[PATCH] Fix handling of metadata_cksum

["Vladimir 'phcoder' Serbinenko" <phcoder%gmail.com@localhost>]

Current code always assumes that CG uses crc16. Yet when metadata_cksum is

enabled then it uses truncated crc32c. This patch doesn't implement full

metadata_cksum, just allows volumes with metadata_cksum to be mounted

read-only

From 75b113472849443019d55a290b4ed31dfd210d6a Mon Sep 17 00:00:00 2001
From: Vladimir Serbinenko <phcoder%gmail.com@localhost>
Date: Mon, 21 Aug 2023 23:16:12 +0200
Subject: [PATCH 2/2] ext2fs: Fix metadata_cksum

Current code always assumes that CG uses crc16. Yet when metadata_cksum is
enabled then it uses truncated crc32c. This patch doesn't implement full
metadata_cksum, just allows volumes with metadata_cksum to be mounted
read-only

---
 sys/ufs/ext2fs/ext2fs_alloc.c | 93 +++++++++++++++++++++++++++++++++++
 1 file changed, 93 insertions(+)

diff --git a/sys/ufs/ext2fs/ext2fs_alloc.c b/sys/ufs/ext2fs/ext2fs_alloc.c
index b78ba827641..7d594fb7e47 100644
--- a/sys/ufs/ext2fs/ext2fs_alloc.c
+++ b/sys/ufs/ext2fs/ext2fs_alloc.c
@@ -694,6 +694,84 @@ ext2fs_cg_update(struct m_ext2fs *fs, int cg, struct ext2_gd *gd, int nbfree, in
 		gd->ext2bgd_checksum = ext2fs_cg_get_csum(fs, cg, gd, 1 << fs->e2fs_group_desc_shift);
 }
 
+static const uint32_t ext2fs_crc32c_table[256] = {
+	0x00000000, 0xf26b8303, 0xe13b70f7, 0x1350f3f4,
+	0xc79a971f, 0x35f1141c, 0x26a1e7e8, 0xd4ca64eb,
+	0x8ad958cf, 0x78b2dbcc, 0x6be22838, 0x9989ab3b,
+	0x4d43cfd0, 0xbf284cd3, 0xac78bf27, 0x5e133c24,
+	0x105ec76f, 0xe235446c, 0xf165b798, 0x030e349b,
+	0xd7c45070, 0x25afd373, 0x36ff2087, 0xc494a384,
+	0x9a879fa0, 0x68ec1ca3, 0x7bbcef57, 0x89d76c54,
+	0x5d1d08bf, 0xaf768bbc, 0xbc267848, 0x4e4dfb4b,
+	0x20bd8ede, 0xd2d60ddd, 0xc186fe29, 0x33ed7d2a,
+	0xe72719c1, 0x154c9ac2, 0x061c6936, 0xf477ea35,
+	0xaa64d611, 0x580f5512, 0x4b5fa6e6, 0xb93425e5,
+	0x6dfe410e, 0x9f95c20d, 0x8cc531f9, 0x7eaeb2fa,
+	0x30e349b1, 0xc288cab2, 0xd1d83946, 0x23b3ba45,
+	0xf779deae, 0x05125dad, 0x1642ae59, 0xe4292d5a,
+	0xba3a117e, 0x4851927d, 0x5b016189, 0xa96ae28a,
+	0x7da08661, 0x8fcb0562, 0x9c9bf696, 0x6ef07595,
+	0x417b1dbc, 0xb3109ebf, 0xa0406d4b, 0x522bee48,
+	0x86e18aa3, 0x748a09a0, 0x67dafa54, 0x95b17957,
+	0xcba24573, 0x39c9c670, 0x2a993584, 0xd8f2b687,
+	0x0c38d26c, 0xfe53516f, 0xed03a29b, 0x1f682198,
+	0x5125dad3, 0xa34e59d0, 0xb01eaa24, 0x42752927,
+	0x96bf4dcc, 0x64d4cecf, 0x77843d3b, 0x85efbe38,
+	0xdbfc821c, 0x2997011f, 0x3ac7f2eb, 0xc8ac71e8,
+	0x1c661503, 0xee0d9600, 0xfd5d65f4, 0x0f36e6f7,
+	0x61c69362, 0x93ad1061, 0x80fde395, 0x72966096,
+	0xa65c047d, 0x5437877e, 0x4767748a, 0xb50cf789,
+	0xeb1fcbad, 0x197448ae, 0x0a24bb5a, 0xf84f3859,
+	0x2c855cb2, 0xdeeedfb1, 0xcdbe2c45, 0x3fd5af46,
+	0x7198540d, 0x83f3d70e, 0x90a324fa, 0x62c8a7f9,
+	0xb602c312, 0x44694011, 0x5739b3e5, 0xa55230e6,
+	0xfb410cc2, 0x092a8fc1, 0x1a7a7c35, 0xe811ff36,
+	0x3cdb9bdd, 0xceb018de, 0xdde0eb2a, 0x2f8b6829,
+	0x82f63b78, 0x709db87b, 0x63cd4b8f, 0x91a6c88c,
+	0x456cac67, 0xb7072f64, 0xa457dc90, 0x563c5f93,
+	0x082f63b7, 0xfa44e0b4, 0xe9141340, 0x1b7f9043,
+	0xcfb5f4a8, 0x3dde77ab, 0x2e8e845f, 0xdce5075c,
+	0x92a8fc17, 0x60c37f14, 0x73938ce0, 0x81f80fe3,
+	0x55326b08, 0xa759e80b, 0xb4091bff, 0x466298fc,
+	0x1871a4d8, 0xea1a27db, 0xf94ad42f, 0x0b21572c,
+	0xdfeb33c7, 0x2d80b0c4, 0x3ed04330, 0xccbbc033,
+	0xa24bb5a6, 0x502036a5, 0x4370c551, 0xb11b4652,
+	0x65d122b9, 0x97baa1ba, 0x84ea524e, 0x7681d14d,
+	0x2892ed69, 0xdaf96e6a, 0xc9a99d9e, 0x3bc21e9d,
+	0xef087a76, 0x1d63f975, 0x0e330a81, 0xfc588982,
+	0xb21572c9, 0x407ef1ca, 0x532e023e, 0xa145813d,
+	0x758fe5d6, 0x87e466d5, 0x94b49521, 0x66df1622,
+	0x38cc2a06, 0xcaa7a905, 0xd9f75af1, 0x2b9cd9f2,
+	0xff56bd19, 0x0d3d3e1a, 0x1e6dcdee, 0xec064eed,
+	0xc38d26c4, 0x31e6a5c7, 0x22b65633, 0xd0ddd530,
+	0x0417b1db, 0xf67c32d8, 0xe52cc12c, 0x1747422f,
+	0x49547e0b, 0xbb3ffd08, 0xa86f0efc, 0x5a048dff,
+	0x8ecee914, 0x7ca56a17, 0x6ff599e3, 0x9d9e1ae0,
+	0xd3d3e1ab, 0x21b862a8, 0x32e8915c, 0xc083125f,
+	0x144976b4, 0xe622f5b7, 0xf5720643, 0x07198540,
+	0x590ab964, 0xab613a67, 0xb831c993, 0x4a5a4a90,
+	0x9e902e7b, 0x6cfbad78, 0x7fab5e8c, 0x8dc0dd8f,
+	0xe330a81a, 0x115b2b19, 0x020bd8ed, 0xf0605bee,
+	0x24aa3f05, 0xd6c1bc06, 0xc5914ff2, 0x37faccf1,
+	0x69e9f0d5, 0x9b8273d6, 0x88d28022, 0x7ab90321,
+	0xae7367ca, 0x5c18e4c9, 0x4f48173d, 0xbd23943e,
+	0xf36e6f75, 0x0105ec76, 0x12551f82, 0xe03e9c81,
+	0x34f4f86a, 0xc69f7b69, 0xd5cf889d, 0x27a40b9e,
+	0x79b737ba, 0x8bdcb4b9, 0x988c474d, 0x6ae7c44e,
+	0xbe2da0a5, 0x4c4623a6, 0x5f16d052, 0xad7d5351,
+};
+
+static uint32_t
+ext2fs_crc32c(uint32_t last, const uint8_t *buf, size_t len)
+{
+	uint32_t crc = last;
+
+	while (len--)
+		crc = ext2fs_crc32c_table[(crc ^ *buf++) & 0xff] ^ (crc >> 8);
+
+	return crc;
+}
+
 /*
  * Compute group description csum. Structure data must be LE (not host).
  * Returned as LE (disk encoding).
@@ -705,6 +783,21 @@ ext2fs_cg_get_csum(struct m_ext2fs *fs, int cg, struct ext2_gd *gd, size_t cgsiz
 	uint32_t cg_bswapped = h2fs32((uint32_t)cg);
 	size_t off;
 
+	if (EXT2F_HAS_ROCOMPAT_FEATURE(fs, EXT2F_ROCOMPAT_METADATA_CKSUM)) {
+		uint32_t crc32;
+		uint8_t dummy[2] = {0, 0};
+
+		off = offsetof(struct ext2_gd, ext2bgd_checksum);
+
+		crc32 = ext2fs_crc32c(~0, (uint8_t *)fs->e2fs.e2fs_uuid, sizeof(fs->e2fs.e2fs_uuid));
+		crc32 = ext2fs_crc32c(crc32, (uint8_t *)&cg_bswapped, sizeof(cg_bswapped));
+		crc32 = ext2fs_crc32c(crc32, (uint8_t *)gd, off);
+		crc32 = ext2fs_crc32c(crc32, dummy, 2);
+		crc32 = ext2fs_crc32c(crc32, (uint8_t *)gd + off + 2, cgsize - (off + 2));
+
+		return h2fs16(crc32 & 0xffff);
+	}
+
 	if (!EXT2F_HAS_ROCOMPAT_FEATURE(fs, EXT2F_ROCOMPAT_GDT_CSUM))
 		return 0;
 
-- 
2.39.2