Subject: Re: [PATCH bpf v2] bpf: fix null pointer deref in bpf_prog_test_run_xdp

From: Jesper Dangaard Brouer <[email-masked]>
Date: Wed, 31 Jan 2018 15:52:12 +0100

On Wed, 31 Jan 2018 12:58:56 +0100
Daniel Borkmann <[email-masked]> wrote:

> syzkaller was able to generate the following XDP program ...
> 
>   (18) r0 = 0x0
>   (61) r5 = *(u32 *)(r1 +12)
>   (04) (u32) r0 += (u32) 0
>   (95) exit
> 
> ... and trigger a NULL pointer dereference in ___bpf_prog_run()
> via bpf_prog_test_run_xdp() where this was attempted to run.
> 
> Reason is that recent xdp_rxq_info addition to XDP programs
> updated all drivers, but not bpf_prog_test_run_xdp(), where
> xdp_buff is set up. Thus when context rewriter does the deref
> on the netdev it's NULL at runtime. Fix it by using xdp_rxq
> from loopback dev. __netif_get_rx_queue() helper can also be
> reused in various other locations later on.
> 
> Fixes: 02dd3291b2f0 ("bpf: finally expose xdp_rxq_info to XDP bpf-programs")
> Reported-by: [email-masked]
> Signed-off-by: Daniel Borkmann <[email-masked]>
> Cc: Jesper Dangaard Brouer <[email-masked]>

Acked-by: Jesper Dangaard Brouer <[email-masked]>

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer