linux-kernel - Re: general protection fault in del

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Date:   Mon, 1 Nov 2021 13:01:42 -0700
From:   Tadeusz Struk <tadeusz.struk@...aro.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: general protection fault in del_gendisk

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?

-- 
Thanks,
Tadeusz