[riot-notifications] [RIOT-OS/RIOT] gnrc_ipv6_ext: don't read from `pkt->data` after `_demux()` (#11580)

Martine Lenders notifications at github.com
Fri May 24 22:10:03 CEST 2019



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### Contribution description
`_demux()` might change `pkt->data` in all kind of ways (moving it due
to `gnrc_pktbuf_mark()`, though unlikely, releasing it, because e.g. it
starts with a fragment header that marks a fragmented packet containing
only one fragment, etc.) so accessing the pointer *after* calling
`_demux()` is somewhat playing with fire. This change avoids this by
storing the value of `ext_hdr->nh` (all we are interested in here) in a
temporary variable that then is used to set the out-parameter `nh`.

`protnum` needs to be unchanged before the call to `_demux()` as it was
set by the previous iteration and determines what extension header
actually is handled.

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### Testing procedure
```sh
export BOARD="<your favorite>"
make -C tests/gnrc_ipv6_ext flash
sudo make -C tests/gnrc_ipv6_ext test
```

should still pass.
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### Issues/PRs references
None.
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You can view, comment on, or merge this pull request online at:

  https://github.com/RIOT-OS/RIOT/pull/11580

-- Commit Summary --

  * gnrc_ipv6_ext: don't read from `pkt->data` after `_demux()`

-- File Changes --

    M sys/net/gnrc/network_layer/ipv6/ext/gnrc_ipv6_ext.c (6)

-- Patch Links --

https://github.com/RIOT-OS/RIOT/pull/11580.patch
https://github.com/RIOT-OS/RIOT/pull/11580.diff

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https://github.com/RIOT-OS/RIOT/pull/11580
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