[Qemu-devel] [PATCH 22/22] scsi: Guard against buflen exceeding req->cmd.xfer in scsi_disk_emulate_command

[Kevin Wolf <kwolf@redhat.com>]

From: Thomas Higdon <thigdon@akamai.com>

Limit the return value (corresponding to the length of the buffer to be
DMAed back to the intiator) to the value in req->cmd.xfer, which is the
amount of data that the initiator expects. Eliminate now-duplicate code
that does this guarding in the functions for individual commands.

Without this, the SCRIPTS code in the emulated LSI device eventually
raises a DMA interrupt for a data overrun when an INQUIRY command whose
buflen exceeds req->cmd.xfer is processed. It's the responsibility of
the client to provide a request buffer and allocation length that are
large enough for the result of the command.

Signed-off-by: Thomas Higdon <thigdon@akamai.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 hw/scsi-disk.c |   10 +---------
 1 files changed, 1 insertions(+), 9 deletions(-)

diff --git a/hw/scsi-disk.c b/hw/scsi-disk.c
index 5d8bf53..11cfe73 100644
--- a/hw/scsi-disk.c
+++ b/hw/scsi-disk.c
@@ -391,9 +391,6 @@ static int scsi_disk_emulate_inquiry(SCSIRequest *req, uint8_t *outbuf)
             }
 
             l = strlen(s->serial);
-            if (l > req->cmd.xfer) {
-                l = req->cmd.xfer;
-            }
             if (l > 20) {
                 l = 20;
             }
@@ -1002,9 +999,6 @@ static int scsi_disk_emulate_mode_sense(SCSIDiskReq *r, uint8_t *outbuf)
         outbuf[0] = ((buflen - 2) >> 8) & 0xff;
         outbuf[1] = (buflen - 2) & 0xff;
     }
-    if (buflen > r->req.cmd.xfer) {
-        buflen = r->req.cmd.xfer;
-    }
     return buflen;
 }
 
@@ -1038,9 +1032,6 @@ static int scsi_disk_emulate_read_toc(SCSIRequest *req, uint8_t *outbuf)
     default:
         return -1;
     }
-    if (toclen > req->cmd.xfer) {
-        toclen = req->cmd.xfer;
-    }
     return toclen;
 }
 
@@ -1251,6 +1242,7 @@ static int scsi_disk_emulate_command(SCSIDiskReq *r)
         scsi_check_condition(r, SENSE_CODE(INVALID_OPCODE));
         return -1;
     }
+    buflen = MIN(buflen, req->cmd.xfer);
     return buflen;
 
 not_ready:
-- 
1.7.6.5