sys/net/rpl: fix possible NULL dereference

[maribu]

Contribution description

As the title says

Testing procedure

No regression in RPL. (Beware: Fully untested!)

Issues/PRs references

fixes #15006 (or rather the last issue of the three instances reported there)

[riot-ci]

Murdock results

✔️ PASSED

273f92a sys/net/rpl: fix possible NULL dereference

Success	Failures	Total	Runtime
6931	0	6931	10m:26s

Artifacts

• Documentation preview

[kaspar030]

ACK. I tracked gnrc_rpl_validation_DAO_ACK() until the first access of dst without any prior NULL check.

[chrysn]

I see no user that uses this with a NULL argument, nor is it documented as optional -- is silently returning a good thing to do here? (I'd softly lean towards "passing NULL to pointer arguments that don't say they can be NULL is generally not good").

[maribu]

I think github cut of crucial context here. Just one line above the snipped shown here we have:

#ifdef MODULE_NETSTATS_RPL
    gnrc_rpl_netstats_rx_DAO_ACK(&gnrc_rpl_netstats, len, (dst && !ipv6_addr_is_multicast(dst)));
#endif

As there is already a null pointer check for dst here, I think dst being NULL indeed is indeed intended to be allowed here.

[bors]

Build failed (retrying...):

• Murdock

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

[maribu]

Thx :)