[PATCH 2/4] ocfs2: validate suballoc bit during inode read

[Joseph Qi]

i_suballoc_bit of a dinode is currently not validated at all.  A
corrupted dinode can carry an abnormally large i_suballoc_bit, which
bypasses ocfs2_validate_inode_block().  When the inode is deleted,
ocfs2_remove_inode() calls ocfs2_free_dinode(), which passes the
unvalidated bit to _ocfs2_free_suballoc_bits() and triggers
BUG_ON((count + start_bit) > ocfs2_bits_per_group(cl)).

Since suballocator block group bitmaps are contained in a single
block, a valid suballoc bit must be smaller than the number of bits
per block.  Reject oversized i_suballoc_bit values during dinode
validation.

Signed-off-by: Joseph Qi <joseph.qi@xxxxxxxxxxxxxxxxx>
---
 fs/ocfs2/inode.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
index eda50f13ffb5..a982c99a9678 100644
--- a/fs/ocfs2/inode.c
+++ b/fs/ocfs2/inode.c
@@ -1543,6 +1543,20 @@ int ocfs2_validate_inode_block(struct super_block *sb,
 		goto bail;
 	}
 
+	/*
+	 * A suballocator block group bitmap is contained in a single block,
+	 * so a valid suballoc bit can never exceed the number of bits per
+	 * block.  Otherwise deleting the inode will pass the oversized bit
+	 * to _ocfs2_free_suballoc_bits() via ocfs2_free_dinode() and trigger
+	 * BUG_ON((count + start_bit) > ocfs2_bits_per_group(cl)).
+	 */
+	if (le16_to_cpu(di->i_suballoc_bit) >= sb->s_blocksize * 8) {
+		rc = ocfs2_error(sb, "Invalid dinode %llu: suballoc bit %u\n",
+				 (unsigned long long)bh->b_blocknr,
+				 le16_to_cpu(di->i_suballoc_bit));
+		goto bail;
+	}
+
 	if ((le32_to_cpu(di->i_flags) & OCFS2_ORPHANED_FL) &&
 	    le16_to_cpu(di->i_orphaned_slot) >= OCFS2_SB(sb)->max_slots) {
 		rc = ocfs2_error(sb, "Invalid dinode %llu: orphaned slot %u\n",
-- 
2.39.3