Linux Virtualization - Sep 2012 - [patch 1/3] xen/privcmd: check for integer overflow in ioctl

If m.num is too large then the "m.num * sizeof(*m.arr)" multiplication
could overflow and the access_ok() check wouldn't test the right size.

Signed-off-by: Dan Carpenter <dan.carpenter at oracle.com>
---
Only needed in linux-next.

diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index 215a3c0..fdff8f9 100644
--- a/drivers/xen/privcmd.c
+++ b/drivers/xen/privcmd.c
@@ -325,6 +325,8 @@ static long privcmd_ioctl_mmap_batch(void __user *udata, int
version)
 			return -EFAULT;
 		/* Returns per-frame error in m.arr. */
 		m.err = NULL;
+		if (m.num > SIZE_MAX / sizeof(*m.arr))
+			return -EINVAL;
 		if (!access_ok(VERIFY_WRITE, m.arr, m.num * sizeof(*m.arr)))
 			return -EFAULT;
 		break;
@@ -332,6 +334,8 @@ static long privcmd_ioctl_mmap_batch(void __user *udata, int
version)
 		if (copy_from_user(&m, udata, sizeof(struct privcmd_mmapbatch_v2)))
 			return -EFAULT;
 		/* Returns per-frame error code in m.err. */
+		if (m.num > SIZE_MAX / sizeof(*m.err))
+			return -EINVAL;
 		if (!access_ok(VERIFY_WRITE, m.err, m.num * (sizeof(*m.err))))
 			return -EFAULT;
 		break;

On Sep 8, 2012, at 5:52 AM, Dan Carpenter wrote:
> If m.num is too large then the "m.num * sizeof(*m.arr)"
multiplication
> could overflow and the access_ok() check wouldn't test the right size.
> 
> Signed-off-by: Dan Carpenter <dan.carpenter at oracle.com>
Acked-by: Andres Lagar-Cavilla <andres at
lagarcavilla.org>
> ---
> Only needed in linux-next.
> 
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index 215a3c0..fdff8f9 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -325,6 +325,8 @@ static long privcmd_ioctl_mmap_batch(void __user
*udata, int version)
> 			return -EFAULT;
> 		/* Returns per-frame error in m.arr. */
> 		m.err = NULL;
> +		if (m.num > SIZE_MAX / sizeof(*m.arr))
> +			return -EINVAL;
> 		if (!access_ok(VERIFY_WRITE, m.arr, m.num * sizeof(*m.arr)))
> 			return -EFAULT;
> 		break;
> @@ -332,6 +334,8 @@ static long privcmd_ioctl_mmap_batch(void __user
*udata, int version)
> 		if (copy_from_user(&m, udata, sizeof(struct privcmd_mmapbatch_v2)))
> 			return -EFAULT;
> 		/* Returns per-frame error code in m.err. */
> +		if (m.num > SIZE_MAX / sizeof(*m.err))
> +			return -EINVAL;
> 		if (!access_ok(VERIFY_WRITE, m.err, m.num * (sizeof(*m.err))))
> 			return -EFAULT;
> 		break;

On 08/09/12 10:52, Dan Carpenter wrote:
> If m.num is too large then the "m.num * sizeof(*m.arr)"
multiplication
> could overflow and the access_ok() check wouldn't test the right size.
m.num is range checked later on so it doesn't matter that the
access_ok() checks might be wrong.  A bit subtle, perhaps.

David
> Signed-off-by: Dan Carpenter <dan.carpenter at oracle.com>
> ---
> Only needed in linux-next.
> 
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index 215a3c0..fdff8f9 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -325,6 +325,8 @@ static long privcmd_ioctl_mmap_batch(void __user
*udata, int version)
>  			return -EFAULT;
>  		/* Returns per-frame error in m.arr. */
>  		m.err = NULL;
> +		if (m.num > SIZE_MAX / sizeof(*m.arr))
> +			return -EINVAL;
>  		if (!access_ok(VERIFY_WRITE, m.arr, m.num * sizeof(*m.arr)))
>  			return -EFAULT;
>  		break;
> @@ -332,6 +334,8 @@ static long privcmd_ioctl_mmap_batch(void __user
*udata, int version)
>  		if (copy_from_user(&m, udata, sizeof(struct privcmd_mmapbatch_v2)))
>  			return -EFAULT;
>  		/* Returns per-frame error code in m.err. */
> +		if (m.num > SIZE_MAX / sizeof(*m.err))
> +			return -EINVAL;
>  		if (!access_ok(VERIFY_WRITE, m.err, m.num * (sizeof(*m.err))))
>  			return -EFAULT;
>  		break;
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel at lists.xen.org
> http://lists.xen.org/xen-devel

On Mon, Sep 10, 2012 at 11:35:11AM +0100, David Vrabel
wrote:
> On 08/09/12 10:52, Dan Carpenter wrote:
> > If m.num is too large then the "m.num * sizeof(*m.arr)"
multiplication
> > could overflow and the access_ok() check wouldn't test the right
size.
> 
> m.num is range checked later on so it doesn't matter that the
> access_ok() checks might be wrong.  A bit subtle, perhaps.
> 
Yeah.  It's too subtle for my static checker but not so subtle for
a human being.  Laziness on my part.

Please drop this patch.

regards,
dan carpenter