[Qemu-stable] [PATCH] scsi: fix buffer overflow in scsi_req_parse_cdb (CVE-2015-5158)

[Paolo Bonzini]

This is a guest-triggerable buffer overflow present in QEMU 2.2.0
and newer.  scsi_cdb_length returns -1 as an error value, but the
caller does not check it.

Luckily, the massive overflow means that QEMU will just SIGSEGV,
making the impact much smaller.

Reported-by: Zhu Donghai (朱东海) <address@hidden>
Fixes: 1894df02811f6b79ea3ffbf1084599d96f316173
Cc: address@hidden
---
 hw/scsi/scsi-bus.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/hw/scsi/scsi-bus.c b/hw/scsi/scsi-bus.c
index f50b2f0..f0ae462 100644
--- a/hw/scsi/scsi-bus.c
+++ b/hw/scsi/scsi-bus.c
@@ -1239,10 +1239,15 @@ int scsi_cdb_length(uint8_t *buf) {
 int scsi_req_parse_cdb(SCSIDevice *dev, SCSICommand *cmd, uint8_t *buf)
 {
     int rc;
+    int len;
 
     cmd->lba = -1;
-    cmd->len = scsi_cdb_length(buf);
+    len = scsi_cdb_length(buf);
+    if (len < 0) {
+        return -1;
+    }
 
+    cmd->len = len;
     switch (dev->type) {
     case TYPE_TAPE:
         rc = scsi_req_stream_xfer(cmd, dev, buf);
-- 
2.4.3