Issue with copy_from_user() function in kernel 3.6.10

[Kristof Provost]

On 2013-07-19 21:20:07 (+0530), Sateesh Kumar <sateesh.kumar at redpinesignals.com> wrote:
>      I am declaring an array of 200 bytes as destination in ioctl 
> processing function itself even i am sending 12 bytes from application. 
> Here is the sample code how i am doing in kernel.
> 
>      ioctl_process(struct iwreq *wrq)
>      {
>          uint8 buffer[200];
>          copy_from_user(buffer, wrq->u.data.pointer, 
> wrq->u.data.length); //This line itself is causing the problem for me.
>      }
> 
I'll quote the error message you got here:

> >> "call to ‘copy_from_user_overflow’ declared with attribute warning:
> >> copy_from_user() buffer size is not provably correct"
> >>

It looks very much like you're taking a user supplied size
(wrq->u.data.length) and trusting it to be less than 200. That's bad.
Don't do that. It'll let any user panic or exploit your system.

A simple check (if wrq->u.data.length > 200 return -E2BIG;) would
probably be sufficient.

(You'll also want to check the return value of copy_from_user().)

Regards,
Kristof