netdev - Re: [PATHv3 net-next] bpf: enable verifier to add 0 to packet ptr

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Message-Id: <20170206.225015.897322994264531777.davem@davemloft.net>
Date:   Mon, 06 Feb 2017 22:50:15 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     u9012063@...il.com
Cc:     netdev@...r.kernel.org, mbudiu@...are.com, daniel@...earbox.net,
        ast@...nel.org
Subject: Re: [PATHv3 net-next] bpf: enable verifier to add 0 to packet ptr

From: William Tu <u9012063@...il.com>
Date: Sat,  4 Feb 2017 08:37:29 -0800

> The patch fixes the case when adding a zero value to the packet
> pointer.  The zero value could come from src_reg equals type
> BPF_K or CONST_IMM.  The patch fixes both, otherwise the verifer
> reports the following error:
>   [...]
>     R0=imm0,min_value=0,max_value=0
>     R1=pkt(id=0,off=0,r=4)
>     R2=pkt_end R3=fp-12
>     R4=imm4,min_value=4,max_value=4
>     R5=pkt(id=0,off=4,r=4)
>   269: (bf) r2 = r0     // r2 becomes imm0
>   270: (77) r2 >>= 3
>   271: (bf) r4 = r1     // r4 becomes pkt ptr
>   272: (0f) r4 += r2    // r4 += 0
>   addition of negative constant to packet pointer is not allowed
> 
> Signed-off-by: William Tu <u9012063@...il.com>
> Signed-off-by: Mihai Budiu <mbudiu@...are.com>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Acked-by: Daniel Borkmann <daniel@...earbox.net>

Applied, thanks.