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 corresponding to block bitmap, inode bitmap and inode tables.
Validate the block bitmap against these blocks.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

1 files changed, 81 insertions, 18 deletions

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index ff3428e195b4..d460223b8e1d 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -189,13 +189,65 @@ struct ext4_group_desc * ext4_get_group_desc(struct super_block * sb,
         return desc;
 }
 
+static int ext4_valid_block_bitmap(struct super_block *sb,
+                                        struct ext4_group_desc *desc,
+                                        unsigned int block_group,
+                                        struct buffer_head *bh)
+{
+        ext4_grpblk_t offset;
+        ext4_grpblk_t next_zero_bit;
+        ext4_fsblk_t bitmap_blk;
+        ext4_fsblk_t group_first_block;
+
+        if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_FLEX_BG)) {
+                /* with FLEX_BG, the inode/block bitmaps and itable
+                 * blocks may not be in the group at all
+                 * so the bitmap validation will be skipped for those groups
+                 * or it has to also read the block group where the bitmaps
+                 * are located to verify they are set.
+                 */
+                return 1;
+        }
+        group_first_block = ext4_group_first_block_no(sb, block_group);
+
+        /* check whether block bitmap block number is set */
+        bitmap_blk = ext4_block_bitmap(sb, desc);
+        offset = bitmap_blk - group_first_block;
+        if (!ext4_test_bit(offset, bh->b_data))
+                /* bad block bitmap */
+                goto err_out;
+
+        /* check whether the inode bitmap block number is set */
+        bitmap_blk = ext4_inode_bitmap(sb, desc);
+        offset = bitmap_blk - group_first_block;
+        if (!ext4_test_bit(offset, bh->b_data))
+                /* bad block bitmap */
+                goto err_out;
+
+        /* check whether the inode table block number is set */
+        bitmap_blk = ext4_inode_table(sb, desc);
+        offset = bitmap_blk - group_first_block;
+        next_zero_bit = ext4_find_next_zero_bit(bh->b_data,
+                                offset + EXT4_SB(sb)->s_itb_per_group,
+                                offset);
+        if (next_zero_bit >= offset + EXT4_SB(sb)->s_itb_per_group)
+                /* good bitmap for inode tables */
+                return 1;
+
+err_out:
+        ext4_error(sb, __FUNCTION__,
+                        "Invalid block bitmap - "
+                        "block_group = %d, block = %llu",
+                        block_group, bitmap_blk);
+        return 0;
+}
 /**
  * read_block_bitmap()
  * @sb:                 super block
  * @block_group:        given block group
  *
- * Read the bitmap for a given block_group, reading into the specified
- * slot in the superblock's bitmap cache.
+ * Read the bitmap for a given block_group,and validate the
+ * bits for block/inode/inode tables are set in the bitmaps
  *
  * Return buffer_head on success or NULL in case of failure.
  */
@@ -210,25 +262,36 @@ read_block_bitmap(struct super_block *sb, ext4_group_t block_group)
         if (!desc)
                 return NULL;
         bitmap_blk = ext4_block_bitmap(sb, desc);
+        bh = sb_getblk(sb, bitmap_blk);
+        if (unlikely(!bh)) {
+                ext4_error(sb, __FUNCTION__,
+                            "Cannot read block bitmap - "
+                            "block_group = %d, block_bitmap = %llu",
+                            (int)block_group, (unsigned long long)bitmap_blk);
+                return NULL;
+        }
+        if (bh_uptodate_or_lock(bh))
+                return bh;
+
         if (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
-                bh = sb_getblk(sb, bitmap_blk);
-                if (!buffer_uptodate(bh)) {
-                        lock_buffer(bh);
-                        if (!buffer_uptodate(bh)) {
-                                ext4_init_block_bitmap(sb, bh, block_group,
-                                                       desc);
-                                set_buffer_uptodate(bh);
-                        }
-                        unlock_buffer(bh);
-                }
-        } else {
-                bh = sb_bread(sb, bitmap_blk);
+                ext4_init_block_bitmap(sb, bh, block_group, desc);
+                set_buffer_uptodate(bh);
+                unlock_buffer(bh);
+                return bh;
         }
-        if (!bh)
-                ext4_error (sb, __FUNCTION__,
+        if (bh_submit_read(bh) < 0) {
+                put_bh(bh);
+                ext4_error(sb, __FUNCTION__,
                             "Cannot read block bitmap - "
-                            "block_group = %lu, block_bitmap = %llu",
-                            block_group, bitmap_blk);
+                            "block_group = %d, block_bitmap = %llu",
+                            (int)block_group, (unsigned long long)bitmap_blk);
+                return NULL;
+        }
+        if (!ext4_valid_block_bitmap(sb, desc, block_group, bh)) {
+                put_bh(bh);
+                return NULL;
+        }
+
         return bh;
 }
 /*