[v2] udmabuf: Fix a potential (and unlikely) access to unallocated memory

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() would access to memory beyond 'list'.

Use memdup_array_user() which checks for overflow.

While at it, include <linux/string.h>.

Fixes: fbb0de795078 ("Add udmabuf misc device")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
---
v2: - Use memdup_array_user()   [Kees Cook]
    - Use sizeof(*list)   [Gustavo A. R. Silva]
    - Add include <linux/string.h>

v1: https://lore.kernel.org/all/3e37f05c7593f1016f0a46de188b3357cbbd0c0b.1695060389.git.christophe.jaillet@wanadoo.fr/

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
---
 drivers/dma-buf/udmabuf.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Le 19/02/2024 à 09:37, Dan Carpenter a écrit :
> On Sun, Feb 18, 2024 at 06:46:44PM +0100, Christophe JAILLET wrote:
>> If 'list_limit' is set to a very high value, 'lsize' computation could
>> overflow if 'head.count' is big enough.
>>
> 
> The "list_limit" is set via module parameter so if you set that high
> enough to lead to an integer overflow then you kind of deserve what
> you get.
> 
> This patch is nice for kernel hardening and making the code easier to
> read/audit but the real world security impact is negligible.

Agreed.

That is what I meant by "and unlikely".
Maybe the commit message could be more explicit if needed.

Let me know if ok as-is or if I should try to re-word the description.

CJ

> 
> regards,
> dan carpenter
> 
> 
>

On 2/18/24 11:46, 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() would access to memory beyond 'list'.
> 
> Use memdup_array_user() which checks for overflow.
> 
> While at it, include <linux/string.h>.
> 
> Fixes: fbb0de795078 ("Add udmabuf misc device")'

I don't think this tag is needed in this case.

Also, please, CC linux-hardening next time.

> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>

In any case, LGTM:

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Thanks!
--
Gustavo

> ---
> v2: - Use memdup_array_user()   [Kees Cook]
>      - Use sizeof(*list)   [Gustavo A. R. Silva]
>      - Add include <linux/string.h>
> 
> v1: https://lore.kernel.org/all/3e37f05c7593f1016f0a46de188b3357cbbd0c0b.1695060389.git.christophe.jaillet@wanadoo.fr/
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
> ---
>   drivers/dma-buf/udmabuf.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> index c40645999648..5728948ea6f2 100644
> --- a/drivers/dma-buf/udmabuf.c
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -11,6 +11,7 @@
>   #include <linux/module.h>
>   #include <linux/shmem_fs.h>
>   #include <linux/slab.h>
> +#include <linux/string.h>
>   #include <linux/udmabuf.h>
>   #include <linux/vmalloc.h>
>   #include <linux/iosys-map.h>
> @@ -314,14 +315,13 @@ 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_array_user((void __user *)(arg + sizeof(head)),
> +				 sizeof(*list), head.count);
>   	if (IS_ERR(list))
>   		return PTR_ERR(list);
>