netdev - Re: [bpf-next PATCH] bpf: libbpf, add kernel version section parsing back

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Date:   Fri, 18 Oct 2019 18:33:16 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Andrii Nakryiko <andriin@...com>
Cc:     John Fastabend <john.fastabend@...il.com>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>
Subject: Re: [bpf-next PATCH] bpf: libbpf, add kernel version section parsing back

On Fri, Oct 18, 2019 at 9:52 AM Andrii Nakryiko <andriin@...com> wrote:
>
> On 10/18/19 7:41 AM, John Fastabend wrote:
> > With commit "libbpf: stop enforcing kern_version,..." we removed the
> > kernel version section parsing in favor of querying for the kernel
> > using uname() and populating the version using the result of the
> > query. After this any version sections were simply ignored.
> >
> > Unfortunately, the world of kernels is not so friendly. I've found some
> > customized kernels where uname() does not match the in kernel version.
> > To fix this so programs can load in this environment this patch adds
> > back parsing the section and if it exists uses the user specified
> > kernel version to override the uname() result. However, keep most the
> > kernel uname() discovery bits so users are not required to insert the
> > version except in these odd cases.
> >
> > Fixes: 5e61f27070292 ("libbpf: stop enforcing kern_version, populate it for users")
> > Signed-off-by: John Fastabend <john.fastabend@...il.com>
> > ---
>
> In the name of not breaking users of weird kernels :)
>
> Acked-by: Andrii Nakryiko <andriin@...com>

What does it mean that uname is cheated?
Can libbpf read it from /proc/sys/kernel/osrelease ?
or /proc/version?
Is that read only or user space can somehow overwrite it?