linux-kernel - Re: general protection fault in del

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Date:   Mon, 1 Nov 2021 14:03:58 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Tadeusz Struk <tadeusz.struk@...aro.org>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: general protection fault in del_gendisk

On 11/1/21 2:01 PM, Tadeusz Struk wrote:
> On 10/29/21 12:13, Tadeusz Struk wrote:
>> Hi,
>> I'm looking at a bug found by the syzkaller robot [1], and I just wanted
>> to confirm that my understanding is correct, and the issue can be closed.
>> First, the kernel is configured with some fault injections enabled:
>>
>> CONFIG_FAULT_INJECTION=y
>> CONFIG_FAILSLAB=y
>> CONFIG_FAIL_PAGE_ALLOC=y
>>
>> The test adds loop devices, which causes some entries in sysfs to be created.
>> It does some magic with ioctls, which calls:
>> __device_add_disk() -> register_disk()
>> which eventually triggers sysfs_create_files() and it crashes there,
>> in line 627 [2], because the fault injector logic triggers it.
>> That can be seen in the trace [3]:
>> [   34.089707][ T1813] FAULT_INJECTION: forcing a failure.
>>
>> Sysfs code returns a -ENOMEM error, but because the __device_add_disk()
>> implementation mostly uses void function, and doesn't return on errors [4]
>> it goes farther, hits some warnings, like:
>> disk_add_events() -> sysfs_create_files() -> sysfs_create_file_ns() - > WARN()
>> and eventually triggers general protection fault in sysfs code, and panics there.
>>
>> I think for this to recover and return an error to the caller via ioctl()
>> the __device_add_disk() code would need be reworked to handle errors,
>> and return errors to the caller.
>> My question is: is it implemented like this by design? Are there any plans
>> to make it fail more gracefully?
> 
> Hi,
> Any comments on this one?

People will take a look at it, but you sent it out on a Saturday right
before a merge window, doing a 'ping' kind of followup on a Monday is
way too soon.

-- 
Jens Axboe