aya: Ensure that truncated map names are NULL terminated

[vadorovsky]

Limit of map names in eBPF is 16 bytes and they have to be NULL terminated.

Before this change, long names were truncated to 16 bytes. MAP_WITH_LOOOONG_NAAAAAAAAME would become MAP_WITH_LOOOONG, which doesn't contain the NULL byte.

This change fixes that by truncating the name to 15 bytes, ensuring that the 16th byte is NULL. MAP_WITH_LOOOONG_NAAAAAAAAME is truncated to MAP_WITH_LOOOON\0.

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This change is 

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[vadorovsky]

@dave-tucker @tamird this looks wild https://github.com/aya-rs/aya/actions/runs/13806711273/job/38618907343?pr=1216 given no API changes in my PR. I'll try to reproduce locally, but looks that something fishy is going on with public-api.

[vadorovsky]

nvm, I missed #1215

[dave-tucker]

Hmmm I annoyed at myself:
#1165 (comment)

I should have caught that using cmp::min would strip the nul byte 😭

Do you recall offhand if the rules are the same for program names as the logic there was changed in the same commit

[vadorovsky]

Yes, exactly the same rule applies to program names, but that was already fixed in 9eefb48:

aya/aya/src/sys/bpf.rs

Line 153 in dcf66db

let len = cmp::min(name_bytes.len(), u.prog_name.len() - 1); // Ensure NULL termination.

[tamird]

🤦

[tamird]

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @dave-tucker)

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aya/src/sys/bpf.rs line 97 at r1 (raw file):

    if KernelVersion::at_least(4, 15, 0) {
        let name_bytes = name.to_bytes();
        // u.map_name is 16 bytes max and must be NULL terminated

can we drop this comment and follow the style used below?

let len = ...; // Ensure NULL termination.

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aya/src/sys/bpf.rs line 153 at r1 (raw file):

    if let Some(name) = &aya_attr.name {
        let name_bytes = name.to_bytes();
        let len = cmp::min(name_bytes.len(), u.prog_name.len() - 1); // Ensure NULL termination.

@dave-tucker I think I fixed this after the original commit - the truncation was happening on the ingress path

9eefb48

[tamird]

🤦

[tamird]

Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @dave-tucker and @vadorovsky)

[vadorovsky]

Reviewable status: 1 of 2 files reviewed, 2 unresolved discussions (waiting on @dave-tucker and @tamird)

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aya/src/sys/bpf.rs line 97 at r1 (raw file):

Previously, tamird (Tamir Duberstein) wrote…

can we drop this comment and follow the style used below?

let len = ...; // Ensure NULL termination.

Done.

[tamird]

Reviewed 1 of 1 files at r2, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @dave-tucker)