linux-kernel - Re: [syzbot] [usb-storage?] divide error in isd200_ata

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Date: Wed, 28 Feb 2024 17:20:29 +0100
From: Oliver Neukum <oneukum@...e.com>
To: Alan Stern <stern@...land.harvard.edu>, Oliver Neukum <oneukum@...e.com>
Cc: syzbot <syzbot+28748250ab47a8f04100@...kaller.appspotmail.com>,
 bvanassche@....org, emilne@...hat.com, gregkh@...uxfoundation.org,
 linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
 martin.petersen@...cle.com, syzkaller-bugs@...glegroups.com,
 tasos@...ossah.com, usb-storage@...ts.one-eyed-alien.net
Subject: Re: [syzbot] [usb-storage?] divide error in isd200_ata_command

On 26.02.24 19:13, Alan Stern wrote:

>> It oopses here:
>>
>> 		} else {
>> 			if (!id[ATA_ID_SECTORS] || !id[ATA_ID_HEADS])
>> 				goto too_early;
> 
> Those two lines are debugging code you added, right?

Yes, sorry about that.

> 
>> 			sectnum = (u8)((lba % id[ATA_ID_SECTORS]) + 1);
>> 			cylinder = (u16)(lba / (id[ATA_ID_SECTORS] *
>> 					id[ATA_ID_HEADS]));
>>
>> in isd200_scsi_to_ata() because it must not be called before isd200_get_inquiry_data()
>> has completed.
> 
> It can't be; isd200_get_inquiry_data is called by isd200_Initialization
> during probe before any SCSI commands are transmitted.

So, you are concluding that the bisection is spurious because
without that patch the SCSI layer would see a capacity of zero
and not even try to read anything?

	Regards
		Oliver