linux-kernel - Re: [PATCH] kernel/groups.c: consider about NULL for 'group

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Date:	Tue, 03 Sep 2013 13:23:20 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [PATCH] kernel/groups.c: consider about NULL for 'group_info'
 in all related extern functions

Hello Maintainers:

Please help check this patch, when you have time.

If need a related test, please let me know, I should try (better to
provide some suggestions for test).


Thanks.

On 08/20/2013 11:03 AM, Chen Gang wrote:
> 
> If this patch is correct, also need modify the man page for the return
> value of getgroups().
> 
> Thanks.
> 
> On 08/20/2013 11:01 AM, Chen Gang wrote:
>> groups_alloc() can return NULL for 'group_info', also group_search()
>> already considers about NULL for 'group_info', so can assume the caller
>> has right to use all related extern functions when 'group_info' is NULL.
>>
>> For groups_free(), need check NULL to match groups_alloc(), just like
>> kmalloc/free().
>>
>> For set_groups(), can allow the caller to set NULL parameter to new
>> 'cred'.
>>
>> For system call getgroups(), if 'cred->group_info' is NULL, need return
>> the related error code (no related data), also need change the related
>> man page ("man 2 getgroups") to complete the return value.
>>
>>
>> Signed-off-by: Chen Gang <gang.chen@...anux.com>
>> ---
>>  kernel/groups.c |   14 +++++++++++---
>>  1 files changed, 11 insertions(+), 3 deletions(-)
>>
>> diff --git a/kernel/groups.c b/kernel/groups.c
>> index 6b2588d..a21a4ce 100644
>> --- a/kernel/groups.c
>> +++ b/kernel/groups.c
>> @@ -52,6 +52,9 @@ EXPORT_SYMBOL(groups_alloc);
>>
>>  void groups_free(struct group_info *group_info)
>>  {
>> +	if (!group_info)
>> +		return;
>> +
>>  	if (group_info->blocks[0] != group_info->small_block) {
>>  		int i;
>>  		for (i = 0; i < group_info->nblocks; i++)
>> @@ -163,9 +166,12 @@ int groups_search(const struct group_info
>> *group_info, kgid_t grp)
>>   */
>>  int set_groups(struct cred *new, struct group_info *group_info)
>>  {
>> -	put_group_info(new->group_info);
>> -	groups_sort(group_info);
>> -	get_group_info(group_info);
>> +	if (new->group_info)
>> +		put_group_info(new->group_info);
>> +	if (group_info) {
>> +		groups_sort(group_info);
>> +		get_group_info(group_info);
>> +	}
>>  	new->group_info = group_info;
>>  	return 0;
>>  }
>> @@ -206,6 +212,8 @@ SYSCALL_DEFINE2(getgroups, int, gidsetsize, gid_t
>> __user *, grouplist)
>>
>>  	if (gidsetsize < 0)
>>  		return -EINVAL;
>> +	if (!cred->group_info)
>> +		return -ENODATA;
>>
>>  	/* no need to grab task_lock here; it cannot change */
>>  	i = cred->group_info->ngroups;
>>
> 
> 


-- 
Chen Gang
--
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