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SubjectRe: [RFC PATCH 1/2] autofs: set compat flag on sbi when daemon uses 32bit addressation
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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@virtuozzo.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
>

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