netdev - Re: [PATCH v2 net-next] bpf: enable verifier to add 0 to packet ptr

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Message-ID: <5894EA90.4090807@iogearbox.net>
Date:   Fri, 03 Feb 2017 21:39:44 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     William Tu <u9012063@...il.com>
CC:     netdev@...r.kernel.org, Mihai Budiu <mbudiu@...are.com>,
        ast@...nel.org
Subject: Re: [PATCH v2 net-next] bpf: enable verifier to add 0 to packet ptr

[ please keep us Cc'ed ;) ]

On 02/03/2017 06:22 PM, William Tu wrote:
> The patch fixes the case when adding a zero value to the packet
> pointer.  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>

Acked-by: Daniel Borkmann <daniel@...earbox.net>

Thanks!