netdev - Re: [PATCH] bpf: Replace BUG_ON when fp

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Date:   Sun, 15 Dec 2019 22:08:08 +0000
From:   Yonghong Song <yhs@...com>
To:     Aditya Pakki <pakki001@....edu>
CC:     "kjlu@....edu" <kjlu@....edu>, Alexei Starovoitov <ast@...nel.org>,
        "Daniel Borkmann" <daniel@...earbox.net>,
        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 12/15/19 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!

> 
> Signed-off-by: Aditya Pakki <pakki001@....edu>
> ---
>   kernel/bpf/core.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 49e32acad7d8..4b46654fb26b 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -222,7 +222,8 @@ struct bpf_prog *bpf_prog_realloc(struct bpf_prog *fp_old, unsigned int size,
>   	u32 pages, delta;
>   	int ret;
>   
> -	BUG_ON(fp_old == NULL);
> +	if (!fp_old)
> +		return NULL;
>   
>   	size = round_up(size, PAGE_SIZE);
>   	pages = size / PAGE_SIZE;
>