From: krw <krw@openbsd.org>
Date: Mon, 28 Jun 2021 19:50:30 +0000 (+0000)
Subject: Add another epicycle to -A processing that ensures ONLY the
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=c2fbfd6da5b34b8fca89fa08d3444919765b5d9a;p=openbsd

Add another epicycle to -A processing that ensures ONLY the
partition table is changed. Not the GPT header. Not the MBR. And
only write back as much partition table information as the header
claims to have room for.

At a minimum should make -A safer when operating on the Apple M1
GPT.

A major overhaul of this code is urgently needed before someone
sneezes too hard in its vicinity.

Feedback kettenis@ & ok deraadt@
---

diff --git a/sbin/fdisk/cmd.c b/sbin/fdisk/cmd.c
index 777e48bea71..76701b11f13 100644
--- a/sbin/fdisk/cmd.c
+++ b/sbin/fdisk/cmd.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: cmd.c,v 1.117 2021/06/21 02:05:30 krw Exp $	*/
+/*	$OpenBSD: cmd.c,v 1.118 2021/06/28 19:50:30 krw Exp $	*/
 
 /*
  * Copyright (c) 1997 Tobias Weingartner
@@ -63,7 +63,7 @@ Xreinit(char *args, struct mbr *mbr)
 
 	if (dogpt) {
 		MBR_init_GPT(mbr);
-		GPT_init();
+		GPT_init(GHANDGP, 0);
 		GPT_print("s", TERSE);
 	} else {
 		memset(&gh, 0, sizeof(gh));
diff --git a/sbin/fdisk/fdisk.c b/sbin/fdisk/fdisk.c
index b1f3870a964..59a43da8daf 100644
--- a/sbin/fdisk/fdisk.c
+++ b/sbin/fdisk/fdisk.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: fdisk.c,v 1.113 2021/06/25 19:24:53 krw Exp $	*/
+/*	$OpenBSD: fdisk.c,v 1.114 2021/06/28 19:50:30 krw Exp $	*/
 
 /*
  * Copyright (c) 1997 Tobias Weingartner
@@ -222,14 +222,14 @@ main(int argc, char *argv[])
 		if (letoh64(gh.gh_sig) != GPTSIGNATURE)
 			errx(1, "-A requires a valid GPT");
 		else {
-			MBR_init_GPT(&initial_mbr);
-			GPT_init();
+			initial_mbr = mbr;	/* Keep current MBR. */
+			GPT_init(GPONLY, b_sectors);
 			query = "Do you wish to write new GPT?";
 		}
 	} else if (i_flag) {
 		if (g_flag) {
 			MBR_init_GPT(&initial_mbr);
-			GPT_init();
+			GPT_init(GHANDGP, b_sectors);
 			query = "Do you wish to write new GPT?";
 		} else {
 			memset(&gh, 0, sizeof(gh));
diff --git a/sbin/fdisk/gpt.c b/sbin/fdisk/gpt.c
index 83e5201f58d..df8b0f2240a 100644
--- a/sbin/fdisk/gpt.c
+++ b/sbin/fdisk/gpt.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: gpt.c,v 1.33 2021/06/25 19:24:53 krw Exp $	*/
+/*	$OpenBSD: gpt.c,v 1.34 2021/06/28 19:50:30 krw Exp $	*/
 /*
  * Copyright (c) 2015 Markus Muller <mmu@grummel.net>
  * Copyright (c) 2015 Kenneth R Westerback <krw@openbsd.org>
@@ -49,7 +49,7 @@ int			  add_partition(const uint8_t *, const char *, uint64_t);
 int			  get_header(off_t);
 int			  get_partition_table(void);
 int			  init_gh(void);
-int			  init_gp(void);
+int			  init_gp(int, uint32_t);
 
 int
 get_header(off_t where)
@@ -413,17 +413,15 @@ init_gh(void)
 }
 
 int
-init_gp(void)
+init_gp(int how, uint32_t bootsectors)
 {
-	extern uint32_t b_sectors;
-	extern int A_flag;
 	const uint8_t gpt_uuid_efi_system[] = GPT_UUID_EFI_SYSTEM;
 	const uint8_t gpt_uuid_openbsd[] = GPT_UUID_OPENBSD;
 	struct gpt_partition oldgp[NGPTPARTITIONS];
 	int pn, rslt;
 
 	memcpy(&oldgp, &gp, sizeof(oldgp));
-	if (A_flag == 0)
+	if (how == GHANDGP)
 		memset(&gp, 0, sizeof(gp));
 	else {
 		for (pn = 0; pn < NGPTPARTITIONS; pn++) {
@@ -434,9 +432,9 @@ init_gp(void)
 	}
 
 	rslt = 0;
-	if (b_sectors > 0) {
+	if (bootsectors > 0) {
 		rslt = add_partition(gpt_uuid_efi_system, "EFI System Area",
-		    b_sectors);
+		    bootsectors);
 	}
 	if (rslt == 0)
 		rslt = add_partition(gpt_uuid_openbsd, "OpenBSD Area", 0);
@@ -448,13 +446,14 @@ init_gp(void)
 }
 
 int
-GPT_init(void)
+GPT_init(int how, uint32_t bootsectors)
 {
-	int rslt;
+	int rslt = 0;
 
-	rslt = init_gh();
+	if (how == GHANDGP)
+		rslt = init_gh();
 	if (rslt == 0)
-		rslt = init_gp();
+		rslt = init_gp(how, bootsectors);
 
 	return rslt;
 }
@@ -498,10 +497,9 @@ GPT_write(void)
 	uint64_t altgh, altgp, prigh, prigp, gpbytes;
 
 	/*
-	 * XXX Assume we always write full-size partition table.
 	 * XXX Assume size of gp is multiple of sector size.
 	 */
-	gpbytes = sizeof(gp);
+	gpbytes = letoh64(gh.gh_part_num) * letoh64(gh.gh_part_size);
 
 	prigh = GPTSECTOR;
 	prigp = prigh + 1;
diff --git a/sbin/fdisk/gpt.h b/sbin/fdisk/gpt.h
index f349b81ba26..69531c05a65 100644
--- a/sbin/fdisk/gpt.h
+++ b/sbin/fdisk/gpt.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: gpt.h,v 1.12 2021/06/16 15:40:47 krw Exp $	*/
+/*	$OpenBSD: gpt.h,v 1.13 2021/06/28 19:50:30 krw Exp $	*/
 /*
  * Copyright (c) 2015 Markus Muller <mmu@grummel.net>
  * Copyright (c) 2015 Kenneth R Westerback <krw@openbsd.org>
@@ -20,7 +20,7 @@ void		GPT_read(int);
 int		GPT_get_lba_start(unsigned int);
 int		GPT_get_lba_end(unsigned int);
 
-int		GPT_init(void);
+int		GPT_init(int, uint32_t);
 int		GPT_write(void);
 void		GPT_zap_headers(void);
 void		GPT_print(char *, int);
@@ -36,3 +36,6 @@ extern struct gpt_partition gp[NGPTPARTITIONS];
 
 #define	TERSE		0
 #define	VERBOSE		1
+
+#define	GHANDGP		0
+#define	GPONLY		1