netdev - Re: [PATCH bpf-next] tools/bpf: fix a netlink recv issue

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Message-ID: <20180911212731.m3fvll4hx6qwfxj2@ast-mbp>
Date:   Tue, 11 Sep 2018 14:27:33 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Yonghong Song <yhs@...com>
Cc:     ast@...com, daniel@...earbox.net, netdev@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH bpf-next] tools/bpf: fix a netlink recv issue

On Tue, Sep 11, 2018 at 02:09:11PM -0700, Yonghong Song wrote:
> Commit f7010770fbac ("tools/bpf: move bpf/lib netlink related
> functions into a new file") introduced a while loop for the
> netlink recv path. This while loop is needed since the
> buffer in recv syscall may not be enough to hold all the
> information and in such cases multiple recv calls are needed.
> 
> There is a bug introduced by the above commit as
> the while loop may block on recv syscall if there is no
> more messages are expected. The netlink message header
> flag NLM_F_MULTI is used to indicate that more messages
> are expected and this patch fixed the bug by doing
> further recv syscall only if multipart message is expected.
> 
> The patch added another fix regarding to message length of 0.
> When netlink recv returns message length of 0, there will be
> no more messages for returning data so the while loop
> can end.
> 
> Fixes: f7010770fbac ("tools/bpf: move bpf/lib netlink related functions into a new file")
> Reported-by: Björn Töpel <bjorn.topel@...el.com>
> Tested-by: Björn Töpel <bjorn.topel@...el.com>
> Signed-off-by: Yonghong Song <yhs@...com>

Applied, Thanks