From bcc3a5ea9c631645b792f151e1beb9a4b1a4e34e Mon Sep 17 00:00:00 2001
From: David Favro <dfavro@meta-dynamic.com>
Date: Sat, 23 May 2020 08:24:59 -0400
Subject: [PATCH 25/27] Detect too-small device: error rather than
 underflow/crash

For 1.x metadata, when the user requested creation of an array on
component devices that were too small even to hold the superblock,
an undetected integer wraparound (underflow) resulted in an enormous
computed size which resulted in various follow-on errors such as
floating-point exception.

This patch detects this condition, prints a reasonable diagnostic
message, and refuses to continue.

Signed-off-by: David Favro <dfavro@meta-dynamic.com>
Signed-off-by: Jes Sorensen <jsorensen@fb.com>
---
 super1.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/super1.c b/super1.c
index b85dc20..06bc145 100644
--- a/super1.c
+++ b/super1.c
@@ -2715,6 +2715,7 @@ static int validate_geometry1(struct supertype *st, int level,
 	unsigned long long ldsize, devsize;
 	int bmspace;
 	unsigned long long headroom;
+	unsigned long long overhead;
 	int fd;
 
 	if (level == LEVEL_CONTAINER) {
@@ -2747,10 +2748,6 @@ static int validate_geometry1(struct supertype *st, int level,
 	close(fd);
 
 	devsize = ldsize >> 9;
-	if (devsize < 24) {
-		*freesize = 0;
-		return 0;
-	}
 
 	/* creating:  allow suitable space for bitmap or PPL */
 	if (consistency_policy == CONSISTENCY_POLICY_PPL)
@@ -2791,15 +2788,27 @@ static int validate_geometry1(struct supertype *st, int level,
 	case 0: /* metadata at end.  Round down and subtract space to reserve */
 		devsize = (devsize & ~(4ULL*2-1));
 		/* space for metadata, bblog, bitmap/ppl */
-		devsize -= 8*2 + 8 + bmspace;
+		overhead = 8*2 + 8 + bmspace;
+		if (devsize < overhead) /* detect underflow */
+			goto dev_too_small_err;
+		devsize -= overhead;
 		break;
 	case 1:
 	case 2:
+		if (devsize < data_offset) /* detect underflow */
+			goto dev_too_small_err;
 		devsize -= data_offset;
 		break;
 	}
 	*freesize = devsize;
 	return 1;
+
+/* Error condition, device cannot even hold the overhead. */
+dev_too_small_err:
+	fprintf(stderr, "device %s is too small (%lluK) for "
+			"required metadata!\n", subdev, devsize>>1);
+	*freesize = 0;
+	return 0;
 }
 
 void *super1_make_v0(struct supertype *st, struct mdinfo *info, mdp_super_t *sb0)
-- 
2.21.1 (Apple Git-122.3)