[PATCH v3] ocfs2: validate inline data i_size during inode read

[Deepanshu Kartikey <kartikey406@gmail.com>]

When reading an inode from disk, ocfs2_validate_inode_block() performs
various sanity checks but does not validate the size of inline data.
If the filesystem is corrupted, an inode's i_size can exceed the actual
inline data capacity (id_count).

This causes ocfs2_dir_foreach_blk_id() to iterate beyond the inline
data buffer, triggering a use-after-free when accessing directory
entries from freed memory.

In the syzbot report:
  - i_size was 1099511627576 bytes (~1TB)
  - Actual inline data capacity (id_count) is typically <256 bytes
  - A garbage rec_len (54648) caused ctx->pos to jump out of bounds
  - This triggered a UAF in ocfs2_check_dir_entry()

Fix by adding a validation check in ocfs2_validate_inode_block() to
ensure inodes with inline data have i_size <= id_count. This catches
the corruption early during inode read and prevents all downstream
code from operating on invalid data.

Reported-by: syzbot+c897823f699449cc3eb4@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c897823f699449cc3eb4
Tested-by: syzbot+c897823f699449cc3eb4@syzkaller.appspotmail.com
Link: https://lore.kernel.org/all/20251211115231.3560028-1-kartikey406@gmail.com/T/ [v1]
Link: https://lore.kernel.org/all/20251212040400.6377-1-kartikey406@gmail.com/T/ [v2]
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
v3:
  - Folded new check into existing OCFS2_INLINE_DATA_FL block (Joseph Qi)

v2:
  - Removed unnecessary S_ISDIR() check since OCFS2_INLINE_DATA_FL
    applies to both directories and regular files (Heming Zhao)
  - Fixed checkpatch.pl warnings
---
 fs/ocfs2/inode.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
index 8340525e5589..77f73fa663b7 100644
--- a/fs/ocfs2/inode.c
+++ b/fs/ocfs2/inode.c
@@ -1486,12 +1486,25 @@ int ocfs2_validate_inode_block(struct super_block *sb,
 		goto bail;
 	}
 
-	if ((le16_to_cpu(di->i_dyn_features) & OCFS2_INLINE_DATA_FL) &&
-	    le32_to_cpu(di->i_clusters)) {
-		rc = ocfs2_error(sb, "Invalid dinode %llu: %u clusters\n",
-				 (unsigned long long)bh->b_blocknr,
-				 le32_to_cpu(di->i_clusters));
-		goto bail;
+	if (le16_to_cpu(di->i_dyn_features) & OCFS2_INLINE_DATA_FL) {
+		struct ocfs2_inline_data *data = &di->id2.i_data;
+
+		if (le32_to_cpu(di->i_clusters)) {
+			rc = ocfs2_error(sb,
+					 "Invalid dinode %llu: %u clusters\n",
+					 (unsigned long long)bh->b_blocknr,
+					 le32_to_cpu(di->i_clusters));
+			goto bail;
+		}
+
+		if (le64_to_cpu(di->i_size) > le16_to_cpu(data->id_count)) {
+			rc = ocfs2_error(sb,
+					 "Invalid dinode #%llu: inline data i_size %llu exceeds id_count %u\n",
+					 (unsigned long long)bh->b_blocknr,
+					 (unsigned long long)le64_to_cpu(di->i_size),
+					 le16_to_cpu(data->id_count));
+			goto bail;
+		}
 	}
 
 	if (le32_to_cpu(di->i_flags) & OCFS2_CHAIN_FL) {
-- 
2.43.0