linux-kernel - Re: [PATCH] bpf: Replace BUG_ON when fp

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Date:   Thu, 19 Dec 2019 18:48:07 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Aditya Pakki <pakki001@....edu>, Yonghong Song <yhs@...com>
Cc:     "kjlu@....edu" <kjlu@....edu>, Alexei Starovoitov <ast@...nel.org>,
        Martin Lau <kafai@...com>, Song Liu <songliubraving@...com>,
        Andrii Nakryiko <andriin@...com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] bpf: Replace BUG_ON when fp_old is NULL

On 12/19/19 6:39 PM, Aditya Pakki wrote:
> On 12/16/19 5:17 AM, Daniel Borkmann wrote:
>> On 12/15/19 11:08 PM, Yonghong Song wrote:
>>> On 12/15/19 7:44 AM, Aditya Pakki wrote:
>>>> If fp_old is NULL in bpf_prog_realloc, the program does an assertion
>>>> and crashes. However, we can continue execution by returning NULL to
>>>> the upper callers. The patch fixes this issue.
>>>
>>> Could you share how to reproduce the assertion and crash? I would
>>> like to understand the problem first before making changes in the code.
>>> Thanks!
>>
>> Fully agree, Aditya, please elaborate if you have seen a crash!
> 
> Thanks for your responses Alexei and Daniel. We identified this issue via static analysis
> and have not seen a crash. However, by looking at the callers of bpf_prog_realloc, I do
> agree that fp_old is never NULL.
> 
> Would you recommend removing the BUG_ON assertion altogether ?

If it would ever happen, we'd already crash in fp_old->pages there, so yes,
lets remove the unneeded BUG_ON().

Thanks,
Daniel