ext4: calculate and verify block bitmap checksum

Compute and verify the checksum of the block bitmap; this checksum is
stored in the block group descriptor.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 44 insertions, 0 deletions

diff --git a/fs/ext4/bitmap.c b/fs/ext4/bitmap.c
index 5813e7f2e2c6..b319721da26a 100644
--- a/fs/ext4/bitmap.c
+++ b/fs/ext4/bitmap.c
@@ -68,3 +68,47 @@ void ext4_inode_bitmap_csum_set(struct super_block *sb, ext4_group_t group,
         if (sbi->s_desc_size >= EXT4_BG_INODE_BITMAP_CSUM_HI_END)
                 gdp->bg_inode_bitmap_csum_hi = cpu_to_le16(csum >> 16);
 }
+
+int ext4_block_bitmap_csum_verify(struct super_block *sb, ext4_group_t group,
+                                  struct ext4_group_desc *gdp,
+                                  struct buffer_head *bh, int sz)
+{
+        __u32 hi;
+        __u32 provided, calculated;
+        struct ext4_sb_info *sbi = EXT4_SB(sb);
+
+        if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
+                                        EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
+                return 1;
+
+        provided = le16_to_cpu(gdp->bg_block_bitmap_csum_lo);
+        calculated = ext4_chksum(sbi, sbi->s_csum_seed, (__u8 *)bh->b_data, sz);
+        if (sbi->s_desc_size >= EXT4_BG_BLOCK_BITMAP_CSUM_HI_END) {
+                hi = le16_to_cpu(gdp->bg_block_bitmap_csum_hi);
+                provided |= (hi << 16);
+        } else
+                calculated &= 0xFFFF;
+
+        if (provided == calculated)
+                return 1;
+
+        ext4_error(sb, "Bad block bitmap checksum: block_group = %u", group);
+        return 0;
+}
+
+void ext4_block_bitmap_csum_set(struct super_block *sb, ext4_group_t group,
+                                struct ext4_group_desc *gdp,
+                                struct buffer_head *bh, int sz)
+{
+        __u32 csum;
+        struct ext4_sb_info *sbi = EXT4_SB(sb);
+
+        if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
+                        EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
+                return;
+
+        csum = ext4_chksum(sbi, sbi->s_csum_seed, (__u8 *)bh->b_data, sz);
+        gdp->bg_block_bitmap_csum_lo = cpu_to_le16(csum & 0xFFFF);
+        if (sbi->s_desc_size >= EXT4_BG_BLOCK_BITMAP_CSUM_HI_END)
+                gdp->bg_block_bitmap_csum_hi = cpu_to_le16(csum >> 16);
+}