Virtualization - Dec 2021 - [PATCH v2] vduse: 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>
---
v2: version 1 had a reversed if statement

 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

On Tue, Dec 07, 2021 at 02:21:46PM +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>
> ---
> v2: version 1 had a reversed if statement
Xie Yongji pointed out that vhost_vdpa_config_validate() had a similar
issue so I'll send a v3.

regards,
dan carpenter