linux-kernel - Re: [PATCH 1/2 v4] user namespace: use union in {g,u}idmap struct

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Date:   Mon, 23 Oct 2017 09:45:34 +0300
From:   Nikolay Borisov <nborisov@...e.com>
To:     Christian Brauner <christian.brauner@...ntu.com>,
        ebiederm@...ssion.com, linux-kernel@...r.kernel.org
Cc:     serge@...lyn.com, stgraber@...ntu.com, tycho@...ho.ws
Subject: Re: [PATCH 1/2 v4] user namespace: use union in {g,u}idmap struct



On 23.10.2017 09:39, Nikolay Borisov wrote:
> 
> 
> On 19.10.2017 22:11, Christian Brauner wrote:
>> - Add a struct containing two pointer to extents and wrap both the static extent
>>   array and the struct into a union. This is done in preparation for bumping the
>>   {g,u}idmap limits for user namespaces.
>> - Add brackets around anonymous union when using designated initializers to
>>   initialize members in order to please gcc <= 4.4.
>>
>> Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
>> ---
>> Changelog 2017-10-19:
>> * kernel/user.c: Use brackets around anonymous union when using designated
>>   initializers to initialize members. This is done to please gcc <= 4.4.
>> ---
>>  include/linux/user_namespace.h | 18 +++++++++++++-----
>>  kernel/user.c                  | 30 ++++++++++++++++++------------
>>  2 files changed, 31 insertions(+), 17 deletions(-)
>>
>> diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
>> index c18e01252346..7c83d7f6289b 100644
>> --- a/include/linux/user_namespace.h
>> +++ b/include/linux/user_namespace.h
>> @@ -12,13 +12,21 @@
>>  
>>  #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;
>> -	struct uid_gid_extent {
>> -		u32 first;
>> -		u32 lower_first;
>> -		u32 count;
>> -	} extent[UID_GID_MAP_MAX_EXTENTS];
>> +	union {
>> +		struct uid_gid_extent extent[UID_GID_MAP_MAX_EXTENTS];
>> +		struct {
>> +			struct uid_gid_extent *forward;
>> +			struct uid_gid_extent *reverse;
>> +		};
>> +	};
>>  };
>>  
>>  #define USERNS_SETGROUPS_ALLOWED 1UL
>> diff --git a/kernel/user.c b/kernel/user.c
>> index 00281add65b2..9a20acce460d 100644
>> --- a/kernel/user.c
>> +++ b/kernel/user.c
>> @@ -26,26 +26,32 @@
>>  struct user_namespace init_user_ns = {
>>  	.uid_map = {
>>  		.nr_extents = 1,
>> -		.extent[0] = {
>> -			.first = 0,
>> -			.lower_first = 0,
>> -			.count = 4294967295U,
>> +		{
>> +			.extent[0] = {
>> +				.first = 0,
>> +				.lower_first = 0,
>> +				.count = 4294967295U,
> 
> nit: ULONG_MAX ?

Well, actually UINT_MAX