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>

fs/ext4/balloc.c

@@ -174,6 +174,8 @@ void ext4_init_block_bitmap(struct super_block *sb, struct buffer_head *bh,
 		ext4_free_inodes_set(sb, gdp, 0);
 		ext4_itable_unused_set(sb, gdp, 0);
 		memset(bh->b_data, 0xff, sb->s_blocksize);
+		ext4_block_bitmap_csum_set(sb, block_group, gdp, bh,
+					   EXT4_BLOCKS_PER_GROUP(sb) / 8);
 		return;
 	}
 	memset(bh->b_data, 0, sb->s_blocksize);
@@ -210,6 +212,9 @@ void ext4_init_block_bitmap(struct super_block *sb, struct buffer_head *bh,
 	 */
 	ext4_mark_bitmap_end(num_clusters_in_group(sb, block_group),
 			     sb->s_blocksize * 8, bh->b_data);
+	ext4_block_bitmap_csum_set(sb, block_group, gdp, bh,
+				   EXT4_BLOCKS_PER_GROUP(sb) / 8);
+	gdp->bg_checksum = ext4_group_desc_csum(sbi, block_group, gdp);
 }
 
 /* Return the number of free blocks in a block group.  It is used when
@@ -276,9 +281,9 @@ struct ext4_group_desc * ext4_get_group_desc(struct super_block *sb,
 }
 
 static int ext4_valid_block_bitmap(struct super_block *sb,
-					struct ext4_group_desc *desc,
-					unsigned int block_group,
-					struct buffer_head *bh)
+				   struct ext4_group_desc *desc,
+				   unsigned int block_group,
+				   struct buffer_head *bh)
 {
 	ext4_grpblk_t offset;
 	ext4_grpblk_t next_zero_bit;
@@ -325,6 +330,23 @@ err_out:
 			block_group, bitmap_blk);
 	return 0;
 }
+
+void ext4_validate_block_bitmap(struct super_block *sb,
+			       struct ext4_group_desc *desc,
+			       unsigned int block_group,
+			       struct buffer_head *bh)
+{
+	if (buffer_verified(bh))
+		return;
+
+	ext4_lock_group(sb, block_group);
+	if (ext4_valid_block_bitmap(sb, desc, block_group, bh) &&
+	    ext4_block_bitmap_csum_verify(sb, block_group, desc, bh,
+					  EXT4_BLOCKS_PER_GROUP(sb) / 8))
+		set_buffer_verified(bh);
+	ext4_unlock_group(sb, block_group);
+}
+
 /**
  * ext4_read_block_bitmap()
  * @sb:			super block
@@ -355,12 +377,12 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group)
 	}
 
 	if (bitmap_uptodate(bh))
-		return bh;
+		goto verify;
 
 	lock_buffer(bh);
 	if (bitmap_uptodate(bh)) {
 		unlock_buffer(bh);
-		return bh;
+		goto verify;
 	}
 	ext4_lock_group(sb, block_group);
 	if (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
@@ -379,7 +401,7 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group)
 		 */
 		set_bitmap_uptodate(bh);
 		unlock_buffer(bh);
-		return bh;
+		goto verify;
 	}
 	/*
 	 * submit the buffer_head for reading
@@ -390,6 +412,9 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group)
 	get_bh(bh);
 	submit_bh(READ, bh);
 	return bh;
+verify:
+	ext4_validate_block_bitmap(sb, desc, block_group, bh);
+	return bh;
 }
 
 /* Returns 0 on success, 1 on error */
@@ -412,7 +437,7 @@ int ext4_wait_block_bitmap(struct super_block *sb, ext4_group_t block_group,
 	}
 	clear_buffer_new(bh);
 	/* Panic or remount fs read-only if block bitmap is invalid */
-	ext4_valid_block_bitmap(sb, desc, block_group, bh);
+	ext4_validate_block_bitmap(sb, desc, block_group, bh);
 	return 0;
 }
 

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);
+}

fs/ext4/ext4.h

@@ -1857,8 +1857,18 @@ void ext4_inode_bitmap_csum_set(struct super_block *sb, ext4_group_t group,
 int ext4_inode_bitmap_csum_verify(struct super_block *sb, ext4_group_t group,
 				  struct ext4_group_desc *gdp,
 				  struct buffer_head *bh, int sz);
+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);
+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);
 
 /* balloc.c */
+extern void ext4_validate_block_bitmap(struct super_block *sb,
+				       struct ext4_group_desc *desc,
+				       unsigned int block_group,
+				       struct buffer_head *bh);
 extern unsigned int ext4_block_group(struct super_block *sb,
 			ext4_fsblk_t blocknr);
 extern ext4_grpblk_t ext4_block_group_offset(struct super_block *sb,

fs/ext4/ialloc.c

@@ -753,6 +753,10 @@ got:
 			gdp->bg_flags &= cpu_to_le16(~EXT4_BG_BLOCK_UNINIT);
 			ext4_free_group_clusters_set(sb, gdp,
 				ext4_free_clusters_after_init(sb, group, gdp));
+			ext4_block_bitmap_csum_set(sb, group, gdp,
+						   block_bitmap_bh,
+						   EXT4_BLOCKS_PER_GROUP(sb) /
+						   8);
 			gdp->bg_checksum = ext4_group_desc_csum(sbi, group,
 								gdp);
 		}

fs/ext4/mballoc.c

@@ -788,7 +788,7 @@ static int ext4_mb_init_cache(struct page *page, char *incore)
 	int first_block;
 	struct super_block *sb;
 	struct buffer_head *bhs;
-	struct buffer_head **bh;
+	struct buffer_head **bh = NULL;
 	struct inode *inode;
 	char *data;
 	char *bitmap;
@@ -2797,6 +2797,8 @@ ext4_mb_mark_diskspace_used(struct ext4_allocation_context *ac,
 	}
 	len = ext4_free_group_clusters(sb, gdp) - ac->ac_b_ex.fe_len;
 	ext4_free_group_clusters_set(sb, gdp, len);
+	ext4_block_bitmap_csum_set(sb, ac->ac_b_ex.fe_group, gdp, bitmap_bh,
+				   EXT4_BLOCKS_PER_GROUP(sb) / 8);
 	gdp->bg_checksum = ext4_group_desc_csum(sbi, ac->ac_b_ex.fe_group, gdp);
 
 	ext4_unlock_group(sb, ac->ac_b_ex.fe_group);
@@ -4659,6 +4661,8 @@ do_more:
 
 	ret = ext4_free_group_clusters(sb, gdp) + count_clusters;
 	ext4_free_group_clusters_set(sb, gdp, ret);
+	ext4_block_bitmap_csum_set(sb, block_group, gdp, bitmap_bh,
+				   EXT4_BLOCKS_PER_GROUP(sb) / 8);
 	gdp->bg_checksum = ext4_group_desc_csum(sbi, block_group, gdp);
 	ext4_unlock_group(sb, block_group);
 	percpu_counter_add(&sbi->s_freeclusters_counter, count_clusters);
@@ -4803,6 +4807,8 @@ int ext4_group_add_blocks(handle_t *handle, struct super_block *sb,
 	mb_free_blocks(NULL, &e4b, bit, count);
 	blk_free_count = blocks_freed + ext4_free_group_clusters(sb, desc);
 	ext4_free_group_clusters_set(sb, desc, blk_free_count);
+	ext4_block_bitmap_csum_set(sb, block_group, desc, bitmap_bh,
+				   EXT4_BLOCKS_PER_GROUP(sb) / 8);
 	desc->bg_checksum = ext4_group_desc_csum(sbi, block_group, desc);
 	ext4_unlock_group(sb, block_group);
 	percpu_counter_add(&sbi->s_freeclusters_counter,

fs/ext4/resize.c

@@ -1107,6 +1107,13 @@ static int ext4_set_bitmap_checksums(struct super_block *sb,
 				   EXT4_INODES_PER_GROUP(sb) / 8);
 	brelse(bh);
 
+	bh = ext4_get_bitmap(sb, group_data->block_bitmap);
+	if (!bh)
+		return -EIO;
+	ext4_block_bitmap_csum_set(sb, group, gdp, bh,
+				   EXT4_BLOCKS_PER_GROUP(sb) / 8);
+	brelse(bh);
+
 	return 0;
 }