netdev - Re: [PATCH bpf] bpf: use get_file_rcu() instead of get_file() for task

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Message-ID: <CAADnVQJBCWYm-CiYiJMCLVT03kquZKqdTRMJP7CmL_BWr2Cpnw@mail.gmail.com>
Date:   Mon, 17 Aug 2020 14:49:02 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Josef Bacik <josef@...icpanda.com>
Cc:     Yonghong Song <yhs@...com>, bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf] bpf: use get_file_rcu() instead of get_file() for
 task_file iterator

On Mon, Aug 17, 2020 at 11:27 AM Josef Bacik <josef@...icpanda.com> wrote:
>
> On 8/17/20 1:42 PM, Yonghong Song wrote:
> > With latest `bpftool prog` command, we observed the following kernel
> > panic.
> >      BUG: kernel NULL pointer dereference, address: 0000000000000000
> >
> > This patch used get_file_rcu() which only grabs a file if the
> > file->f_count is not zero. This is to ensure the file pointer
> > is always valid. The above reproducer did not fail for more
> > than 30 minutes.
> >
> > Fixes: eaaacd23910f ("bpf: Add task and task/file iterator targets")
> > Suggested-by: Josef Bacik <josef@...icpanda.com>
> > Signed-off-by: Yonghong Song <yhs@...com>
> > ---
>
> Reviewed-by: Josef Bacik <josef@...icpanda.com>

Applied. Thanks