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 834ad4c16e2d..ffaa6d845442 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)
 {