Re: [PATCH] Fix KMSAN infoleak, initialize unused data in pskb_expand_head

[Daniel Yang]

On Thu, Oct 3, 2024 at 12:56 AM Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
>
> On Thu, Oct 3, 2024 at 6:42 AM Daniel Yang <danielyangkang@xxxxxxxxx> wrote:
> >
> > I took a look at https://www.spinics.net/lists/netdev/msg982652.html
> > and am a little confused since the patch adds a check instead of
> > initializing the memory segment.
> > Is the general assumption that any packet with uninitialized memory is
> > ill formed and we need to drop? Also is there any documentation for
> > internal macros/function calls for BPF because I was trying to look
> > and couldn't find any.
>
> Callers wanting allocated memory to be cleared use __GFP_ZERO
> If we were forcing  __GFP_ZERO all the time, network performance would
> be reduced by 30% at least.
>
> You are working around the real bug, just to silence a useful warning.
>
> As I explained earlier, the real bug is that some layers think the
> ethernet header (14 bytes) is present in the packet.
>
> Providing 14 zero bytes (instead of random bytes) would still be a bug.
>
> The real fix is to drop malicious packets when they are too small, like a NIC.

Interesting. Thank you for the clarification.