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, 32 insertions, 7 deletions

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index 4bbd07a6fa18..0a64e4d5dbad 100644
--- a/fs/ext4/balloc.c
+++ b/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;
 }