[PATCH] freevxfs: reject invalid OLT record sizes

[PATCH] freevxfs: reject invalid OLT record sizes

[Sangho Lee]

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@vger.kernel.org
Signed-off-by: Sangho Lee <kudo3228@gmail.com>
---
 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);
+
+		if (rec_size < sizeof(*ocp) || rec_size > eaddr - oaddr)
+			goto fail;
 		
 		switch (fs32_to_cpu(infp, ocp->olt_type)) {
 		case VXFS_OLT_FSHEAD:
@@ -93,7 +103,11 @@
 			break;
 		}
 
-		oaddr += fs32_to_cpu(infp, ocp->olt_size);
+		/*
+		 * rec_size has already been checked to advance oaddr and stay
+		 * within the mapped OLT extent.
+		 */
+		oaddr += rec_size;
 	}
 
 	brelse(bp);
-- 
2.43.0

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@vger.kernel.org
> Signed-off-by: Sangho Lee <kudo3228@gmail.com>
> ---
>  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?

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

[Sangho Lee]

Thanks for the review.

I agree that freevxfs has extremely limited usage. My rationale was that the
filesystem remains buildable in mainline and a malformed image causes a
deterministic unbounded loop during mount. The fix is small and ensures that
the on-disk record walk always makes progress.

If you think freevxfs should no longer receive this kind of hardening, I will
not pursue the patch further. Otherwise, I can send a v2 with the line wrapped.

Thanks,
Sangho