sys/net/grnc/netreg: avoid creating an infinite loop

[benpicco]

Contribution description

If a socket is registered twice, it's next pointer will point to itself, creating an infinite loop in _netreg_lookup() when a packet is received.

Especially when this only happens sporadically (code path that would normally close the socket is not taken) it creates a very hard to debug issue where the system is just locked up.

Instead, fail early and loud.
This would be an infinite loop on RX before, now it's a crash right at the place where the error condition occurs.

Testing procedure

Call gnrc_sock_create() on the same socket twice.
On master this will not fail, but as soon as you receive a packet on the socket, the system locks up in an infinite loop.

With this patch, the assertion will trigger on the 2nd call to gnrc_sock_create().

Issues/PRs references

[riot-ci]

Murdock results

✔️ PASSED

b7a5261 sys/net/grnc/netreg: avoid creating an infinite loop

Success	Failures	Total	Runtime
6819	0	6819	09m:34s

Artifacts

• Documentation preview

[benpicco]

bors merge

[bors]

Build succeeded:

• Murdock
• static-tests
• tools-build-success