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From: Daniel Borkmann <daniel@iogearbox.net>
To: "Toke Høiland-Jørgensen" <toke@redhat.com>,
	"Yonghong Song" <yhs@fb.com>,
	ast@fb.com
Cc: bpf@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: [PATCH bpf] libbpf: Sanitise internal map names so they are not rejected by the kernel
Date: Tue, 18 Feb 2020 23:54:34 +0100	[thread overview]
Message-ID: <e7a1f042-a3d7-ad25-e195-fdd5f8b78680@iogearbox.net> (raw)
In-Reply-To: <87sgj7yhif.fsf@toke.dk>

On 2/18/20 5:42 PM, Toke Høiland-Jørgensen wrote:
> Yonghong Song <yhs@fb.com> writes:
>> On 2/18/20 6:40 AM, Daniel Borkmann wrote:
>>> On 2/17/20 6:17 PM, Toke Høiland-Jørgensen wrote:
>>>> The kernel only accepts map names with alphanumeric characters,
>>>> underscores
>>>> and periods in their name. However, the auto-generated internal map names
>>>> used by libbpf takes their prefix from the user-supplied BPF object name,
>>>> which has no such restriction. This can lead to "Invalid argument" errors
>>>> when trying to load a BPF program using global variables.
>>>>
>>>> Fix this by sanitising the map names, replacing any non-allowed
>>>> characters
>>>> with underscores.
>>>>
>>>> Fixes: d859900c4c56 ("bpf, libbpf: support global data/bss/rodata
>>>> sections")
>>>> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
>>>
>>> Makes sense to me, applied, thanks! I presume you had something like '-'
>>> in the
>>> global var leading to rejection?
>>
>> The C global variable cannot have '-'. I saw a complain in bcc mailing
>> list sometimes back like: if an object file is a-b.o, then we will
>> generate a map name like a-b.bss for the bss ELF section data. The
>> map name "a-b.bss" name will be rejected by the kernel. The workaround
>> is to change object file name. Not sure whether this is the only
>> issue which may introduce non [a-zA-Z0-9_] or not. But this patch indeed
>> should fix the issue I just described.

Yep, meant object file name, just realized too late after sending. :/

> Yes, this was exactly my problem; my object file is called
> 'xdp-dispatcher.o'. Fun error to track down :P
> 
> Why doesn't the kernel allow dashes in the name anyway?

Commit cb4d2b3f03d8 ("bpf: Add name, load_time, uid and map_ids to bpf_prog_info")
doesn't state a specific reason, and we did later extend it via 3e0ddc4f3ff1 ("bpf:
allow . char as part of the object name"). My best guess right now is potentially
not to confuse BPF's kallsyms handling with dashes etc.

  reply	other threads:[~2020-02-18 22:54 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-17 17:17 [PATCH bpf] libbpf: Sanitise internal map names so they are not rejected by the kernel Toke Høiland-Jørgensen
2020-02-18 14:40 ` Daniel Borkmann
2020-02-18 16:19   ` Yonghong Song
2020-02-18 16:42     ` Toke Høiland-Jørgensen
2020-02-18 22:54       ` Daniel Borkmann [this message]
2020-02-19 10:28         ` Toke Høiland-Jørgensen
2020-02-19 16:45           ` Yonghong Song
2020-02-19 22:29             ` Toke Høiland-Jørgensen

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