman 2011-11-17 52 .owner = GLOBAL_ROOT_UID,
>> 783291e69 Eric W. Biederman 2011-11-17 53 .group = GLOBAL_ROOT_GID,
>> 435d5f4bb Al Viro 2014-10-31 54 .ns.inum = PROC_USER_INIT_INO,
>> 33c429405 Al Viro 2014-11-01 55 #ifdef CONFIG_USER_NS
>> 33c429405 Al Viro 2014-11-01 56 .ns.ops = &userns_operations,
>> 33c429405 Al Viro 2014-11-01 57 #endif
>> 9cc46516d Eric W. Biederman 2014-12-02 58 .flags = USERNS_INIT_FLAGS,
>> 6bd364d82 Xiao Guangrong 2013-12-13 59 #ifdef CONFIG_PERSISTENT_KEYRINGS
>> 6bd364d82 Xiao Guangrong 2013-12-13 60 .persistent_keyring_register_sem =
>> 6bd364d82 Xiao Guangrong 2013-12-13 61 __RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem),
>> f36f8c75a David Howells 2013-09-24 62 #endif
>> aee16ce73 Pavel Emelyanov 2008-02-08 63 };
>> aee16ce73 Pavel Emelyanov 2008-02-08 64 EXPORT_SYMBOL_GPL(init_user_ns);
>> aee16ce73 Pavel Emelyanov 2008-02-08 65
>>
>> :::::: The code at line 31 was first introduced by commit
>> :::::: 22d917d80e842829d0ca0a561967d728eb1d6303 userns: Rework the user_namespace adding uid/gid mapping support
>>
>> :::::: TO: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
>> :::::: CC: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
>>
>> ---
>> 0-DAY kernel test infrastructure Open Source Technology Center
>> https://lists.01.org/pipermail/kbuild-all Intel Corporation