Virtualization - Dec 2021 - [PATCH 2/2 v4] vdpa: check that offsets are within bounds

The "config.offset" comes from the user.  There needs to a check to
prevent it being out of bounds.  The "config.offset" and
"dev->config_size" variables are both type u32.  So if the offset
if
out of bounds then the "dev->config_size - config.offset"
subtraction
results in a very high u32 value.  The out of bounds offset can result
in memory corruption.

Fixes: c8a6153b6c59 ("vduse: Introduce VDUSE - vDPA Device in
Userspace")
Signed-off-by: Dan Carpenter <dan.carpenter at oracle.com>
---
v2: fix reversed if statement
v3: fix vhost_vdpa_config_validate() as pointed out by Yongji Xie.
v4: split the vhost_vdpa_config_validate() change into a separate path

 drivers/vdpa/vdpa_user/vduse_dev.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c
b/drivers/vdpa/vdpa_user/vduse_dev.c
index c9204c62f339..1a206f95d73a 100644
--- a/drivers/vdpa/vdpa_user/vduse_dev.c
+++ b/drivers/vdpa/vdpa_user/vduse_dev.c
@@ -975,7 +975,8 @@ static long vduse_dev_ioctl(struct file *file, unsigned int
cmd,
 			break;
 
 		ret = -EINVAL;
-		if (config.length == 0 ||
+		if (config.offset > dev->config_size ||
+		    config.length == 0 ||
 		    config.length > dev->config_size - config.offset)
 			break;
 
-- 
2.20.1

In this function "c->off" is a u32 and "size" is a long. 
On 64bit systems
if "c->off" is greater than "size" then "size -
c->off" is a negative and
we always return -E2BIG.  But on 32bit systems the subtraction is type
promoted to a high positive u32 value and basically any "c->len" is
accepted.

Fixes: 4c8cf31885f6 ("vhost: introduce vDPA-based backend")
Reported-by: Xie Yongji <xieyongji at bytedance.com>
Signed-off-by: Dan Carpenter <dan.carpenter at oracle.com>
---
v4: split into a separate patch

 drivers/vhost/vdpa.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index 29cced1cd277..e3c4f059b21a 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c
@@ -197,7 +197,7 @@ static int vhost_vdpa_config_validate(struct vhost_vdpa *v,
 	struct vdpa_device *vdpa = v->vdpa;
 	long size = vdpa->config->get_config_size(vdpa);
 
-	if (c->len == 0)
+	if (c->len == 0 || c->off > size)
 		return -EINVAL;
 
 	if (c->len > size - c->off)
-- 
2.20.1

On Wed, Dec 8, 2021 at 6:33 PM Dan Carpenter <dan.carpenter at oracle.com>
wrote:
>
> The "config.offset" comes from the user.  There needs to a check
to
> prevent it being out of bounds.  The "config.offset" and
> "dev->config_size" variables are both type u32.  So if the
offset if
> out of bounds then the "dev->config_size - config.offset"
subtraction
> results in a very high u32 value.  The out of bounds offset can result
> in memory corruption.
>
> Fixes: c8a6153b6c59 ("vduse: Introduce VDUSE - vDPA Device in
Userspace")
> Signed-off-by: Dan Carpenter <dan.carpenter at oracle.com>
> ---
> v2: fix reversed if statement
> v3: fix vhost_vdpa_config_validate() as pointed out by Yongji Xie.
> v4: split the vhost_vdpa_config_validate() change into a separate path
Acked-by: Jason Wang <jasowang at redhat.com>
>
>  drivers/vdpa/vdpa_user/vduse_dev.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c
b/drivers/vdpa/vdpa_user/vduse_dev.c
> index c9204c62f339..1a206f95d73a 100644
> --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> @@ -975,7 +975,8 @@ static long vduse_dev_ioctl(struct file *file, unsigned
int cmd,
>                         break;
>
>                 ret = -EINVAL;
> -               if (config.length == 0 ||
> +               if (config.offset > dev->config_size ||
> +                   config.length == 0 ||
>                     config.length > dev->config_size - config.offset)
>                         break;
>
> --
> 2.20.1
>