3027 installgrub can segfault when encountering bogus data on disk

*** 401,411 ****
                      device_path);
                  retval = BC_NOEINFO;
                  goto out_dev;
          }
  
!         einfo = find_einfo(stage2->extra);
          if (einfo == NULL) {
                  retval = BC_NOEINFO;
                  (void) fprintf(stderr, gettext("No extended information "
                      "found\n"));
                  goto out_dev;
--- 401,411 ----
                      device_path);
                  retval = BC_NOEINFO;
                  goto out_dev;
          }
  
!         einfo = find_einfo(stage2->extra, stage2->extra_size);
          if (einfo == NULL) {
                  retval = BC_NOEINFO;
                  (void) fprintf(stderr, gettext("No extended information "
                      "found\n"));
                  goto out_dev;
*** 499,509 ****
                      "stage2\n", curr_device->path);
                  retval = BC_NOEXTRA;
                  goto out_devs;
          }
  
!         einfo_curr = find_einfo(stage2_curr->extra);
          if (einfo_curr != NULL)
                  updt_str = einfo_get_string(einfo_curr);
  
          write_mbr = B_TRUE;
          force_mbr = B_TRUE;
--- 499,509 ----
                      "stage2\n", curr_device->path);
                  retval = BC_NOEXTRA;
                  goto out_devs;
          }
  
!         einfo_curr = find_einfo(stage2_curr->extra, stage2_curr->extra_size);
          if (einfo_curr != NULL)
                  updt_str = einfo_get_string(einfo_curr);
  
          write_mbr = B_TRUE;
          force_mbr = B_TRUE;
*** 1219,1228 ****
--- 1219,1229 ----
          stage2->file = stage2->buf;
          stage2->file_size = size;
          stage2->mboot_off = mboot_off;
          stage2->mboot = (multiboot_header_t *)(stage2->buf + stage2->mboot_off);
          stage2->extra = stage2->buf + P2ROUNDUP(stage2->file_size, 8);
+         stage2->extra_size = stage2->buf_size - P2ROUNDUP(stage2->file_size, 8);
  
          return (BC_SUCCESS);
  }
  
  static boolean_t
*** 1249,1259 ****
  
          /*
           * Look for the extended information structure in the extra payload
           * area.
           */
!         einfo = find_einfo(stage2_disk.extra);
          if (einfo == NULL) {
                  BOOT_DEBUG("No extended information available\n");
                  return (B_TRUE);
          }
  
--- 1250,1260 ----
  
          /*
           * Look for the extended information structure in the extra payload
           * area.
           */
!         einfo = find_einfo(stage2_disk.extra, stage2_disk.extra_size);
          if (einfo == NULL) {
                  BOOT_DEBUG("No extended information available\n");
                  return (B_TRUE);
          }