[34/37] libext2fs: Calculate and verify superblock checksums

diff --git a/lib/ext2fs/closefs.c b/lib/ext2fs/closefs.c
index 73dc136..017e9ba 100644
--- a/lib/ext2fs/closefs.c
+++ b/lib/ext2fs/closefs.c
@@ -256,10 +256,11 @@  static errcode_t write_backup_super(ext2_filsys fs, dgrp_t group,
 
 	if (sgrp > ((1 << 16) - 1))
 		sgrp = (1 << 16) - 1;
+
+	super_shadow->s_block_group_nr = sgrp;
+	ext2fs_superblock_csum_set(fs, super_shadow);
 #ifdef WORDS_BIGENDIAN
-	super_shadow->s_block_group_nr = ext2fs_swab16(sgrp);
-#else
-	fs->super->s_block_group_nr = sgrp;
+	ext2fs_swap_super(super_shadow);
 #endif
 
 	return io_channel_write_blk64(fs->io, group_block, -SUPERBLOCK_SIZE,
@@ -315,6 +316,7 @@  errcode_t ext2fs_flush(ext2_filsys fs)
 				  &group_shadow);
 	if (retval)
 		goto errout;
+	memcpy(super_shadow, fs->super, sizeof(struct ext2_super_block));
 	memcpy(group_shadow, fs->group_desc, (size_t) fs->blocksize *
 	       fs->desc_blocks);
 
@@ -335,10 +337,6 @@  errcode_t ext2fs_flush(ext2_filsys fs)
 	 */
 	fs->super->s_state &= ~EXT2_VALID_FS;
 	fs->super->s_feature_incompat &= ~EXT3_FEATURE_INCOMPAT_RECOVER;
-#ifdef WORDS_BIGENDIAN
-	*super_shadow = *fs->super;
-	ext2fs_swap_super(super_shadow);
-#endif
 
 	/*
 	 * If this is an external journal device, don't write out the
@@ -408,6 +406,7 @@  write_primary_superblock_only:
 	fs->super->s_block_group_nr = 0;
 	fs->super->s_state = fs_state;
 	fs->super->s_feature_incompat = feature_incompat;
+	ext2fs_superblock_csum_set(fs, fs->super);
 #ifdef WORDS_BIGENDIAN
 	*super_shadow = *fs->super;
 	ext2fs_swap_super(super_shadow);
diff --git a/lib/ext2fs/csum.c b/lib/ext2fs/csum.c
index dc87de3..1da5bfc 100644
--- a/lib/ext2fs/csum.c
+++ b/lib/ext2fs/csum.c
@@ -29,6 +29,45 @@ 
 #define STATIC static
 #endif
 
+__u32 ext2fs_superblock_csum(ext2_filsys fs, struct ext2_super_block *sb)
+{
+	int offset = offsetof(struct ext2_super_block, s_checksum);
+	__u32 crc = 0;
+
+	if (!EXT2_HAS_RO_COMPAT_FEATURE(fs->super,
+					EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
+		return 0;
+
+#ifdef WORDS_BIGENDIAN
+	struct ext2_super_block swabsb;
+	memcpy(&swabsb, sb, sizeof(struct ext2_super_block));
+	ext2fs_swap_super(&swabsb);
+	sb = &swabsb;
+#endif
+
+	crc = crc32c_le(~0, (char *)sb, offset);
+
+	return crc;
+}
+
+int ext2fs_superblock_csum_verify(ext2_filsys fs, struct ext2_super_block *sb)
+{
+	if (EXT2_HAS_RO_COMPAT_FEATURE(fs->super,
+				       EXT4_FEATURE_RO_COMPAT_METADATA_CSUM) &&
+	    (sb->s_checksum != ext2fs_superblock_csum(fs, sb)))
+		return 0;
+	return 1;
+}
+
+void ext2fs_superblock_csum_set(ext2_filsys fs, struct ext2_super_block *sb)
+{
+	if (!EXT2_HAS_RO_COMPAT_FEATURE(fs->super,
+		EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
+		return;
+
+	sb->s_checksum = ext2fs_superblock_csum(fs, sb);
+}
+
 __u32 ext2fs_ext_attr_block_csum(ext2_filsys fs, blk64_t block,
 				 struct ext2_ext_attr_header *hdr)
 {
diff --git a/lib/ext2fs/ext2_err.et.in b/lib/ext2fs/ext2_err.et.in
index 6e2c22c..956427d 100644
--- a/lib/ext2fs/ext2_err.et.in
+++ b/lib/ext2fs/ext2_err.et.in
@@ -434,4 +434,7 @@  ec	EXT2_ET_INODE_CSUM_NONZERO,
 ec	EXT2_ET_EXT_ATTR_BLOCK_CORRUPT,
 	"Extended attribute block fails checksum"
 
+ec	EXT2_ET_SB_CSUM_INVALID,
+	"Superblock fails checksum"
+
 	end
diff --git a/lib/ext2fs/ext2_fs.h b/lib/ext2fs/ext2_fs.h
index 40b5900..7d43e15 100644
--- a/lib/ext2fs/ext2_fs.h
+++ b/lib/ext2fs/ext2_fs.h
@@ -589,7 +589,8 @@  struct ext2_super_block {
 	__u32	s_usr_quota_inum;	/* inode number of user quota file */
 	__u32	s_grp_quota_inum;	/* inode number of group quota file */
 	__u32	s_overhead_blocks;	/* overhead blocks/clusters in fs */
-	__u32   s_reserved[109];        /* Padding to the end of the block */
+	__u32	s_checksum;		/* crc32c(superblock) */
+	__u32   s_reserved[108];        /* Padding to the end of the block */
 };
 
 #define EXT4_S_ERR_LEN (EXT4_S_ERR_END - EXT4_S_ERR_START)
diff --git a/lib/ext2fs/ext2fs.h b/lib/ext2fs/ext2fs.h
index 0820e43..282806b 100644
--- a/lib/ext2fs/ext2fs.h
+++ b/lib/ext2fs/ext2fs.h
@@ -894,6 +894,12 @@  extern __u32 crc32c_be(__u32 crc, unsigned char const *p, size_t len);
 extern __u32 crc32c_le(__u32 crc, unsigned char const *p, size_t len);
 
 /* csum.c */
+extern __u32 ext2fs_superblock_csum(ext2_filsys fs,
+				    struct ext2_super_block *sb);
+extern int ext2fs_superblock_csum_verify(ext2_filsys fs,
+					 struct ext2_super_block *sb);
+extern void ext2fs_superblock_csum_set(ext2_filsys fs,
+				       struct ext2_super_block *sb);
 extern __u32 ext2fs_ext_attr_block_csum(ext2_filsys fs, blk64_t block,
 					struct ext2_ext_attr_header *hdr);
 extern int ext2fs_ext_attr_block_csum_verify(ext2_filsys fs, blk64_t block,
diff --git a/lib/ext2fs/openfs.c b/lib/ext2fs/openfs.c
index 0edeb2f..5472d9a 100644
--- a/lib/ext2fs/openfs.c
+++ b/lib/ext2fs/openfs.c
@@ -198,6 +198,12 @@  errcode_t ext2fs_open2(const char *name, const char *io_options,
 	}
 #endif
 
+	if (!(fs->flags & EXT2_FLAG_IGNORE_CSUM_ERRORS) &&
+	    !ext2fs_superblock_csum_verify(fs, fs->super)) {
+		retval = EXT2_ET_SB_CSUM_INVALID;
+		goto cleanup;
+	}
+
 	if (fs->super->s_magic != EXT2_SUPER_MAGIC) {
 		retval = EXT2_ET_BAD_MAGIC;
 		goto cleanup;
diff --git a/lib/ext2fs/swapfs.c b/lib/ext2fs/swapfs.c
index 5cbb4b9..5234451 100644
--- a/lib/ext2fs/swapfs.c
+++ b/lib/ext2fs/swapfs.c
@@ -94,6 +94,8 @@  void ext2fs_swap_super(struct ext2_super_block * sb)
 	}
 	for (; i < 17; i++)
 		sb->s_jnl_blocks[i] = ext2fs_swab32(sb->s_jnl_blocks[i]);
+
+	sb->s_checksum = ext2fs_swab32(sb->s_checksum);
 }
 
 void ext2fs_swap_group_desc2(ext2_filsys fs, struct ext2_group_desc *gdp)