From cb56711d68b21fbc890ddd586604e7f3bdedca4d Mon Sep 17 00:00:00 2001
From: Mark Johnston <markj@FreeBSD.org>
Date: Sat, 5 Jan 2019 15:28:20 +0000
Subject: [PATCH] Add a bounds check to the tws(4) passthrough ioctl handler.

tws_passthru() was doing a copyin of a user-specified request
without validating its length, so a malicious request could overrun
the buffer.  By default, the tws(4) device file is only accessible
as root.

admbug:		825
Reported by:	Anonymous of the Shellphish Grill Team
Reviewed by:	delphij
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D18536
---
 sys/dev/tws/tws_user.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/sys/dev/tws/tws_user.c b/sys/dev/tws/tws_user.c
index a3970f0af40..2afdccbf7b4 100644
--- a/sys/dev/tws/tws_user.c
+++ b/sys/dev/tws/tws_user.c
@@ -92,9 +92,13 @@ tws_passthru(struct tws_softc *sc, void *buf)
     struct tws_request *req;
     struct tws_ioctl_no_data_buf *ubuf = (struct tws_ioctl_no_data_buf *)buf;
     int error;
+    u_int32_t buffer_length;
     u_int16_t lun4;
 
-
+    buffer_length = roundup2(ubuf->driver_pkt.buffer_length, 512);
+    if ( buffer_length > TWS_MAX_IO_SIZE ) {
+        return(EINVAL);
+    }
     if ( tws_get_state(sc) != TWS_ONLINE) {
         return(EBUSY);
     }
@@ -118,7 +122,7 @@ tws_passthru(struct tws_softc *sc, void *buf)
         }
     } while(1);
 
-    req->length = (ubuf->driver_pkt.buffer_length + 511) & ~511;
+    req->length = buffer_length;
     TWS_TRACE_DEBUG(sc, "datal,rid", req->length, req->request_id);
     if ( req->length ) {
         req->data = sc->ioctl_data_mem;