From 2011a616aa533c336f9242f25017ce7043557e4c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Thomas=20Wei=C3=9Fschuh?= <thomas@t-8ch.de>
Date: Tue, 6 Aug 2024 19:07:48 +0200
Subject: [PATCH] libblkid: apfs: validate checksums
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The apfs superblock contains a checksum based on Fletcher-64.
Validate the checksum to make the probing more robust.

Signed-off-by: Thomas Weißschuh <thomas@t-8ch.de>
Reference:https://github.com/util-linux/util-linux/commit/2011a616aa533c336f9242f25017ce7043557e4c
Conflict:NA
---
 libblkid/src/superblocks/apfs.c | 36 ++++++++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/libblkid/src/superblocks/apfs.c b/libblkid/src/superblocks/apfs.c
index b7f09f33..4557abcb 100644
--- a/libblkid/src/superblocks/apfs.c
+++ b/libblkid/src/superblocks/apfs.c
@@ -35,7 +35,38 @@ struct apfs_super_block {
 	uint64_t read_only_features;
 	uint64_t incompatible_features;
 	uint8_t uuid[16];
-};
+
+	uint8_t padding[4008]; // Pad to 4096 bytes for checksum
+} __attribute__((packed));
+
+static uint64_t apfs_fletcher64(const uint8_t *buf, size_t size)
+{
+	uint64_t lo32 = 0, hi32 = 0, csum_hi;
+	uint32_t csum_low;
+	size_t i;
+
+	for (i = 0; i < size / 4; i++) {
+		lo32 += le32_to_cpu(((uint32_t *)buf)[i]);
+		hi32 += lo32;
+	}
+
+	csum_low = ~((lo32 + hi32) % UINT32_MAX);
+	csum_hi = ~((lo32 + csum_low) % UINT32_MAX);
+
+	return csum_hi << 32 | csum_low;
+}
+
+static int apfs_verify_checksum(blkid_probe pr,
+				const struct apfs_super_block *sb)
+{
+	const size_t csummed_start_offset = offsetof(__typeof__(*sb), oid);
+	uint64_t csum;
+
+	csum = apfs_fletcher64(((const uint8_t *)sb) + csummed_start_offset,
+			       sizeof(*sb) - csummed_start_offset);
+
+	return blkid_probe_verify_csum(pr, csum, le64_to_cpu(sb->checksum));
+}
 
 static int probe_apfs(blkid_probe pr, const struct blkid_idmag *mag)
 {
@@ -45,6 +76,9 @@ static int probe_apfs(blkid_probe pr, const struct blkid_idmag *mag)
 	if (!sb)
 		return errno ? -errno : BLKID_PROBE_NONE;
 
+	if (!apfs_verify_checksum(pr, sb))
+		return BLKID_PROBE_NONE;
+
 	if (le16_to_cpu(sb->type) != APFS_CONTAINER_SUPERBLOCK_TYPE)
 		return BLKID_PROBE_NONE;
 
-- 
2.33.0

