Re: [PATCH v3 1/8] rapidio: Avoid bogus __alloc_size warning

[Gustavo A. R. Silva]

On Thu, Sep 30, 2021 at 03:26:57PM -0700, Kees Cook wrote:
> After adding __alloc_size attributes to the allocators, GCC 9.3 (but not
> later) may incorrectly evaluate the arguments to check_copy_size(),
> getting seemingly confused by the size being returned from array_size().
> Instead, perform the calculation once, which both makes the code more
> readable and avoids the bug in GCC.
> 
>    In file included from arch/x86/include/asm/preempt.h:7,
>                     from include/linux/preempt.h:78,
>                     from include/linux/spinlock.h:55,
>                     from include/linux/mm_types.h:9,
>                     from include/linux/buildid.h:5,
>                     from include/linux/module.h:14,
>                     from drivers/rapidio/devices/rio_mport_cdev.c:13:
>    In function 'check_copy_size',
>        inlined from 'copy_from_user' at include/linux/uaccess.h:191:6,
>        inlined from 'rio_mport_transfer_ioctl' at drivers/rapidio/devices/rio_mport_cdev.c:983:6:
>    include/linux/thread_info.h:213:4: error: call to '__bad_copy_to' declared with attribute error: copy destination size is too small
>      213 |    __bad_copy_to();
>          |    ^~~~~~~~~~~~~~~
> 
> But the allocation size and the copy size are identical:
> 
> 	transfer = vmalloc(array_size(sizeof(*transfer), transaction.count));
> 	if (!transfer)
> 		return -ENOMEM;
> 
> 	if (unlikely(copy_from_user(transfer,
> 				    (void __user *)(uintptr_t)transaction.block,
> 				    array_size(sizeof(*transfer), transaction.count)))) {
> 
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Link: https://lore.kernel.org/linux-mm/202109091134.FHnRmRxu-lkp@xxxxxxxxx/
> Cc: Matt Porter <mporter@xxxxxxxxxxxxxxxxxxx>
> Cc: Alexandre Bounine <alex.bou9@xxxxxxxxx>
> Cc: Jing Xiangfeng <jingxiangfeng@xxxxxxxxxx>
> Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
> Cc: Souptick Joarder <jrdr.linux@xxxxxxxxx>
> Cc: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>

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

Thanks
--
Gustavo

> ---
>  drivers/rapidio/devices/rio_mport_cdev.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/rapidio/devices/rio_mport_cdev.c b/drivers/rapidio/devices/rio_mport_cdev.c
> index 94331d999d27..7df466e22282 100644
> --- a/drivers/rapidio/devices/rio_mport_cdev.c
> +++ b/drivers/rapidio/devices/rio_mport_cdev.c
> @@ -965,6 +965,7 @@ static int rio_mport_transfer_ioctl(struct file *filp, void __user *arg)
>  	struct rio_transfer_io *transfer;
>  	enum dma_data_direction dir;
>  	int i, ret = 0;
> +	size_t size;
>  
>  	if (unlikely(copy_from_user(&transaction, arg, sizeof(transaction))))
>  		return -EFAULT;
> @@ -976,13 +977,14 @@ static int rio_mport_transfer_ioctl(struct file *filp, void __user *arg)
>  	     priv->md->properties.transfer_mode) == 0)
>  		return -ENODEV;
>  
> -	transfer = vmalloc(array_size(sizeof(*transfer), transaction.count));
> +	size = array_size(sizeof(*transfer), transaction.count);
> +	transfer = vmalloc(size);
>  	if (!transfer)
>  		return -ENOMEM;
>  
>  	if (unlikely(copy_from_user(transfer,
>  				    (void __user *)(uintptr_t)transaction.block,
> -				    array_size(sizeof(*transfer), transaction.count)))) {
> +				    size))) {
>  		ret = -EFAULT;
>  		goto out_free;
>  	}
> @@ -994,8 +996,7 @@ static int rio_mport_transfer_ioctl(struct file *filp, void __user *arg)
>  			transaction.sync, dir, &transfer[i]);
>  
>  	if (unlikely(copy_to_user((void __user *)(uintptr_t)transaction.block,
> -				  transfer,
> -				  array_size(sizeof(*transfer), transaction.count))))
> +				  transfer, size)))
>  		ret = -EFAULT;
>  
>  out_free:
> -- 
> 2.30.2
>