netdev - Re: [PATCH bpf-next v5 0/9] tools: bpftool: add probes for system and device

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Date:   Tue, 22 Jan 2019 23:48:37 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Quentin Monnet <quentin.monnet@...ronome.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next v5 0/9] tools: bpftool: add probes for system and device

On Tue, Jan 22, 2019 at 10:39 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Thu, Jan 17, 2019 at 7:28 AM Quentin Monnet
> <quentin.monnet@...ronome.com> wrote:
> >
> >
> > If the user does not have root privileges (or more precisely, the
> > CAP_SYS_ADMIN capability) detection will be erroneous for most
> > parameters. Therefore, forbid non-root users to run the command.
> >
> > v5:
> > - Move exported symbols to a new LIBBPF_0.0.2 section in libbpf.map
> >   (patches 4 to 6).
> > - Minor fixes on patches 3 and 4.
>
> I was about to apply the set,
> but while testing on older kernels bpftool crashed the box.
> It's a kernel bug, no doubt, but bpftool shouldn't be doing
> dangerous operations if it can potentially crash it.
> I'm debugging what went wrong.
> It crashed after this message:
> CONFIG_XFRM is set to y
> dmesg was:
> [1757577.380114] BUG: unable to handle kernel
> [1757577.388476] NULL pointer dereference
> [1757577.395957]  at           (null)
> [1757577.402752] IP:           (null)
> [1757577.421265] Call Trace:
> [1757577.421269]  ? SyS_bpf+0x18b/0x16b0
> [1757577.421272]  ? __audit_syscall_entry+0xb5/0x100
> [1757577.421277]  do_syscall_64+0x53/0x150
> Not sure how that was possible.
> I'm still debugging.

Changed my mind and applied to bpf-next.
Turned out that one of the map types was defined in ops,
but body was not backported due to large dependencies
not suitable for backport.
That caused map_create syscall to crash.
Will send a separate fix to improve backport resilience.