scsi_cd: Improve TOC access validation

1. During CD probing, we read the TOC header to find the number of
   entries, then read the TOC itself.  The header determines the number
   of entries, which determines the amount of data to read from the
   device into the softc in the CD_STATE_MEDIA_TOC_FULL state.  We
   hard-code a limit of 99 tracks (plus one for the lead-out) in the
   softc, but were not validating that the size reported by the media
   would fit in this hard-coded limit.  Kernel memory corruption could
   occur if not.[1]  Add validation to check this, and refuse to cache
   the TOC if it would not fit.

2. The CDIOCPLAYTRACKS ioctl uses caller provided track numbers to index
   into the TOC, but we only validate the starting index.  Add
   validation of the ending index.

Also, raise the hard-coded limit from 100 tracks to 170, per a
suggestion from Ken.

Reported by:	C Turt <ecturt@gmail.com> [1]
Reviewed by:	ken, avg
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D32803

1 files changed, 19 insertions, 18 deletions

diff --git a/sys/cam/scsi/scsi_cd.c b/sys/cam/scsi/scsi_cd.c
index 3e8187544bff..3cca4bbf243b 100644
--- a/sys/cam/scsi/scsi_cd.c
+++ b/sys/cam/scsi/scsi_cd.c
@@ -136,9 +136,13 @@ typedef enum {
 #define ccb_state ppriv_field0
 #define ccb_bp ppriv_ptr1
 
+/*
+ * According to the MMC-6 spec, 6.25.3.2.11, the lead-out is reported by
+ * READ_TOC as logical track 170, so at most 169 tracks may be reported.
+ */
 struct cd_tocdata {
 	struct ioc_toc_header header;
-	struct cd_toc_entry entries[100];
+	struct cd_toc_entry entries[170];
 };
 
 struct cd_toc_single {
@@ -1596,12 +1600,13 @@ cddone(struct cam_periph *periph, union ccb *done_ccb)
 		}
 
 		/* Number of TOC entries, plus leadout */
-		num_entries = (toch->ending_track - toch->starting_track) + 2;
-		cdindex = toch->starting_track + num_entries -1;
+		num_entries = toch->ending_track - toch->starting_track + 2;
+		cdindex = toch->starting_track + num_entries - 1;
 
 		if ((done_ccb->ccb_h.ccb_state & CD_CCB_TYPE_MASK) ==
 		     CD_CCB_MEDIA_TOC_HDR) {
-			if (num_entries <= 0) {
+			if (num_entries <= 0 ||
+			    num_entries > nitems(softc->toc.entries)) {
 				softc->flags &= ~CD_FLAG_VALID_TOC;
 				bzero(&softc->toc, sizeof(softc->toc));
 				/*
@@ -1838,23 +1843,19 @@ cdioctl(struct disk *dp, u_long cmd, void *addr, int flag, struct thread *td)
 			 */
 			if (softc->flags & CD_FLAG_VALID_TOC) {
 				union msf_lba *sentry, *eentry;
+				struct ioc_toc_header *th;
 				int st, et;
 
-				if (args->end_track <
-				    softc->toc.header.ending_track + 1)
+				th = &softc->toc.header;
+				if (args->end_track < th->ending_track + 1)
 					args->end_track++;
-				if (args->end_track >
-				    softc->toc.header.ending_track + 1)
-					args->end_track =
-					    softc->toc.header.ending_track + 1;
-				st = args->start_track -
-					softc->toc.header.starting_track;
-				et = args->end_track -
-					softc->toc.header.starting_track;
-				if ((st < 0)
-				 || (et < 0)
-				 || (st > (softc->toc.header.ending_track -
-				     softc->toc.header.starting_track))) {
+				if (args->end_track > th->ending_track + 1)
+					args->end_track = th->ending_track + 1;
+				st = args->start_track - th->starting_track;
+				et = args->end_track - th->starting_track;
+				if (st < 0 || et < 0 ||
+				    st > th->ending_track - th->starting_track ||
+				    et > th->ending_track - th->starting_track) {
 					error = EINVAL;
 					cam_periph_unlock(periph);
 					break;