Virtualization - Dec 2021 - [PATCH] vduse: fix memory corruption in vduse_dev_ioctl()

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.

Fixes: c8a6153b6c59 ("vduse: Introduce VDUSE - vDPA Device in
Userspace")
Signed-off-by: Dan Carpenter <dan.carpenter at oracle.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..2f789dca0c0b 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

On Tue, Dec 07, 2021 at 01:46:14PM +0300, Dan Carpenter
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.
> 
> Fixes: c8a6153b6c59 ("vduse: Introduce VDUSE - vDPA Device in
Userspace")
> Signed-off-by: Dan Carpenter <dan.carpenter at oracle.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..2f789dca0c0b 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 ||
This is reversed.  Sorry.  Will send a fix.  I was over excited about
this patch.

Also I need to write a Smatch test for this so both the original and my
patched version generate a warning.

regards,
dan carpenter