scsi: fix scsi_convert_sense crash when in_buf == NULL && in_len == 0

scsi_disk_emulate_command passes in_buf == NULL when sent a REQUEST
SENSE command.  Check for in_len == 0 before dereferencing in_buf.

Fixes: f68d98b21fa74155dc7c1fd212474379ac3c7531
Reported-by: Roman Kagan <rkagan@virtuozzo.com>
Tested-by: Roman Kagan <rkagan@virtuozzo.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 6 insertions, 6 deletions

diff --git a/scsi/utils.c b/scsi/utils.c
index ddae650a99..8738522955 100644
--- a/scsi/utils.c
+++ b/scsi/utils.c
@@ -322,18 +322,18 @@ int scsi_convert_sense(uint8_t *in_buf, int in_len,
     SCSISense sense;
     bool fixed_in;
 
+    if (in_len == 0) {
+        return scsi_build_sense_buf(buf, len, SENSE_CODE(NO_SENSE), fixed);
+    }
+
     fixed_in = (in_buf[0] & 2) == 0;
-    if (in_len && fixed == fixed_in) {
+    if (fixed == fixed_in) {
         memcpy(buf, in_buf, MIN(len, in_len));
         return MIN(len, in_len);
-    }
-
-    if (in_len == 0) {
-        sense = SENSE_CODE(NO_SENSE);
     } else {
         sense = scsi_parse_sense_buf(in_buf, in_len);
+        return scsi_build_sense_buf(buf, len, sense, fixed);
     }
-    return scsi_build_sense_buf(buf, len, sense, fixed);
 }
 
 int scsi_sense_to_errno(int key, int asc, int ascq)