Re: [PATCH] loop: remember whether sysfs_create_group() succeeded

[Jens Axboe <axboe@kernel.dk>]

On 5/4/18 8:40 AM, Tetsuo Handa wrote:
> Jens Axboe wrote:
>> On 5/4/18 8:27 AM, Tetsuo Handa wrote:
>>> Jens Axboe wrote:
>>>> On 5/4/18 5:47 AM, Tetsuo Handa wrote:
>>>>> >From 626d33de1b70b11ecaf95a9f83f7644998e54cbb Mon Sep 17 00:00:00 2001
>>>>> From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
>>>>> Date: Wed, 2 May 2018 23:03:48 +0900
>>>>> Subject: [PATCH] loop: remember whether sysfs_create_group() succeeded
>>>>>
>>>>> syzbot is hitting WARN() triggered by memory allocation fault
>>>>> injection [1] because loop module is calling sysfs_remove_group()
>>>>> when sysfs_create_group() failed.
>>>>> Fix this by remembering whether sysfs_create_group() succeeded.
>>>>
>>>> Can we store this locally instead of in the loop_device? Also,
>>>> naming wise, something like sysfs_init_done would be more readily
>>>> understandable.
>>>
>>> Whether sysfs entry for this loop device exists is per "struct loop_device"
>>> flag, isn't it? What does "locally" mean?
>>
>> I'm assuming this is calling remove in an error path when alloc fails.
>> So it should be possible to know locally whether this was done or not,
>> before calling the teardown. Storing this is in the loop_device seems
>> like a bit of a hack.
> 
> The loop module ignores sysfs_create_group() failure and pretends that
> LOOP_SET_FD request succeeded. I guess that the author of commit
> ee86273062cbb310 ("loop: add some basic read-only sysfs attributes")
> assumed that it is not a fatal error enough to abort LOOP_SET_FD request.
> 
> Do we want to abort LOOP_SET_FD request if sysfs_create_group() failed?

Probably safer to retain that behavior.

>> If that's not easily done, then my next suggestion would be to
>> use a loop flag for it, LO_FLAGS_SYSFS_SETUP or something like that.
> 
> Yes, that would be possible.

Let's make that change.

-- 
Jens Axboe