gnrc_icmpv6_echo: avoid crashing when pktbuf full

[gschorcht]

Contribution description

This PR fixes the unchecked access to (gnrc_netif_hdr_t *)hdr->data where hdr is returned from gnrc_netif_hdr_build. If packet buffer is full, gnrc_netif_hdr_build may return NULL. The following unchecked access to the pointer can then lead to a crash.

Testing procedure

Produce a lot of network traffic using ping command with maximum data size and an intervall of 0, if necessary from multiple terminals so that the packet buffer becomes full, e.g.

sudo ping6 fe80::5ecf:7fff:fe80:3f08 -Ieth0 -s1392 -i0

This test should not lead to a crash.

Issues/PRs references

Problem was found during testing PR #10862 and described in issue #10861.

[miri64]

With native this isn't really that easy to reproduce, since the TAP interface is able to handle the load quite fast (it even swallowed

for _ in $(seq 10); do sudo ping6 fe80::b41f:ceff:febe:78d3%tapbr0 -s1452 -i0 -c 100000 & done

or

for _ in $(seq 10); do sudo ping6 fe80::b41f:ceff:febe:78d3%tapbr0 -s1452 -f -c 100000 & done

mostly without problems). So I can't really test. However

[miri64]

Changes make sense ACK

[miri64]

Please provide a backport to the 2019.01-branch (You can use the script in #8968 for that if you want to).

[gschorcht]

@miri64

With native this isn't really that easy to reproduce, since the TAP interface is able to handle the load quite fast (it even swallowed ...

When bombarding examples/gnrc_networking on native using

sudo ping6 fe80::280d:21ff:fed1:c5ed -Itap0 -s1392 -i 0

in 4 terminals, it crashes with

> examples/gnrc_networking/../../Makefile.include:540: recipe for target 'term' failed
make: *** [term] segmentation violation (core dumped)

Where can I find the core file to take a look why it crashed?

[kaspar030]

Where can I find the core file to take a look why it crashed?

I had the same question for a while. On systemd systems, it is probably in /var/lib/systemd/coredump. Otherwise, /proc/sys/kernel/core_pattern might give a hint.

[kaspar030]

why it crashed

I usually compile native with CFLAGS += -g, then run it within gdb. On crash, get a backtrace with "bt".

[gschorcht]

I had the same question for a while. On systemd systems, it is probably in /var/lib/systemd/coredump. Otherwise, /proc/sys/kernel/core_pattern might give a hint.

Thanks. I'm using UNIX/Linux since 25 years, systemd is a hell. In the past it was so easy, the core file was simply created in the current directory.