Re: [patch 1/2] vhost: potential integer overflows

[Dan Carpenter]

On Tue, Oct 12, 2010 at 02:25:48PM +0200, Michael S. Tsirkin wrote:
> 
> As far as I can see, maximum value for num is 64K - 1:
> 
> if (!s.num || s.num > 0x || (s.num & (s.num - 1))) {
> r = -EINVAL;
> break;
> }
> 
> How can any of the above two trigger?
> It seems easier to check value for sanity at a single place where it's
> passed from userspace to kernel.
> 

Gar.  Sorry for that.  My mistake.

regards,
dan carpenter

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Re: [patch 1/2] vhost: potential integer overflows

[Michael S. Tsirkin]

On Mon, Oct 11, 2010 at 07:22:57PM +0200, Dan Carpenter wrote:
> I did an audit for potential integer overflows of values which get passed
> to access_ok() and here are the results.
> 
> Signed-off-by: Dan Carpenter 
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index dd3d6f7..c2aa12c 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -429,6 +429,14 @@ static int vq_access_ok(unsigned int num,
>   struct vring_avail __user *avail,
>   struct vring_used __user *used)
>  {
> +
> + if (num > UINT_MAX / sizeof *desc)
> + return 0;
> + if (num > UINT_MAX / sizeof *avail->ring - sizeof *avail)
> + return 0;
> + if (num > UINT_MAX / sizeof *used->ring - sizeof *used)
> + return 0;
> +
>   return access_ok(VERIFY_READ, desc, num * sizeof *desc) &&
>  access_ok(VERIFY_READ, avail,
>sizeof *avail + num * sizeof *avail->ring) &&
> @@ -447,6 +455,9 @@ int vhost_log_access_ok(struct vhost_dev *dev)
>  /* Caller should have vq mutex and device mutex */
>  static int vq_log_access_ok(struct vhost_virtqueue *vq, void __user 
> *log_base)
>  {
> + if (vq->num > UINT_MAX / sizeof *vq->used->ring - sizeof *vq->used)
> + return 0;
> +
>   return vq_memory_access_ok(log_base, vq->dev->memory,
>   vhost_has_feature(vq->dev, VHOST_F_LOG_ALL)) &&
>   (!vq->log_used || log_access_ok(log_base, vq->log_addr,
> @@ -606,12 +617,17 @@ static long vhost_set_vring(struct vhost_dev *d, int 
> ioctl, void __user *argp)
>   }
>  
>   /* Also validate log access for used ring if enabled. */
> - if ((a.flags & (0x1 << VHOST_VRING_F_LOG)) &&
> - !log_access_ok(vq->log_base, a.log_guest_addr,
> + if (a.flags & (0x1 << VHOST_VRING_F_LOG)) {
> + if (vq->num > UINT_MAX / sizeof *vq->used->ring 
> - sizeof *vq->used) {
> + r = -EINVAL;
> + break;
> + }
> + if (!log_access_ok(vq->log_base, 
> a.log_guest_addr,
>  sizeof *vq->used +
>  vq->num * sizeof *vq->used->ring)) {
> - r = -EINVAL;
> - break;
> + r = -EINVAL;
> + break;
> + }
>   }
>   }
>  


As far as I can see, maximum value for num is 64K - 1:

if (!s.num || s.num > 0x || (s.num & (s.num - 1))) {
r = -EINVAL;
break;
}

How can any of the above two trigger?
It seems easier to check value for sanity at a single place where it's
passed from userspace to kernel.

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Re: [patch 1/2] vhost: potential integer overflows

[Al Viro]

On Mon, Oct 11, 2010 at 07:22:57PM +0200, Dan Carpenter wrote:
> I did an audit for potential integer overflows of values which get passed
> to access_ok() and here are the results.

FWIW, UINT_MAX is wrong here.  What you want is maximal size_t value.

> Signed-off-by: Dan Carpenter 
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index dd3d6f7..c2aa12c 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -429,6 +429,14 @@ static int vq_access_ok(unsigned int num,
>   struct vring_avail __user *avail,
>   struct vring_used __user *used)
>  {
> +
> + if (num > UINT_MAX / sizeof *desc)
> + return 0;
> + if (num > UINT_MAX / sizeof *avail->ring - sizeof *avail)
> + return 0;
> + if (num > UINT_MAX / sizeof *used->ring - sizeof *used)
> + return 0;
> +
>   return access_ok(VERIFY_READ, desc, num * sizeof *desc) &&
>  access_ok(VERIFY_READ, avail,
>sizeof *avail + num * sizeof *avail->ring) &&
> @@ -447,6 +455,9 @@ int vhost_log_access_ok(struct vhost_dev *dev)
>  /* Caller should have vq mutex and device mutex */
>  static int vq_log_access_ok(struct vhost_virtqueue *vq, void __user 
> *log_base)
>  {
> + if (vq->num > UINT_MAX / sizeof *vq->used->ring - sizeof *vq->used)
> + return 0;
> +
>   return vq_memory_access_ok(log_base, vq->dev->memory,
>   vhost_has_feature(vq->dev, VHOST_F_LOG_ALL)) &&
>   (!vq->log_used || log_access_ok(log_base, vq->log_addr,
> @@ -606,12 +617,17 @@ static long vhost_set_vring(struct vhost_dev *d, int 
> ioctl, void __user *argp)
>   }
>  
>   /* Also validate log access for used ring if enabled. */
> - if ((a.flags & (0x1 << VHOST_VRING_F_LOG)) &&
> - !log_access_ok(vq->log_base, a.log_guest_addr,
> + if (a.flags & (0x1 << VHOST_VRING_F_LOG)) {
> + if (vq->num > UINT_MAX / sizeof *vq->used->ring 
> - sizeof *vq->used) {
> + r = -EINVAL;
> + break;
> + }
> + if (!log_access_ok(vq->log_base, 
> a.log_guest_addr,
>  sizeof *vq->used +
>  vq->num * sizeof *vq->used->ring)) {
> - r = -EINVAL;
> - break;
> + r = -EINVAL;
> + break;
> + }
>   }
>   }
>  
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[patch 1/2] vhost: potential integer overflows

[Dan Carpenter]

I did an audit for potential integer overflows of values which get passed
to access_ok() and here are the results.

Signed-off-by: Dan Carpenter 

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index dd3d6f7..c2aa12c 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -429,6 +429,14 @@ static int vq_access_ok(unsigned int num,
struct vring_avail __user *avail,
struct vring_used __user *used)
 {
+
+   if (num > UINT_MAX / sizeof *desc)
+   return 0;
+   if (num > UINT_MAX / sizeof *avail->ring - sizeof *avail)
+   return 0;
+   if (num > UINT_MAX / sizeof *used->ring - sizeof *used)
+   return 0;
+
return access_ok(VERIFY_READ, desc, num * sizeof *desc) &&
   access_ok(VERIFY_READ, avail,
 sizeof *avail + num * sizeof *avail->ring) &&
@@ -447,6 +455,9 @@ int vhost_log_access_ok(struct vhost_dev *dev)
 /* Caller should have vq mutex and device mutex */
 static int vq_log_access_ok(struct vhost_virtqueue *vq, void __user *log_base)
 {
+   if (vq->num > UINT_MAX / sizeof *vq->used->ring - sizeof *vq->used)
+   return 0;
+
return vq_memory_access_ok(log_base, vq->dev->memory,
vhost_has_feature(vq->dev, VHOST_F_LOG_ALL)) &&
(!vq->log_used || log_access_ok(log_base, vq->log_addr,
@@ -606,12 +617,17 @@ static long vhost_set_vring(struct vhost_dev *d, int 
ioctl, void __user *argp)
}
 
/* Also validate log access for used ring if enabled. */
-   if ((a.flags & (0x1 << VHOST_VRING_F_LOG)) &&
-   !log_access_ok(vq->log_base, a.log_guest_addr,
+   if (a.flags & (0x1 << VHOST_VRING_F_LOG)) {
+   if (vq->num > UINT_MAX / sizeof *vq->used->ring 
- sizeof *vq->used) {
+   r = -EINVAL;
+   break;
+   }
+   if (!log_access_ok(vq->log_base, 
a.log_guest_addr,
   sizeof *vq->used +
   vq->num * sizeof *vq->used->ring)) {
-   r = -EINVAL;
-   break;
+   r = -EINVAL;
+   break;
+   }
}
}
 
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