Re: [PATCH 1/4] ocfs2: restrict OCFS2_INVALID_SLOT suballoc slot to system inodes

[Heming Zhao]

On Mon, Aug 31, 2026 at 02:28:45PM +0800, Joseph Qi wrote:
> ocfs2_validate_inode_block() currently permits i_suballoc_slot to be
> OCFS2_INVALID_SLOT for any dinode.  Only system inodes created by
> mkfs.ocfs2 are allocated from the global allocator and thus
> legitimately carry this value; regular inodes are always allocated
> from a per-slot suballocator and hence must have a valid slot.
> 
> If a corrupted regular inode with OCFS2_INVALID_SLOT is accepted,
> ocfs2_remove_inode() will pass the slot to ocfs2_get_system_file_inode()
> and get_local_system_inode() will hit BUG_ON(slot == OCFS2_INVALID_SLOT)
> when the inode is deleted.  This can be triggered by an unprivileged
> user unlinking such a corrupted file.
> 
> Reject OCFS2_INVALID_SLOT for non-system dinodes during validation,
> while still accepting it for system inodes.
> 
> Fixes: fe7a283b3916 ("ocfs2: add suballoc slot check in ocfs2_validate_inode_block()")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Joseph Qi <joseph.qi@xxxxxxxxxxxxxxxxx>

LGTM.
Reviewed-by: Heming Zhao <heming.zhao@xxxxxxxx>
> ---
>  fs/ocfs2/inode.c | 19 +++++++++++++++++--
>  1 file changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
> index 180107a11046..eda50f13ffb5 100644
> --- a/fs/ocfs2/inode.c
> +++ b/fs/ocfs2/inode.c
> @@ -1520,8 +1520,23 @@ int ocfs2_validate_inode_block(struct super_block *sb,
>  		goto bail;
>  	}
>  
> -	if (le16_to_cpu(di->i_suballoc_slot) != (u16)OCFS2_INVALID_SLOT &&
> -	    (u32)le16_to_cpu(di->i_suballoc_slot) > OCFS2_SB(sb)->max_slots - 1) {
> +	/*
> +	 * Only system inodes created by mkfs.ocfs2 are allocated from the
> +	 * global allocator and thus legitimately carry OCFS2_INVALID_SLOT.
> +	 * Regular inodes are always allocated from a per-slot suballocator.
> +	 * If a regular inode with OCFS2_INVALID_SLOT was accepted here,
> +	 * deleting it would pass the slot to get_local_system_inode() via
> +	 * ocfs2_remove_inode() and trigger BUG_ON(slot == OCFS2_INVALID_SLOT).
> +	 */
> +	if (le16_to_cpu(di->i_suballoc_slot) == (u16)OCFS2_INVALID_SLOT) {
> +		if (!(le32_to_cpu(di->i_flags) & OCFS2_SYSTEM_FL)) {
> +			rc = ocfs2_error(sb,
> +					 "Invalid dinode %llu: suballoc slot %u for non-system inode\n",
> +					 (unsigned long long)bh->b_blocknr,
> +					 le16_to_cpu(di->i_suballoc_slot));
> +			goto bail;
> +		}
> +	} else if ((u32)le16_to_cpu(di->i_suballoc_slot) > OCFS2_SB(sb)->max_slots - 1) {
>  		rc = ocfs2_error(sb, "Invalid dinode %llu: suballoc slot %u\n",
>  				 (unsigned long long)bh->b_blocknr,
>  				 le16_to_cpu(di->i_suballoc_slot));
> -- 
> 2.39.3
>