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
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
v2:
  - Removed unnecessary S_ISDIR() check since OCFS2_INLINE_DATA_FL
    applies to both directories and regular files (Heming Zhao)
  - Fixed checkpatch.pl warnings
  - Updated commit message to say "inline data" instead of
    "inline directory"
---
 fs/ocfs2/inode.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
index 8340525e5589..1fac457cb04a 100644
--- a/fs/ocfs2/inode.c
+++ b/fs/ocfs2/inode.c
@@ -1521,6 +1521,23 @@ int ocfs2_validate_inode_block(struct super_block *sb,
 		}
 	}
 
+	/*
+	 * Validate inline data size. If the inode has inline data,
+	 * i_size must not exceed the inline data capacity.
+	 */
+	if (di->i_dyn_features & cpu_to_le16(OCFS2_INLINE_DATA_FL)) {
+		struct ocfs2_inline_data *data = &di->id2.i_data;
+
+		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;
+		}
+	}
+
 	rc = 0;
 
 bail:
-- 
2.43.0

On 2025/12/12 12:04, Deepanshu Kartikey wrote:
> 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
> Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
> ---
> v2:
>   - Removed unnecessary S_ISDIR() check since OCFS2_INLINE_DATA_FL
>     applies to both directories and regular files (Heming Zhao)
>   - Fixed checkpatch.pl warnings
>   - Updated commit message to say "inline data" instead of
>     "inline directory"
> ---
>  fs/ocfs2/inode.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
> index 8340525e5589..1fac457cb04a 100644
> --- a/fs/ocfs2/inode.c
> +++ b/fs/ocfs2/inode.c
> @@ -1521,6 +1521,23 @@ int ocfs2_validate_inode_block(struct super_block *sb,
>  		}
>  	}
>  
> +	/*
> +	 * Validate inline data size. If the inode has inline data,
> +	 * i_size must not exceed the inline data capacity.
> +	 */
> +	if (di->i_dyn_features & cpu_to_le16(OCFS2_INLINE_DATA_FL)) {

Since we've already have a branch to checking OCFS2_INLINE_DATA_FL, why not
fold them together?

Thanks,
Joseph

> +		struct ocfs2_inline_data *data = &di->id2.i_data;
> +
> +		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;
> +		}
> +	}
> +
>  	rc = 0;
>  
>  bail: