Re: [lwip-users] LWIP - mbedtls -altcp IPv4 length exceeds packet length

[Duygu D.]

Hello,

I found the problem where is;

low_level_output function was in below when I get Ipv4 error:

https://paste.ofcode.org/3afkM3cHbZTMmX7rLQuyznX

I need to change pbuf with mpbuf before the sending, so I need to copy pbuf to another mpbuf, but mpBuf length has to be p->len + 1, because I need to add data end of the datagram. 
If I use in above link I have an error. But If I use original low_level _output function like in below link:

https://paste.ofcode.org/QJhuGAjDqVsghQKqj6SyJf

I dont have any error, but I have to use first link. How can I solve the problem with copy pbuf to another pbuf ?

Best Regards.

murat palaci <askermp@hotmail.com>, 1 Eki 2021 Cum, 21:18 tarihinde şunu yazdı:

Could you try it on standard LWIP 2.0 library, for instance tcp echo server or client.. 

Murat PALACI
Electronic & Software Designer

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From: lwip-users <lwip-users-bounces+askermp=hotmail.com@nongnu.org> on behalf of Duygu D. <duygudemirpence@gmail.com>
Sent: Friday, October 1, 2021 5:31:29 PM
To: Mailing list for lwIP users <lwip-users@nongnu.org>
Subject: Re: [lwip-users] LWIP - mbedtls -altcp IPv4 length exceeds packet length

 

Hello,
After your comment I checked p->tot_len in low_level_output function and I get the 590 value but p->len = 136 byte. 
How can I solve this problem?

Best regards.

Duygu D. <duygudemirpence@gmail.com>, 1 Eki 2021 Cum, 17:13 tarihinde şunu yazdı:

And I've same problem again.

Duygu D. <duygudemirpence@gmail.com>, 1 Eki 2021 Cum, 17:12 tarihinde şunu yazdı:

Hello,

I download lwip 2.1.2 (last version) in here. Replace with my lwip files. 
And I added my lwipopt.h, and user_config.h file.

Duygu D. <duygudemirpence@gmail.com>, 1 Eki 2021 Cum, 16:36 tarihinde şunu yazdı:

Hello,

Thank you for your reply.

I couldnt find anywhere p->len is 576, I checked mbedtls's bio_send function I see 136 bytes. I dont know 576 where come from.

I am a new developper so how can I analyse this "Or your driver might be sending zero-copy but the packets get changed

between being enqueued and actually sending them" sorry for my ignorance 

Best Regards. 

goldsimon@gmx.de <goldsimon@gmx.de>, 1 Eki 2021 Cum, 15:42 tarihinde şunu yazdı:

Am 01.10.2021 um 13:40 schrieb Duygu D.:
> [..]
> When I checked the low_level_output functions I get sending data bytes
> 150 byte but Ipv4 length shows us 576 byte, opt.h file set as default
> but if I changed TCP_MSS as a 250 byte so I can send 136 byte and Ipv4
> packet lenght shows me 136. But does not make sense.  I couldnt do
> successful handshaking. Lwip takes care of the IP part if I send the
> another IP based packet (like icmp) packet with different sizes. I didnt
> get IPv4 packet length error.
> I only have this error when I used mbedtls. How can I find the problem?

One error I can think of here is that your driver might send packets
using 'p->len' instead of iterating over all pbufs ('p->tot_len',
iterate over all 'p->next').

Or your driver might be sending zero-copy but the packets get changed
between being enqueued and actually sending them?

Regards,
Simon

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