On Mon, 30 Sep 2024 09:19:58 +0200,
Dan Carpenter wrote:
>
> This patch doesn't change runtime at all, it's just for kernel hardening.
>
> The "count" here comes from the user and on 32bit systems, it leads to
> integer wrapping when we pass it to compute_user_elem_size():
>
> alloc_size = compute_user_elem_size(private_size, count);
>
> However, the integer over is harmless because later "count" is checked
> when we pass it to snd_ctl_new():
>
> err = snd_ctl_new(&kctl, count, access, file);
>
> These days as part of kernel hardening we're trying to avoid integer
> overflows when they affect size_t type. So to avoid the integer overflow
> copy the check from snd_ctl_new() and do it at the start of the
> snd_ctl_elem_add() function as well.
>
> Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> ---
> I'm going to write a blog about this which explains the kernel hardening
> proposal in more detail.
>
> The problem is that integer overflows are really hard to analyze
> because the integer overflow itself is harmless. The harmful thing comes
> later. Not only are integer overflows harmless, but many of them are
> done deliberately.
>
> So what we're doing is we're saying that size_t types should not overflow.
> This eliminates many deliberate integer overflows handling time values for
> example. We're also ignoring deliberate idiomatic integer overflows such
> as if (a + b < a) {.
>
> We're going to detect these integer overflows using static analysis and at
> runtime using UBSan and Syzbot.
>
> The other thing, actually, is the we're planning to only work on 64bit
> systems for now so if you want to ignore this patch then that's fine. There
> are a lot more (like 10x more) integer overflows on 32bit systems but most
> people are on 64bit. So it's less work and more impact to focus on 64bit
> at first.
The fix is straightforward and still better to have even for 64bit, so
let's take it. Now merged to for-linus branch.
thanks,
Takashi
