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

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Message-ID: <51dcca79-f819-8ebb-308e-210a0d76b1cc@umn.edu>
Date:   Thu, 19 Dec 2019 11:39:08 -0600
From:   Aditya Pakki <pakki001@....edu>
To:     Daniel Borkmann <daniel@...earbox.net>, 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 12/16/19 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 ?