Re: [RFC PATCH 1/2] autofs: set compat flag on sbi when daemon uses 32bit addressation

[Ian Kent]

On 14/09/17 19:39, Stanislav Kinsburskiy wrote:
> 
> 
> 14.09.2017 13:29, Ian Kent ÐÐÑÐÑ:
>> On 14/09/17 17:24, Stanislav Kinsburskiy wrote:
>>>
>>>
>>> 14.09.2017 02:38, Ian Kent ÐÐÑÐÑ:
>>>> On 01/09/17 19:21, Stanislav Kinsburskiy wrote:
>>>>> Signed-off-by: Stanislav Kinsburskiy <skinsbursky@xxxxxxxxxxxxx>
>>>>> ---
>>>>>  fs/autofs4/autofs_i.h  |    3 +++
>>>>>  fs/autofs4/dev-ioctl.c |    3 +++
>>>>>  fs/autofs4/inode.c     |    4 +++-
>>>>>  3 files changed, 9 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h
>>>>> index 4737615..3da105f 100644
>>>>> --- a/fs/autofs4/autofs_i.h
>>>>> +++ b/fs/autofs4/autofs_i.h
>>>>> @@ -120,6 +120,9 @@ struct autofs_sb_info {
>>>>>  	struct list_head active_list;
>>>>>  	struct list_head expiring_list;
>>>>>  	struct rcu_head rcu;
>>>>> +#ifdef CONFIG_COMPAT
>>>>> +	unsigned is32bit:1;
>>>>> +#endif
>>>>>  };
>>>>>  
>>>>>  static inline struct autofs_sb_info *autofs4_sbi(struct super_block *sb)
>>>>> diff --git a/fs/autofs4/dev-ioctl.c b/fs/autofs4/dev-ioctl.c
>>>>> index b7c816f..467d6c4 100644
>>>>> --- a/fs/autofs4/dev-ioctl.c
>>>>> +++ b/fs/autofs4/dev-ioctl.c
>>>>> @@ -397,6 +397,9 @@ static int autofs_dev_ioctl_setpipefd(struct file *fp,
>>>>>  		sbi->pipefd = pipefd;
>>>>>  		sbi->pipe = pipe;
>>>>>  		sbi->catatonic = 0;
>>>>> +#ifdef CONFIG_COMPAT
>>>>> +		sbi->is32bit = is_compat_task();
>>>>> +#endif
>>>>>  	}
>>>>>  out:
>>>>>  	put_pid(new_pid);
>>>>> diff --git a/fs/autofs4/inode.c b/fs/autofs4/inode.c
>>>>> index 09e7d68..21d3c0b 100644
>>>>> --- a/fs/autofs4/inode.c
>>>>> +++ b/fs/autofs4/inode.c
>>>>> @@ -301,7 +301,9 @@ int autofs4_fill_super(struct super_block *s, void *data, int silent)
>>>>>  	} else {
>>>>>  		sbi->oz_pgrp = get_task_pid(current, PIDTYPE_PGID);
>>>>>  	}
>>>>> -
>>>>> +#ifdef CONFIG_COMPAT
>>>>> +	sbi->is32bit = is_compat_task();
>>>>> +#endif
>>>>>  	if (autofs_type_trigger(sbi->type))
>>>>>  		__managed_dentry_set_managed(root);
>>>>>  
>>>>>
>>>>
>>>> Not sure about this.
>>>>
>>>> Don't you think it would be better to avoid the in code #ifdefs by doing some
>>>> checks and defines in the header file and defining what's need to just use
>>>> is_compat_task().
>>>>
>>>
>>> Yes, might be...
>>>
>>>> Not sure 2 patches are needed for this either ......
>>>>
>>>
>>> Well, I found this issue occasionally.
>>
>> I'm wondering what the symptoms are?
>>
> 
> Size of struct autofs_v5_packet is 300 bytes for x86 and 304 bytes for x86_64.
> Which means, that 32bit task can read more than size of autofs_v5_packet on 64bit kernel.

Are you sure?

Shouldn't that be a short read on the x86 side of a 4 bytes longer
structure on the x86_64 side.

I didn't think you could have a 64 bit client on a 32 bit kernel
so the converse (the read past end of struct) doesn't apply.

Ian