On 09/04/2013 05:42 PM, Alan Stern wrote:
> On Wed, 4 Sep 2013, Paolo Bonzini wrote:
>
>>> --- usb-3.11.orig/drivers/scsi/sd.c
>>> +++ usb-3.11/drivers/scsi/sd.c
>>> @@ -2419,7 +2419,7 @@ sd_read_cache_type(struct scsi_disk *sdk
>>> }
>>> }
>>>
>>> - if (modepage == 0x3F) {
>>> + if (modepage == 0x3F || offset + 2 >= len) {
>>> sd_printk(KERN_ERR, sdkp, "No Caching mode page "
>>> "present\n");
>>> goto defaults;
>>
>> If you do this, the buggy "if" becomes dead code (the loop above doesn't
>> have any "break", so you know that offset >= len and the new condition
>> is always true).
>>
>> So the patch does indeed prevent the bug, but the code can be simplified.
>
> That's right. I didn't realize it at first, but the only way to get
> here is if the next page offset lies beyond the end of the data in the
> buffer. Therefore the patch can be simplified as follows.
>
Oh, pretty please. I already had customers complaining about the
'got wrong page' message. Which again demonstrated nicely the
uncertainty relation between correctness and usability :-)
> Alan Stern
>
>
>
> Index: usb-3.11/drivers/scsi/sd.c
> ===================================================================
> --- usb-3.11.orig/drivers/scsi/sd.c
> +++ usb-3.11/drivers/scsi/sd.c
> @@ -2419,14 +2419,9 @@ sd_read_cache_type(struct scsi_disk *sdk
> }
> }
>
> - if (modepage == 0x3F) {
> - sd_printk(KERN_ERR, sdkp, "No Caching mode page "
> - "present\n");
> - goto defaults;
> - } else if ((buffer[offset] & 0x3f) != modepage) {
> - sd_printk(KERN_ERR, sdkp, "Got wrong page\n");
> - goto defaults;
> - }
> + sd_printk(KERN_ERR, sdkp, "No Caching mode page found\n");
> + goto defaults;
> +
> Page_found:
> if (modepage == 8) {
> sdkp->WCE = ((buffer[offset + 2] & 0x04) != 0);
>
> --
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>
Acked-by: Hannes Reinecke <hare@xxxxxxx>
Cheers,
Hannes
--
Dr. Hannes Reinecke zSeries & Storage
hare@xxxxxxx +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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