Re: [PATCH] udmabuf: Fix a potential (and unlikely) access to unallocated memory

[Gustavo A. R. Silva]

On 9/18/23 12:46, Christophe JAILLET wrote:
> If 'list_limit' is set to a very high value, 'lsize' computation could
> overflow if 'head.count' is big enough.
>
> In such a case, udmabuf_create() will access to memory beyond 'list'.
>
> Use size_mul() to saturate the value, and have memdup_user() fail.
>
> Fixes: fbb0de795078 ("Add udmabuf misc device")
> Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
> ---
>   drivers/dma-buf/udmabuf.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> index c40645999648..fb4c4b5b3332 100644
> --- a/drivers/dma-buf/udmabuf.c
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -314,13 +314,13 @@ static long udmabuf_ioctl_create_list(struct file *filp, unsigned long arg)
>   	struct udmabuf_create_list head;
>   	struct udmabuf_create_item *list;
>   	int ret = -EINVAL;
> -	u32 lsize;
> +	size_t lsize;
>   
>   	if (copy_from_user(&head, (void __user *)arg, sizeof(head)))
>   		return -EFAULT;
>   	if (head.count > list_limit)
>   		return -EINVAL;
> -	lsize = sizeof(struct udmabuf_create_item) * head.count;
> +	lsize = size_mul(sizeof(struct udmabuf_create_item), head.count);
>   	list = memdup_user((void __user *)(arg + sizeof(head)), lsize);
>   	if (IS_ERR(list))
>   		return PTR_ERR(list);

How about this, and we get rid of `lsize`:

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index c40645999648..5cf9d849aaa8 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -314,14 +314,13 @@ static long udmabuf_ioctl_create_list(struct file *filp, unsigned long arg)
        struct udmabuf_create_list head;
        struct udmabuf_create_item *list;
        int ret = -EINVAL;
-       u32 lsize;

        if (copy_from_user(&head, (void __user *)arg, sizeof(head)))
                return -EFAULT;
        if (head.count > list_limit)
                return -EINVAL;
-       lsize = sizeof(struct udmabuf_create_item) * head.count;
-       list = memdup_user((void __user *)(arg + sizeof(head)), lsize);
+       list = memdup_user((void __user *)(arg + sizeof(head)),
+                          size_mul(sizeof(*list), head.count));
        if (IS_ERR(list))
                return PTR_ERR(list);


--
Gustavo