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

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Message-ID: <5daa93e8bfc26_3a012ad7c9bb25bca6@john-XPS-13-9370.notmuch>
Date:   Fri, 18 Oct 2019 21:41:12 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        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

Alexei Starovoitov wrote:
> 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?

In this case LINUX_VERSION_CODE as shown in version.h from linux-headers
does not much what is being reported by /proc/version or osrelease.

So its a bit surprising to me as well but I haven't got to the bottom
of it. Maybe something to do with how proc is mounted in this kubernetes
setup?