fix(driver): correctly retrieve src ip+port from UDP recvmsg and recvfrom

[Andreagit97]

What type of PR is this?

/kind bug

Any specific area of the project related to this PR?

/area driver-kmod

/area driver-bpf

Does this PR require a change in the driver versions?

/version driver-API-version-patch

/version driver-SCHEMA-version-patch

What this PR does / why we need it:

This PR fixes a regression in the old drivers (bpf, kmod).
Some months ago I introduced this patch Andreagit97@1bc30f3 to obtain the correct tuple from the kernel in TCP connections. Unfortunately, this broke the tuple collection with UDP connections :/ The syscall involved are recvfrom, recvmsg

TL;DR; when collecting recvfrom or recvmsg with TCP connections we shouldn't rely on userspace structs to obtain information on the tuple, we need to check it directly in the kernel because userspace structs could be empty. On the other side with UDP, we always need to check the tuple in userspace structs because IP src and port src are never written in kernel structs, the network packet directly populates userspace structs https://github.com/torvalds/linux/blob/e338142b39cf40155054f95daa28d210d2ee1b2d/net/ipv4/udp.c#L1921

The fix is quite simple. As a first attempt, we try to read IP src and port src from the kernel, if the port is invalid (0) we fall back to userspace structs. Unfortunately with UDP connections, there could be cases in which also userspace struct will be empty because maybe the user is using recvfrom with src_addr==NULL, in this case, we cannot recover IP src and port src, or at least I didn't find a reliable way to do that :(

I added some tests to check the expected output. As you can notice there are still some GTEST_SKIP(), because the behavior is not ideal, but at least we fixed the regression. In the next future, we need to adapt these network syscalls between the 3 drivers.

Which issue(s) this PR fixes:

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

fix(driver): correctly retrieve src ip+port from UDP `recvmsg` and `recvfrom`

[Andreagit97]

the fix is really small ~20 lines all the other stuff are comments and tests :)

[FedeDP]

/cc @LucaGuerra

[FedeDP]

I'd also bump driver schema minor version since this impacts what we send to userspace.

[FedeDP]

/approve

[poiana]

LGTM label has been added.

Git tree hash: 95577cb45521e1ba515a0e31189d2ee8961b465b

[Andreagit97]

I'd also bump driver schema minor version since this impacts what we send to userspace.

Done, thank you!

[LucaGuerra]

Thank you so much for this 🙏

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Andreagit97, FedeDP, LucaGuerra

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