From 5838ce64a2a009eb9b6164aa424ecbeb849b46ca Mon Sep 17 00:00:00 2001
From: Simon Rettberg
Date: Wed, 7 Oct 2020 14:52:44 +0200
Subject: [dev] More sanity checks, fallback to GPT if MBR yields nothing

---
 modules/dev.inc | 85 +++++++++++++++++++++++++++++++++------------------------
 1 file changed, 49 insertions(+), 36 deletions(-)

diff --git a/modules/dev.inc b/modules/dev.inc
index 1ac57d3..f213fa0 100644
--- a/modules/dev.inc
+++ b/modules/dev.inc
@@ -79,53 +79,66 @@ dev_get_type() {
 	elif [ "$( dd if="$dev" bs=1 count=8 skip=4096 2> /dev/null )" = "EFI PART" ]; then
 		gpt=4096
 	fi
+	# Check if mbr signatur is there, no GPT label was in uevent, and no protective MBR
+	local t1="$( __read_mbrid "$dev" 0 1 )"
 	if [ -z "$label" ] && [ "$number" -lt 1000 ]  && [ "$number" -gt 0 ] \
-			&& [ "$( __read_mbrsig "$dev" 0 )" = "55aa" ]; then
-		# Get MBR ID
-		if [ "$number" -le 4 ]; then
-			# Primary
-			mbrid="$( __read_mbrid "$dev" 0 "$number" )"
-		else
+			&& [ "$t1" != "ee" ] && [ "$( __read_mbrsig "$dev" 0 )" = "55aa" ]; then
+		# Then we consider parsing this as MBR
+		if [ "$number" -le 4 ]; then # 1-4 are primary partitions
+			# Validate start LBA matches sysfs
+			log_start="$( __read_mbrstart "$dev" 0 "$number" )"
+			if [ "$pstart" != "$log_start" ]; then
+				echo "Found partition $number, but start mismatch (want: $pstart found: $log_start)" >&2
+			else
+				mbrid="$( __read_mbrid "$dev" 0 "$number" )"
+				return 0
+			fi
+		else # part number 5+ -- must be logical volume in extended partition
 			# Scan for Primary type 05, scan linked list of fake MBRs from there
 			local no id ex_start log_id log_start next_id next_start current
 			for no in 1 2 3 4; do
 				id="$( __read_mbrid "$dev" 0 "$no" )"
-				echo "Scanning. Primary $no is type $id" >&2
 				[ "$id" = "05" ] && break
 			done
 			if [ "$id" != "05" ]; then
 				echo "No matching extended primary partition found" >&2
-				return 1
-			fi
-			ex_start="$( __read_mbrstart "$dev" 0 "$no" )"
-			current="$ex_start"
-			no=5 # Count through logical partitions
-			while [ "$no" != 0 ]; do
-				[ "$( __read_mbrsig "$dev" "$current" )" = "55aa" ] || break
-				log_id="$( __read_mbrid "$dev" "$current" 1 )"
-				if [ "$no" = "$number" ]; then
-					log_start="$( __read_mbrstart "$dev" "$current" 1 )"
-					log_start="$(( log_start + current ))"
-					if [ "$pstart" != "$log_start" ]; then
-						echo "Found partition $no, but start mismatch (want: $pstart found: $log_start)" >&2
-						return 1
+			else
+				echo "Primary $no is extended partition" >&2
+				ex_start="$( __read_mbrstart "$dev" 0 "$no" )"
+				current="$ex_start"
+				no=5 # Count through logical partitions. These start at 5.
+				while [ "$no" -le "$number" ]; do
+					if [ "$( __read_mbrsig "$dev" "$current" )" != "55aa" ]; then
+						echo "Unexpected end of logical partition list" >&2
+						break
 					fi
-					mbrid="$log_id"
-					break
-				fi
-				next_id="$( __read_mbrid "$dev" "$current" 2 )"
-				next_start="$( __read_mbrstart "$dev" "$current" 2 )"
-				echo "Extended id $log_id, next $next_id, $next_start" >&2
-				if [ "$next_id" = "05" ] && [ "$next_start" -gt 0 ]; then
-					current="$(( next_start + ex_start ))"
-					no="$(( no + 1 ))"
-				else
-					return 1 # End of linked list
-				fi
-			done
+					log_id="$( __read_mbrid "$dev" "$current" 1 )"
+					if [ "$no" -eq "$number" ]; then
+						log_start="$( __read_mbrstart "$dev" "$current" 1 )"
+						# logical partition's start is relative to its fake MBR
+						log_start="$(( log_start + current ))"
+						if [ "$pstart" != "$log_start" ]; then
+							echo "Found partition $no, but start mismatch (want: $pstart found: $log_start)" >&2
+							break
+						fi
+						mbrid="$log_id"
+						return 0
+					fi
+					next_id="$( __read_mbrid "$dev" "$current" 2 )"
+					# next logical partition's fake MBR is relative to the extended partition's start
+					next_start="$( __read_mbrstart "$dev" "$current" 2 )"
+					echo "Extended id $log_id, next $next_id, $next_start" >&2
+					if [ "$next_id" = "05" ] && [ "$next_start" -ge 512 ]; then
+						current="$(( next_start + ex_start ))"
+						no="$(( no + 1 ))" # Increase counter for next logical partition
+					else
+						break
+					fi
+				done
+			fi
 		fi
-		return 0
-	elif [ -n "$gpt" ]; then
+	fi
+	if [ -n "$gpt" ]; then
 		# GPT
 		local table_start current entries no entry_size log_start
 		table_start="$( __read_le "$dev" "$(( gpt + 72 ))" 8 )"
-- 
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