long tc program names are not truncated, causing a netlink error

[Sherlock-Holo]

when this error message reported, what is the real reason? I can't attach this https://github.com/Sherlock-Holo/mahiro/commit/fe85104164ade7fd7fec944cfb2eae2f7efbb73e#diff-b47e6e512f3e362859296f1fca2c484e0699ca24db91fcf4813a04af127701a4R20 bpf program, however, I can attach https://github.com/Sherlock-Holo/mahiro/commit/fe85104164ade7fd7fec944cfb2eae2f7efbb73e#diff-b47e6e512f3e362859296f1fca2c484e0699ca24db91fcf4813a04af127701a4R16

[Sherlock-Holo]

oh... I change #[classifier(name = "dnat_ingress_with_redirect_route")] to #[classifier(name = "dnat_ingress_with_redirect")] and it works that makes me more confused...

[dave-tucker]

I would guess the name is too long. Would be interesting where the ENOSPC comes from though. Either running with strace or Aya's debug logging enabled would be helpful.

[Sherlock-Holo]

it seems the error reported by this https://github.com/aya-rs/aya/blob/58f1ecbf0089194d729327692adca6391fc24932/aya/src/sys/netlink.rs#L491

[dave-tucker]

Ah yeah here's the issue. Name should probably be truncated here: https://github.com/aya-rs/aya/blob/58f1ecbf0089194d729327692adca6391fc24932/aya/src/sys/netlink.rs#L134

[pooladkhay]

According to the kernel code, the name can be up to 256 bytes long: https://github.com/torvalds/linux/blob/master/net/sched/cls_bpf.c#L28

#define CLS_BPF_NAME_LEN	256

And realised you have set the total length of attributes to 64 bytes: https://github.com/aya-rs/aya/blob/main/aya/src/sys/netlink.rs#L254

#[repr(C)]
struct TcRequest {
    header: nlmsghdr,
    tc_info: tcmsg,
    attrs: [u8; 64],
}

I increased the length of the attributes and it works fine until the name reaches 256 bytes limit enforced by kernel and this error appears:

Error: netlink error while attaching ebpf program to tc

Caused by:
    Invalid argument (os error 22)

So we can conclude that the limit is enforced by Aya not the kernel. Are there any particular reasons behind choosing 64 as the length of the attributes ?

[tamird]

@pooladkhay could you send a patch that increases this limit with a test? I'd be happy to guide you through writing the test.

[pooladkhay]

@pooladkhay could you send a patch that increases this limit with a test? I'd be happy to guide you through writing the test.

@tamird Yeah I'd love to do that, For the actual size, from what I saw it always requires 33 bytes for values other than name (289 bytes in total) but it just sounds like a magic number. I'll try to figure out the reason behind that 33 and if it can ever increase and will send a patch.

In the meantime I'd really appreciate it if you tell me more about the test.

[tamird]

Ah, sorry I missed your reply. The tests are in the integration-test directory. I think the smoke test is closest to what you're looking for, but have a look around. You can run these tests locally using cargo xtask integration-test -- <my-test-name>.

[tamird]

Actually, this may be the test you're looking for: https://github.com/aya-rs/aya/blob/445cb8b46318a13a94e10e11000232d4bd5b23af/test/integration-test/src/tests/load.rs#L17

[pooladkhay]

@tamird No worries, Thank you, I'll update the comment and add the test tomorrow.