[PATCH 5/5] block/scsi: correctly emulate the VPD block limits page

[Maxim Levitsky]

When the device doesn't support the VPD block limits page, we emulate it even
for SCSI passthrough.

As a part of the emulation we need to add it to the 'Supported VPD Pages'

The code that does this adds it to the page, but it doesn't increase the length
of the data to be copied to the guest, thus the guest never sees the VPD block
limits page as supported.

Bump the transfer size by 1 in this case.

I also refactored the code a bit, and I hopefully didn't introduce
another buffer overflow to this code...

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
 hw/scsi/scsi-generic.c | 28 +++++++++++++++++-----------
 1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c
index 6df67bf889..387d885aee 100644
--- a/hw/scsi/scsi-generic.c
+++ b/hw/scsi/scsi-generic.c
@@ -134,9 +134,9 @@ static int execute_command(BlockBackend *blk,
     return 0;
 }
 
-static void scsi_handle_inquiry_reply(SCSIGenericReq *r, SCSIDevice *s)
+static int scsi_handle_inquiry_reply(SCSIGenericReq *r, SCSIDevice *s, int len)
 {
-    uint8_t page, page_idx;
+    uint8_t page;
 
     /*
      *  EVPD set to zero returns the standard INQUIRY data.
@@ -188,20 +188,26 @@ static void scsi_handle_inquiry_reply(SCSIGenericReq *r, 
SCSIDevice *s)
              * right place with an in-place insert.  When the while loop
              * begins the device response is at r[0] to r[page_idx - 1].
              */
-            page_idx = lduw_be_p(r->buf + 2) + 4;
-            page_idx = MIN(page_idx, r->buflen);
+            uint16_t page_len = lduw_be_p(r->buf + 2) + 4;
+
+            /* pointer to first byte after the page that device gave us */
+            uint16_t page_idx = page_len;
+
+            if (page_idx >= r->buflen)
+                return len;
+
             while (page_idx > 4 && r->buf[page_idx - 1] >= 0xb0) {
-                if (page_idx < r->buflen) {
-                    r->buf[page_idx] = r->buf[page_idx - 1];
-                }
+                r->buf[page_idx] = r->buf[page_idx - 1];
                 page_idx--;
             }
-            if (page_idx < r->buflen) {
-                r->buf[page_idx] = 0xb0;
-            }
+            r->buf[page_idx] = 0xb0;
+
+            /* increase the page len field */
             stw_be_p(r->buf + 2, lduw_be_p(r->buf + 2) + 1);
+            len++;
         }
     }
+    return len;
 }
 
 static int scsi_generic_emulate_block_limits(SCSIGenericReq *r, SCSIDevice *s)
@@ -316,7 +322,7 @@ static void scsi_read_complete(void * opaque, int ret)
         }
     }
     if (r->req.cmd.buf[0] == INQUIRY) {
-        scsi_handle_inquiry_reply(r, s);
+        len = scsi_handle_inquiry_reply(r, s, len);
     }
 
 req_complete:
-- 
2.26.2