[PATCH v2 3/3] ocfs2: reject non-inline dinodes with i_size and zero i_clusters

On a volume mounted without OCFS2_FEATURE_INCOMPAT_SPARSE_ALLOC, a
non-inline regular file with non-zero i_size and zero i_clusters is
structurally malformed: the extent map declares no allocated clusters
yet the size header claims content exists.  Keep rejecting that shape,
but express it through a shared predicate so the same invariant is
available to normal inode reads and online filecheck.

The same zero-cluster shape is also malformed for non-inline directories.
ocfs2 directory growth allocates backing storage before advancing
i_size, and ocfs2_dir_foreach_blk_el() later walks until ctx->pos reaches
i_size_read(inode).  A forged directory dinode with a huge i_size and no
clusters would repeatedly fail on holes while advancing through the
claimed size.

Sparse regular files remain exempt: on sparse-alloc volumes, truncate can
legitimately grow i_size without allocating clusters.  System inodes and
inline-data dinodes also retain their separate storage rules.

Mirror the check in ocfs2_filecheck_validate_inode_block() as well.
filecheck reports through its own error namespace, so malformed
size/cluster state is logged as a filecheck invalid-inode result rather
than via ocfs2_error(), but it must not proceed into
ocfs2_populate_inode().

Fixes: b657c95c1108 ("ocfs2: Wrap inode block reads in a dedicated function.")
Cc: [email protected]
Link: https://sashiko.dev/#/patchset/20260517111015.3187935-1-michael.bommarito%40gmail.com
Signed-off-by: Michael Bommarito <[email protected]>
Assisted-by: Claude:claude-opus-4-7
---
 fs/ocfs2/inode.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
index 992980ea98046..432eac01c1763 100644
--- a/fs/ocfs2/inode.c
+++ b/fs/ocfs2/inode.c
@@ -82,6 +82,24 @@ static bool ocfs2_dinode_has_unexpected_rdev(struct ocfs2_dinode *di)
 	return !S_ISCHR(mode) && !S_ISBLK(mode) && di->id1.dev1.i_rdev != 0;
 }
 
+static bool ocfs2_dinode_has_size_without_clusters(struct super_block *sb,
+						   struct ocfs2_dinode *di)
+{
+	umode_t mode = le16_to_cpu(di->i_mode);
+
+	if (le32_to_cpu(di->i_flags) & OCFS2_SYSTEM_FL)
+		return false;
+	if (le16_to_cpu(di->i_dyn_features) & OCFS2_INLINE_DATA_FL)
+		return false;
+	if (!le64_to_cpu(di->i_size) || le32_to_cpu(di->i_clusters))
+		return false;
+
+	if (S_ISDIR(mode))
+		return true;
+
+	return !ocfs2_sparse_alloc(OCFS2_SB(sb)) && S_ISREG(mode);
+}
+
 void ocfs2_set_inode_flags(struct inode *inode)
 {
 	unsigned int flags = OCFS2_I(inode)->ip_attr;
@@ -1563,6 +1581,33 @@ int ocfs2_validate_inode_block(struct super_block *sb,
 		goto bail;
 	}
 
+	/*
+	 * Non-inline directories must not have i_size without allocated
+	 * clusters: directory growth adds storage before advancing i_size,
+	 * and readdir walks i_size block-by-block.  A forged directory
+	 * with zero clusters and a huge i_size would repeatedly fault on
+	 * holes while advancing through the claimed size.
+	 *
+	 * Non-inline regular files have the same invariant on non-sparse
+	 * volumes.  Sparse regular files are different: truncate can
+	 * legitimately grow i_size without allocating clusters, so keep
+	 * the sparse-alloc carveout for S_IFREG only.  System inodes and
+	 * inline-data dinodes have their own storage rules.
+	 */
+	if (ocfs2_dinode_has_size_without_clusters(sb, di)) {
+		if (S_ISDIR(le16_to_cpu(di->i_mode)))
+			rc = ocfs2_error(sb,
+					 "Invalid dinode #%llu: directory i_size %llu with i_clusters 0 and no inline-data flag\n",
+					 (unsigned long long)bh->b_blocknr,
+					 (unsigned long long)le64_to_cpu(di->i_size));
+		else
+			rc = ocfs2_error(sb,
+					 "Invalid dinode #%llu: regular file i_size %llu with i_clusters 0 and no inline-data flag on non-sparse volume\n",
+					 (unsigned long long)bh->b_blocknr,
+					 (unsigned long long)le64_to_cpu(di->i_size));
+		goto bail;
+	}
+
 	if (le16_to_cpu(di->i_dyn_features) & OCFS2_INLINE_DATA_FL) {
 		struct ocfs2_inline_data *data = &di->id2.i_data;
 
@@ -1712,6 +1757,21 @@ static int ocfs2_filecheck_validate_inode_block(struct super_block *sb,
 		     le16_to_cpu(di->i_mode),
 		     (unsigned long long)le64_to_cpu(di->id1.dev1.i_rdev));
 		rc = -OCFS2_FILECHECK_ERR_INVALIDINO;
+		goto bail;
+	}
+
+	if (ocfs2_dinode_has_size_without_clusters(sb, di)) {
+		if (S_ISDIR(le16_to_cpu(di->i_mode)))
+			mlog(ML_ERROR,
+			     "Filecheck: invalid dinode #%llu: directory i_size %llu with i_clusters 0 and no inline-data flag\n",
+			     (unsigned long long)bh->b_blocknr,
+			     (unsigned long long)le64_to_cpu(di->i_size));
+		else
+			mlog(ML_ERROR,
+			     "Filecheck: invalid dinode #%llu: regular file i_size %llu with i_clusters 0 and no inline-data flag on non-sparse volume\n",
+			     (unsigned long long)bh->b_blocknr,
+			     (unsigned long long)le64_to_cpu(di->i_size));
+		rc = -OCFS2_FILECHECK_ERR_INVALIDINO;
 	}
 
 bail:
-- 
2.53.0