Re: [PATCH 1/8] apparmor: just use vfs_kern_mount to make .null

On 4/16/20 8:44 AM, Luis Chamberlain wrote:
> On Tue, Apr 14, 2020 at 02:42:55PM +0200, Emanuele Giuseppe Esposito wrote:
>> aa_mk_null_file is using simple_pin_fs/simple_release_fs with local
>> variables as arguments, for what would amount to a simple
>> vfs_kern_mount/mntput pair if everything was inlined.  Just use
>> the normal filesystem API since the reference counting is not needed
>> here.
> 
> *Why* is refcounting not needed here?

The refcount is a local variable and is always 0 on entry and exit, so 
it is not necessary to have refcounting across function invocations, 
such as what simple_pin_fs and simple_release_fs provide.

Thank you,

Emanuele
> 
>     Luis
> 
>>
>> Signed-off-by: Emanuele Giuseppe Esposito <[email protected]>
>> ---
>>   security/apparmor/apparmorfs.c | 12 ++++++------
>>   1 file changed, 6 insertions(+), 6 deletions(-)
>>
>> diff --git a/security/apparmor/apparmorfs.c b/security/apparmor/apparmorfs.c
>> index 280741fc0f5f..828bb1eb77ea 100644
>> --- a/security/apparmor/apparmorfs.c
>> +++ b/security/apparmor/apparmorfs.c
>> @@ -2525,14 +2525,14 @@ struct path aa_null;
>>   
>>   static int aa_mk_null_file(struct dentry *parent)
>>   {
>> -	struct vfsmount *mount = NULL;
>> +	struct file_system_type *type = parent->d_sb->s_type;
>> +	struct vfsmount *mount;
>>   	struct dentry *dentry;
>>   	struct inode *inode;
>> -	int count = 0;
>> -	int error = simple_pin_fs(parent->d_sb->s_type, &mount, &count);
>>   
>> -	if (error)
>> -		return error;
>> +	mount = vfs_kern_mount(type, SB_KERNMOUNT, type->name, NULL);
>> +	if (IS_ERR(mount))
>> +		return PTR_ERR(mount);
>>   
>>   	inode_lock(d_inode(parent));
>>   	dentry = lookup_one_len(NULL_FILE_NAME, parent, strlen(NULL_FILE_NAME));
>> @@ -2561,7 +2561,7 @@ static int aa_mk_null_file(struct dentry *parent)
>>   	dput(dentry);
>>   out:
>>   	inode_unlock(d_inode(parent));
>> -	simple_release_fs(&mount, &count);
>> +	mntput(mount);
>>   	return error;
>>   }
>>   
>> -- 
>> 2.25.2
>>
>