Don't permit generation of non-physical disk addresses.

subr_diskmbr.c:
Don't "helpfully" enlarge our idea of the disk size to cover all the
primary slices.  Instead, truncate or discard slices that don't seem
to be on the disk.  The enlargement was a hack for disks that don't
report their size (e.g., MFM disks).  It is just wrong in general.

wd.c:
In CHS mode, limit the disk size so that cylinder numbers >= 65536
cannot occur.  This normally only affects disks larger than 33.8GB.
CHS mode accesses to addresses above the limit are now properly broken
(an error is returned instead of garbage for reads and disk corruption
for writes).

PR:		15611
Reviewed by:	readers of freebsd-bugs did not respond to a request
            	for review

1 files changed, 59 insertions, 20 deletions

diff --git a/sys/kern/subr_diskmbr.c b/sys/kern/subr_diskmbr.c
index 591fc8bf40f2..c16f5d7346bb 100644
--- a/sys/kern/subr_diskmbr.c
+++ b/sys/kern/subr_diskmbr.c
@@ -73,6 +73,9 @@ static void mbr_extended __P((dev_t dev, struct disklabel *lp,
 			      u_long ext_size, u_long base_ext_offset,
 			      int nsectors, int ntracks, u_long mbr_offset,
 			      int level));
+static int mbr_setslice __P((char *sname, struct disklabel *lp,
+			     struct diskslice *sp, struct dos_partition *dp,
+			     u_long br_offset));
 
 static int
 check_part(sname, dp, offset, nsectors, ntracks, mbr_offset )
@@ -294,14 +297,26 @@ reread_mbr:
 	 */
 	secpercyl = (u_long)max_nsectors * max_ntracks;
 	if (secpercyl != 0) {
+#if 0
 		u_long	secperunit;
+#endif
 
 		lp->d_nsectors = max_nsectors;
 		lp->d_ntracks = max_ntracks;
 		lp->d_secpercyl = secpercyl;
+		/*
+		 * Temporarily, don't even consider adjusting the drive's
+		 * size, since the adjusted size may exceed the hardware's
+		 * addressing capabilities.  The adjustment helped mainly
+		 * for ancient MFM drives with > 1024 cylinders, but now
+		 * breaks at least IDE drives with 63*16*65536 sectors if
+		 * they are controlled by the wd driver in CHS mode.
+		 */
+#if 0
 		secperunit = secpercyl * max_ncyls;
 		if (lp->d_secperunit < secperunit)
 			lp->d_secperunit = secperunit;
+#endif
 		lp->d_ncylinders = lp->d_secperunit / secpercyl;
 	}
 
@@ -319,18 +334,9 @@ reread_mbr:
 	/* Initialize normal slices. */
 	sp = &ssp->dss_slices[BASE_SLICE];
 	for (dospart = 0, dp = dp0; dospart < NDOSPART; dospart++, dp++, sp++) {
-		sp->ds_offset = mbr_offset + dp->dp_start;
-		sp->ds_size = dp->dp_size;
-		sp->ds_type = dp->dp_typ;
-#ifdef PC98_ATCOMPAT
-		/* Fake FreeBSD(98). */
-		if (sp->ds_type == DOSPTYP_386BSD)
-			sp->ds_type = 0x94;
-#endif
-#if 0
-		lp->d_subtype |= (lp->d_subtype & 3) | dospart
-				 | DSTYPE_INDOSPART;
-#endif
+		sname = dsname(dev, dkunit(dev), BASE_SLICE + dospart,
+			       RAW_PART, partname);
+		(void)mbr_setslice(sname, lp, sp, dp, mbr_offset);
 	}
 	ssp->dss_nslices = BASE_SLICE + NDOSPART;
 
@@ -451,14 +457,8 @@ mbr_extended(dev, lp, ssp, ext_offset, ext_size, base_ext_offset, nsectors,
 				continue;
 			}
 			sp = &ssp->dss_slices[slice];
-			sp->ds_offset = ext_offset + dp->dp_start;
-			sp->ds_size = dp->dp_size;
-			sp->ds_type = dp->dp_typ;
-#ifdef PC98_ATCOMPAT
-			/* Fake FreeBSD(98). */
-			if (sp->ds_type == DOSPTYP_386BSD)
-				sp->ds_type = 0x94;
-#endif
+			if (mbr_setslice(sname, lp, sp, dp, ext_offset) != 0)
+				continue;
 			slice++;
 		}
 	}
@@ -476,6 +476,45 @@ done:
 	brelse(bp);
 }
 
+static int
+mbr_setslice(sname, lp, sp, dp, br_offset)
+	char	*sname;
+	struct disklabel *lp;
+	struct diskslice *sp;
+	struct dos_partition *dp;
+	u_long	br_offset;
+{
+	u_long	offset;
+	u_long	size;
+
+	offset = br_offset + dp->dp_start;
+	if (offset > lp->d_secperunit || offset < br_offset) {
+		printf(
+		"%s: slice starts beyond end of the disk: rejecting it\n",
+		       sname);
+		return (1);
+	}
+	size = lp->d_secperunit - offset;
+	if (size >= dp->dp_size)
+		size = dp->dp_size;
+	else
+		printf(
+"%s: slice extends beyond end of disk: truncating from %lu to %lu sectors\n",
+		       sname, (u_long)dp->dp_size, size);
+	sp->ds_offset = offset;
+	sp->ds_size = size;
+	sp->ds_type = dp->dp_typ;
+#ifdef PC98_ATCOMPAT
+	/* Fake FreeBSD(98). */
+	if (sp->ds_type == DOSPTYP_386BSD)
+		sp->ds_type = 0x94;
+#endif
+#if 0
+	lp->d_subtype |= (lp->d_subtype & 3) | dospart | DSTYPE_INDOSPART;
+#endif
+	return (0);
+}
+
 #ifdef __alpha__
 void
 alpha_fix_srm_checksum(bp)