ext2/ext3/ext4: add block bitmap validation

When a new block bitmap is read from disk in read_block_bitmap() there are
a few bits that should ALWAYS be set.  In particular, the blocks given by
ext4_blk_bitmap, ext4_inode_bitmap and ext4_inode_table.  Validate the
block bitmap against these blocks.

[akpm@linux-foundation.org: cleanups]
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Andreas Dilger <adilger@clusterfs.com>
Acked-by: Mingming Cao <cmm@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 44 insertions, 12 deletions

diff --git a/fs/ext2/balloc.c b/fs/ext2/balloc.c
index 834ad4c16e2..ffaa6d84544 100644
--- a/fs/ext2/balloc.c
+++ b/fs/ext2/balloc.c
@@ -69,6 +69,14 @@ struct ext2_group_desc * ext2_get_group_desc(struct super_block * sb,
 	return desc + offset;
 }
 
+static inline int
+block_in_use(unsigned long block, struct super_block *sb, unsigned char *map)
+{
+	return ext2_test_bit ((block -
+		le32_to_cpu(EXT2_SB(sb)->s_es->s_first_data_block)) %
+			 EXT2_BLOCKS_PER_GROUP(sb), map);
+}
+
 /*
  * Read the bitmap for a given block_group, reading into the specified 
  * slot in the superblock's bitmap cache.
@@ -78,20 +86,51 @@ struct ext2_group_desc * ext2_get_group_desc(struct super_block * sb,
 static struct buffer_head *
 read_block_bitmap(struct super_block *sb, unsigned int block_group)
 {
+	int i;
 	struct ext2_group_desc * desc;
 	struct buffer_head * bh = NULL;
-	
+	unsigned int bitmap_blk;
+
 	desc = ext2_get_group_desc (sb, block_group, NULL);
 	if (!desc)
-		goto error_out;
-	bh = sb_bread(sb, le32_to_cpu(desc->bg_block_bitmap));
+		return NULL;
+	bitmap_blk = le32_to_cpu(desc->bg_block_bitmap);
+	bh = sb_bread(sb, bitmap_blk);
 	if (!bh)
-		ext2_error (sb, "read_block_bitmap",
+		ext2_error (sb, __FUNCTION__,
 			    "Cannot read block bitmap - "
 			    "block_group = %d, block_bitmap = %u",
 			    block_group, le32_to_cpu(desc->bg_block_bitmap));
-error_out:
+
+	/* check whether block bitmap block number is set */
+	if (!block_in_use(bitmap_blk, sb, bh->b_data)) {
+		/* bad block bitmap */
+		goto error_out;
+	}
+	/* check whether the inode bitmap block number is set */
+	bitmap_blk = le32_to_cpu(desc->bg_inode_bitmap);
+	if (!block_in_use(bitmap_blk, sb, bh->b_data)) {
+		/* bad block bitmap */
+		goto error_out;
+	}
+	/* check whether the inode table block number is set */
+	bitmap_blk = le32_to_cpu(desc->bg_inode_table);
+	for (i = 0; i < EXT2_SB(sb)->s_itb_per_group; i++, bitmap_blk++) {
+		if (!block_in_use(bitmap_blk, sb, bh->b_data)) {
+			/* bad block bitmap */
+			goto error_out;
+		}
+	}
+
 	return bh;
+
+error_out:
+	brelse(bh);
+	ext2_error(sb, __FUNCTION__,
+			"Invalid block bitmap - "
+			"block_group = %d, block = %u",
+			block_group, bitmap_blk);
+	return NULL;
 }
 
 /*
@@ -583,13 +622,6 @@ unsigned long ext2_count_free_blocks (struct super_block * sb)
 #endif
 }
 
-static inline int
-block_in_use(unsigned long block, struct super_block *sb, unsigned char *map)
-{
-	return ext2_test_bit ((block -
-		le32_to_cpu(EXT2_SB(sb)->s_es->s_first_data_block)) %
-			 EXT2_BLOCKS_PER_GROUP(sb), map);
-}
 
 static inline int test_root(int a, int b)
 {