Re: [PATCH] ocfs2: validate l_tree_depth to avoid out-of-bounds access

[Joseph Qi <joseph.qi@linux.alibaba.com>]

On 2025/2/14 03:16, Vasiliy Kovalev wrote:
> The l_tree_depth field in struct ocfs2_extent_list is defined
> as __le16, but according to the comments in the structure
> definition, the high 8 bits must not be used, meaning its
> maximum valid value is 255.
> 
> Add a check to prevent out-of-bounds access if l_tree_depth
> has an invalid value, which may occur when reading from a
> corrupted mounted disk [1].
> 
> Fixes: ccd979bdbce9 ("[PATCH] OCFS2: The Second Oracle Cluster Filesystem")
> Reported-by: syzbot+66c146268dc88f4341fd@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=66c146268dc88f4341fd [1]
> Signed-off-by: Vasiliy Kovalev <kovalev@altlinux.org>
> ---
>  fs/ocfs2/extent_map.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/fs/ocfs2/extent_map.c b/fs/ocfs2/extent_map.c
> index 930150ed5db15..0d9c25fdec029 100644
> --- a/fs/ocfs2/extent_map.c
> +++ b/fs/ocfs2/extent_map.c
> @@ -415,6 +415,15 @@ static int ocfs2_get_clusters_nocache(struct inode *inode,
>  	tree_height = le16_to_cpu(el->l_tree_depth);
>  
>  	if (tree_height > 0) {
> +		if (unlikely(tree_height > 255)) {

In fact we won't allow larger tree depth.
IIRC, it is OCFS2_MAX_PATH_DEPTH, refer ocfs2_new_path().
BTW, I'd like add this check in __ocfs2_find_path() instead.

> +			ocfs2_error(inode->i_sb,
> +				    "Inode %lu has too large l_tree_depth=%u in leaf block %llu\n",

It's not leaf, but root.

Thanks,
Joseph

> +				    inode->i_ino, tree_height,
> +				    (unsigned long long)di_bh->b_blocknr);
> +			ret = -EROFS;
> +			goto out;
> +		}
> +
>  		ret = ocfs2_find_leaf(INODE_CACHE(inode), el, v_cluster,
>  				      &eb_bh);
>  		if (ret) {