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.
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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