From: krw <krw@openbsd.org>
Date: Tue, 1 Jun 2021 22:54:43 +0000 (+0000)
Subject: Make spoofed disklabel boundstart and boundend default to the bounds
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=ba6b8b61ba44d8e2d6cfe29447a1054c2cc7f280;p=openbsd

Make spoofed disklabel boundstart and boundend default to the bounds
of the usable LBA range defined by the GPT header. And then shrink
them to the bounds of the first OpenBSD partition if one is found.

While here simplify the logic, eliminate some superfluous variables
and reduce use of magic numbers.

Improvement suggested by sobrado@ ok kettenis@
---

diff --git a/sys/kern/subr_disk.c b/sys/kern/subr_disk.c
index ba1b8c1782d..31b342ccc83 100644
--- a/sys/kern/subr_disk.c
+++ b/sys/kern/subr_disk.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: subr_disk.c,v 1.242 2021/05/27 14:27:41 krw Exp $	*/
+/*	$OpenBSD: subr_disk.c,v 1.243 2021/06/01 22:54:43 krw Exp $	*/
 /*	$NetBSD: subr_disk.c,v 1.17 1996/03/16 23:17:08 christos Exp $	*/
 
 /*
@@ -749,17 +749,17 @@ spoofgptlabel(struct buf *bp, void (*strat)(struct buf *),
 	static const u_int8_t gpt_uuid_openbsd[] = GPT_UUID_OPENBSD;
 	struct gpt_header gh;
 	struct uuid uuid_part, uuid_openbsd;
-	struct gpt_partition *gp, *gp_tmp;
+	struct gpt_partition *gp;
 	struct partition *pp;
 	size_t gpsz;
-	u_int64_t ghlbaend, ghlbastart, gptpartoff, gptpartend, sector;
+	u_int64_t ghlbaend, ghlbastart, sector;
 	u_int64_t start, end;
-	int i, altheader = 0, error, n;
+	int i, error, found, n;
 	uint32_t ghpartnum;
 
 	uuid_dec_be(gpt_uuid_openbsd, &uuid_openbsd);
 
-	for (sector = GPTSECTOR; ; sector = DL_GETDSIZE(lp)-1, altheader = 1) {
+	for (sector = GPTSECTOR; ; sector = DL_GETDSIZE(lp) - 1) {
 		uint64_t ghpartlba;
 		uint32_t ghpartsize;
 		uint32_t ghpartspersec;
@@ -773,7 +773,7 @@ spoofgptlabel(struct buf *bp, void (*strat)(struct buf *),
 		bcopy(bp->b_data, &gh, sizeof(gh));
 
 		if (gpt_chk_hdr(&gh, lp)) {
-			if (altheader) {
+			if (sector != GPTSECTOR) {
 				DPRINTF("alternate header also broken\n");
 				return (EINVAL);
 			}
@@ -798,9 +798,8 @@ spoofgptlabel(struct buf *bp, void (*strat)(struct buf *),
 		* XXX:	Fails if # of partition entries is not a multiple of
 		*	ghpartspersec.
 		*/
-		sector = ghpartlba;
-		for (i = 0; i < ghpartnum / ghpartspersec; i++, sector++) {
-			error = readdisksector(bp, strat, lp, sector);
+		for (i = 0; i < ghpartnum / ghpartspersec; i++) {
+			error = readdisksector(bp, strat, lp, ghpartlba + i);
 			if (error) {
 				free(gp, M_DEVBUF, gpsz);
 				return (error);
@@ -812,7 +811,7 @@ spoofgptlabel(struct buf *bp, void (*strat)(struct buf *),
 
 		if (gpt_chk_parts(&gh, gp)) {
 			free(gp, M_DEVBUF, gpsz);
-			if (altheader) {
+			if (letoh64(gh.gh_lba_self) != GPTSECTOR) {
 				DPRINTF("alternate partition entries are also "
 				    "broken\n");
 				return (EINVAL);
@@ -823,44 +822,34 @@ spoofgptlabel(struct buf *bp, void (*strat)(struct buf *),
 	}
 
 	/* Find OpenBSD partition and spoof others along the way. */
-	n = 0;
-	gptpartoff = 0;
-	gptpartend = DL_GETBEND(lp);
-	for (gp_tmp = gp, i = 0; i < ghpartnum; gp_tmp++, i++) {
-		start = letoh64(gp_tmp->gp_lba_start);
-		end = letoh64(gp_tmp->gp_lba_end);
+	DL_SETBSTART(lp, ghlbastart);
+	DL_SETBEND(lp, ghlbaend + 1);
+	found = 0;
+	n = 'i' - 'a';	/* Start spoofing at 'i', a.k.a. 8. */
+	for (i = 0; i < ghpartnum; i++) {
+		start = letoh64(gp[i].gp_lba_start);
+		end = letoh64(gp[i].gp_lba_end);
 		if (start > end || start < ghlbastart || end > ghlbaend)
 			continue; /* entry invalid */
 
-		uuid_dec_le(&gp_tmp->gp_type, &uuid_part);
-		if (!memcmp(&uuid_part, &uuid_openbsd, sizeof(struct uuid))) {
-			if (gptpartoff == 0) {
-				gptpartoff = start;
-				gptpartend = end + 1;
+		uuid_dec_le(&gp[i].gp_type, &uuid_part);
+		if (memcmp(&uuid_part, &uuid_openbsd, sizeof(struct uuid)) == 0) {
+			if (found == 0) {
+				found = 1;
+				DL_SETBSTART(lp, start);
+				DL_SETBEND(lp, end + 1);
 			}
-			continue; /* Do *NOT* spoof OpenBSD partitions! */
+		} else if (n < MAXPARTITIONS) {
+			pp = &lp->d_partitions[n];
+			n++;
+			pp->p_fstype = gpt_get_fstype(&uuid_part);
+			DL_SETPOFFSET(pp, start);
+			DL_SETPSIZE(pp, end - start + 1);
 		}
-
-		 /*
-		 * Don't try to spoof more than 8 partitions, i.e.
-		 * 'i' -'p'.
-		 */
-		if (n >= 8)
-			continue;
-
-		pp = &lp->d_partitions[8+n];
-		n++;
-		pp->p_fstype = gpt_get_fstype(&uuid_part);
-		DL_SETPOFFSET(pp, start);
-		DL_SETPSIZE(pp, end - start + 1);
 	}
 
 	free(gp, M_DEVBUF, gpsz);
 
-	DL_SETBSTART(lp, gptpartoff);
-	DL_SETBEND(lp, (gptpartend < DL_GETDSIZE(lp)) ? gptpartend :
-	    DL_GETDSIZE(lp));
-
 	return (0);
 }