Re: [lwip-users] wrong checksum on some ICMP echo replies

[Sylvain Rochet]

Hello Fabian,

On Wed, Jun 10, 2015 at 10:57:35AM +0000, Fabian Koch wrote:
> Hey all,
> 
> I found a bug in icmp.c for IPv4 in LWIP 1.4.1 (but it is also present in git 
> master):
> 
> When a client sends an ICMP echo request with ID 0, Sequence 0 and either no 
> data or any amount of 0x00 Bytes as data, the checksum in the reply by LWIP 
> is wrong (off-by-one).
> 
> Expected checksum is 0xffff in that case, observed is 0x0000.
> So the client does not see that reply as valid and determines the LWIP device 
> as unreachable.
> Most "usual" ping applications do send a payload that is not only NULL bytes, 
> so this probably slipped by ;o)
> 
> I opened an issue on my github fork of LWIP and fixed it there:
> https://github.com/tabascoeye/lwip/issues/17
> https://github.com/tabascoeye/lwip/commit/32c32d8e2681e1f456ad487ac9f4159f7e765d57
> 
> do you guys agree on this fix?

Applied, thanks.

Sylvain

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