Re: [PATCH] usb: don't trust report_size for buffer size

[Németh Márton]

Kees Cook wrote:
> If the iowarrior devices in this case statement support more than 8 bytes
> per report, it is possible to write past the end of a kernel heap allocation.
> This will probably never be possible, but change the allocation to be more
> defensive anyway.

I think this might be triggered from user space, indeed. The iowarrior_class.fops->write
points directly to the function iowarrior_write(). The iowarrior_class itself
is passed to the function usb_register_dev(), which means that the write() system
call to the character device will result in calling the iowarrior_write() function.

> Signed-off-by: Kees Cook <kees.cook@xxxxxxxxxxxxx>
Acked-by: Márton Németh <nm127@xxxxxxxxxxx>

There might be similar problem also in the case USB_DEVICE_ID_CODEMERCS_IOW56. There
is buf is allocated with usb_alloc_coherent() to the size dev->report_size. However,
some lines later the copy_from_user() function tries to copy "count" number of
bytes to the dev->report_size allocated buffer. Unfortunately I don't have such
devices to try the driver so these are just coming from "static analysis".

> ---
>  drivers/usb/misc/iowarrior.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/usb/misc/iowarrior.c b/drivers/usb/misc/iowarrior.c
> index bc88c79..8ed8d05 100644
> --- a/drivers/usb/misc/iowarrior.c
> +++ b/drivers/usb/misc/iowarrior.c
> @@ -374,7 +374,7 @@ static ssize_t iowarrior_write(struct file *file,
>  	case USB_DEVICE_ID_CODEMERCS_IOWPV2:
>  	case USB_DEVICE_ID_CODEMERCS_IOW40:
>  		/* IOW24 and IOW40 use a synchronous call */
> -		buf = kmalloc(8, GFP_KERNEL);	/* 8 bytes are enough for both products */
> +		buf = kmalloc(count, GFP_KERNEL);
>  		if (!buf) {
>  			retval = -ENOMEM;
>  			goto exit;

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