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

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Date:   Thu, 14 Sep 2017 13:39:21 +0200
From:   Stanislav Kinsburskiy <skinsbursky@...tuozzo.com>
To:     Ian Kent <raven@...maw.net>
Cc:     autofs@...r.kernel.org, linux-kernel@...r.kernel.org,
        devel@...nvz.org, ldv@...linux.org
Subject: Re: [RFC PATCH 1/2] autofs: set compat flag on sbi when daemon uses
 32bit addressation



14.09.2017 13:29, Ian Kent пишет:
> On 14/09/17 17:24, Stanislav Kinsburskiy wrote:
>>
>>
>> 14.09.2017 02:38, Ian Kent пишет:
>>> On 01/09/17 19:21, Stanislav Kinsburskiy wrote:
>>>> Signed-off-by: Stanislav Kinsburskiy <skinsbursky@...tuozzo.com>
>>>> ---
>>>>  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.

>> And, frankly speaking, it's not clear to me, whether this issue is important at all, so I wanted to clarify this first.
>> Thanks to O_DIRECT, the only way to catch the issue is to try to read more, than expected, in compat task (that's how I found it).
> 
> Right, the O_DIRECT patch from Linus was expected to fix the structure
> alignment problem. The stuct field offsets are ok aren't they?
> 

Yes, they are ok.

>> I don't see any other flaw so far. And if so, that, probably, we shouldn't care about the issue at all.
>> What do you think?
> 
> If we are seeing hangs, incorrect struct fields or similar something
> should be done about it but if all is actually working ok then the
> O_DIRECT fix is doing it's job and further changes aren't necessary.
> 

Well, yes. O_DIRECT fix covers the issue.
Ok then.
Thanks for the clarification!

> Ian
>