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Subject: Re: [PATCH] bpf: Replace BUG_ON when fp_old is NULL
To:     Daniel Borkmann <daniel@iogearbox.net>, Yonghong Song <yhs@fb.com>
Cc:     "kjlu@umn.edu" <kjlu@umn.edu>, Alexei Starovoitov <ast@kernel.org>,
        Martin Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
        Andrii Nakryiko <andriin@fb.com>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "bpf@vger.kernel.org" <bpf@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20191215154432.22399-1-pakki001@umn.edu>
 <98c13b9c-a73a-6203-4ea1-6b1180d87d97@fb.com>
 <566f206c-f133-6f68-c257-2c0b3ec462fa@iogearbox.net>
In-Reply-To: <566f206c-f133-6f68-c257-2c0b3ec462fa@iogearbox.net>
From:   Aditya Pakki <pakki001@umn.edu>
Message-ID: <51dcca79-f819-8ebb-308e-210a0d76b1cc@umn.edu>
Date:   Thu, 19 Dec 2019 11:39:08 -0600
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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 ?