Re: [PATCH] freevxfs: reject invalid OLT record sizes

[Christoph Hellwig]

On Wed, Jul 22, 2026 at 07:57:06PM +0900, Sangho Lee wrote:
> vxfs_read_olt() walks image-controlled Object Location Table records by
> adding each record's on-disk olt_size to the current cursor:
> 
> 	oaddr += fs32_to_cpu(infp, ocp->olt_size);
> 
> The value is not checked before it is used. A crafted VxFS image can set a
> record size to zero, which prevents the cursor from advancing and leaves
> mount(2) spinning in the kernel. Oversized values can also move the cursor
> past the mapped OLT block without first rejecting the malformed image.
> 
> Reject malformed OLT header and record sizes before using them. A valid
> header must place the first record after the header and within the mapped
> OLT extent. Each record must be at least large enough to contain the common
> record header and must fit in the remaining extent.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Sangho Lee <kudo3228@xxxxxxxxx>
> ---
>  fs/freevxfs/vxfs_olt.c | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/freevxfs/vxfs_olt.c b/fs/freevxfs/vxfs_olt.c
> index 23f35187c289..e5fb3b86d88e 100644
> --- a/fs/freevxfs/vxfs_olt.c
> +++ b/fs/freevxfs/vxfs_olt.c
> @@ -56,6 +56,7 @@
>  	struct buffer_head	*bp;
>  	struct vxfs_olt		*op;
>  	char			*oaddr, *eaddr;
> +	u32			olt_size;
>  
>  	bp = sb_bread(sbp, vxfs_oblock(sbp, infp->vsi_oltext, bsize));
>  	if (!bp || !bp->b_data)
> @@ -77,12 +78,21 @@
>  		goto fail;
>  	}
>  
> -	oaddr = bp->b_data + fs32_to_cpu(infp, op->olt_size);
>  	eaddr = bp->b_data + (infp->vsi_oltsize * sbp->s_blocksize);
> +	olt_size = fs32_to_cpu(infp, op->olt_size);
> +	if (olt_size < sizeof(*op) || olt_size > eaddr - bp->b_data) {
> +		pr_notice("vxfs: invalid olt header size\n");
> +		goto fail;
> +	}
> +	oaddr = bp->b_data + olt_size;
>  
>  	while (oaddr < eaddr) {
>  		struct vxfs_oltcommon	*ocp =
>  			(struct vxfs_oltcommon *)oaddr;
> +		u32			rec_size = fs32_to_cpu(infp, ocp->olt_size);

Overly long line.

Otherwise this does looks sane, but given that freevxfs had
exactly one user in the last 20 years, what is the point?