TODO: handle generic_static_irregular() encoding missing

[Klaus Warnke]

TODO: in what case option_static could be set to 1 ?

I guess if a generic option do not change at all.
Maybe someone have a deeper knowledge which options
are stay unchanged due to the stream lifetime, but
I haven't. I use this, if the option it at the second
occurrence is unchanged. If it changes only once,
I use option_static == 0. There is no way back to
option_static == 1. That is, option_static == 0 is
my default value. This can be improved, if it is
well known, which options are type is static by design.

However, in test ipv4_tcp_afl54-changing-opt-ws-rnd7-2
a generic option is unchanged. To test this, I added this:

diff --git a/src/decomp/d_tcp_opts_list.c b/src/decomp/d_tcp_opts_list.c
index 0fef714..612d84b 100644
--- a/src/decomp/d_tcp_opts_list.c
+++ b/src/decomp/d_tcp_opts_list.c
@@ -1294,12 +1318,13 @@ static int d_tcp_parse_generic_irreg(const struct rohc_decomp_ctxt *const contex

  persist = &tcp_context->tcp_opts.bits[opt_index];

- /* TODO: in what case option_static could be set to 1 ? */
  if(persist->data.generic.option_static == 1)
  {
- /* TODO: handle generic_static_irregular() encoding */
- rohc_decomp_warn(context, "unsupported generic_static_irregular() encoding");
- goto error;
+ const size_t opt_load_len = persist->data.generic.load_len;
+
+ opt_ctxt->data.generic.load_len = opt_load_len;
+ memcpy(opt_ctxt->data.generic.load, persist->data.generic.load, opt_load_len);
+ rohc_decomp_debug(context, "TCP generic option payload = %zu bytes", opt_load_len);
  }
  else if(persist->data.generic.option_static == 0)
  {

The code is the same as for generic_stable_irregular.
It takes the contents from the context.
Maybe you want to extract it into a function.

Best,
Klaus Warnke

[Klaus Warnke (k-warnke)]

Hello,

this patch and the patch regarding the generic_static stuff is incomplete.
If the generic option is static, the option_static flag must be copied
around with the other fields too.
I do something like this there:

 if(persist->data.generic.option_static == 1)
 {
  opt_ctxt->data.generic = persist->data.generic;
  rohc_decomp_debug(context, "TCP generic option payload = %u bytes", persist->data.generic.load_len);
 }

instead of copy each struct element explicit. You prefer memcpy to avoid alignment issues.
Yeah, everything works on a Intel box, but if go to ARM strange things happens...
On a SPARC platform you may receive a SIGBUS, which helps.
But I assume, If there is a alignment problem, then there is a problem using
the "->" operator with this struct at all, not only when coping the whole data.
This option_static problem is the same here:

  if(discriminator == 0xff)
  {
   opt_ctxt->data.generic = persist->data.generic;
   rohc_decomp_debug(context, "TCP generic option payload = %u bytes", persist->data.generic.load_len);
  }

If no data received, the ->option_static flag must be copied too.
Or explicit:

                    const size_t opt_load_len = persist->data.generic.load_len;

                    opt_ctxt->data.generic.option_static = 0;/*persist->data.generic.option_static;*/
                    opt_ctxt->data.generic.load_len = opt_load_len;
                    memcpy(opt_ctxt->data.generic.load, persist->data.generic.load, opt_load_len);
                    rohc_decomp_debug(context, "TCP generic option payload = %zu bytes", opt_load_len);

I guess, in the case

  else if(discriminator == 0x00)
  {
...
   opt_ctxt->data.generic.option_static = 0;
   opt_ctxt->data.generic.load_len = opt_load_len;
   memcpy(opt_ctxt->data.generic.load, data + read, opt_load_len);
   read += opt_load_len;
   rohc_decomp_debug(context, "TCP generic option payload = %zu bytes", opt_load_len);

Best,
Klaus Warnke

[Klaus Warnke (k-warnke)]

Hello,

I found a real cool tool you maybe don't know.

https://wireedit.com/

I'm searching a long time for tool simply edit some bytes
in a pcap file. wireshark is not able.
There are some tools out there, but there are not
working...
So I used emcas with hexl-mode, which is pain...
To find a specific packet in a hexdump is not easy.
However WireEdit do the jobs awesome.
Adding new TCP option, checksum recalc and
automatic fixing TCP and so on.
And its free.

Best,
Klaus Warnke

[Didier Barvaux (didier-barvaux)]

Klaus,

WireEdit looks impressive. Too bad that this is not Open Source and does not run natively under Linux :-/

I used to alter PCAP with Scapy, a Python tool box to manipulate packets:
http://www.secdev.org/projects/scapy/

Regards,
Didier