Make EBR probe method less strictly to be able detect EBRs with

small non fatal inconsistency. EBR may contain boot loader and sometimes
it just has some garbage data. Now this does not prevent FreeBSD to use
extended partitions. But since we do not support bootcode for EBR we mark
tables which have non empty boot area as corrupt. This does make them
readonly and we can not damage this data.

PR:		kern/141235
MFC after:	1 month

1 files changed, 25 insertions, 21 deletions

diff --git a/sys/geom/part/g_part_ebr.c b/sys/geom/part/g_part_ebr.c
index f16f42a..115162e 100644
--- a/sys/geom/part/g_part_ebr.c
+++ b/sys/geom/part/g_part_ebr.c
@@ -377,7 +377,7 @@ g_part_ebr_probe(struct g_part_table *table, struct g_consumer *cp)
 	char psn[8];
 	struct g_provider *pp;
 	u_char *buf, *p;
-	int error, index, res, sum;
+	int error, index, res;
 	uint16_t magic;
 
 	pp = cp->provider;
@@ -409,29 +409,11 @@ g_part_ebr_probe(struct g_part_table *table, struct g_consumer *cp)
 	if (magic != DOSMAGIC)
 		goto out;
 
-	/*
-	 * The sector is all zeroes, except for the partition entries,
-	 * pseudo boot code and some signatures or disk serial number.
-	 * The latter can be found in the 9 bytes immediately in front
-	 * of the partition table.
-	 */
-	sum = 0;
-	for (index = 96; index < DOSPARTOFF - 9; index++)
-		sum += buf[index];
-	if (sum != 0)
-		goto out;
-
-	for (index = 0; index < NDOSPART; index++) {
+	for (index = 0; index < 2; index++) {
 		p = buf + DOSPARTOFF + index * DOSPARTSIZE;
 		if (p[0] != 0 && p[0] != 0x80)
 			goto out;
-		if (index < 2)
-			continue;
-		/* The 3rd & 4th entries are always zero. */
-		if ((le64dec(p+0) + le64dec(p+8)) != 0)
-			goto out;
 	}
-
 	res = G_PART_PROBE_PRI_NORM;
 
  out:
@@ -450,7 +432,7 @@ g_part_ebr_read(struct g_part_table *basetable, struct g_consumer *cp)
 	u_char *buf;
 	off_t ofs, msize;
 	u_int lba;
-	int error, index;
+	int error, index, sum;
 
 	pp = cp->provider;
 	table = (struct g_part_ebr_table *)basetable;
@@ -465,6 +447,28 @@ g_part_ebr_read(struct g_part_table *basetable, struct g_consumer *cp)
 
 		ebr_entry_decode(buf + DOSPARTOFF + 0 * DOSPARTSIZE, ent + 0);
 		ebr_entry_decode(buf + DOSPARTOFF + 1 * DOSPARTSIZE, ent + 1);
+
+		/* The 3rd & 4th entries should be zeroes. */
+		if (le64dec(buf + DOSPARTOFF + 2 * DOSPARTSIZE) +
+		    le64dec(buf + DOSPARTOFF + 3 * DOSPARTSIZE) != 0) {
+			basetable->gpt_corrupt = 1;
+			printf("GEOM: %s: invalid entries in the EBR ignored.\n",
+			    pp->name);
+		}
+		/* We do not support bootcode for EBR. If bootcode area is
+		 * not zeroes, then mark this EBR as corrupt to do not break
+		 * anything for another OS'es.
+		 */
+		if (lba == 0) {
+			sum = 0;
+			for (index = 0; index < DOSPARTOFF; index++)
+				sum += buf[index];
+			if (sum != 0) {
+				basetable->gpt_corrupt = 1;
+				printf("GEOM: %s: EBR has non empty bootcode.\n",
+				    pp->name);
+			}
+		}
 		g_free(buf);
 
 		if (ent[0].dp_typ == 0)