Re: [PATCH bpf-next] bpf: use the proper optlen when doing strncpy in bpf_getsockopt()

From: Martin Lau <kafai@fb.com>
To: Yafang Shao <laoar.shao@gmail.com>, Lawrence Brakmo <brakmo@fb.com>
Cc: "ast@kernel.org" <ast@kernel.org>,
	"daniel@iogearbox.net" <daniel@iogearbox.net>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"shaoyafang@didiglobal.com" <shaoyafang@didiglobal.com>
Subject: Re: [PATCH bpf-next] bpf: use the proper optlen when doing strncpy in bpf_getsockopt()
Date: Tue, 22 Jan 2019 18:04:58 +0000	[thread overview]
Message-ID: <20190122180457.goq4xgtbi5cuxzwz@kafai-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <1547878852-22081-1-git-send-email-laoar.shao@gmail.com>

On Sat, Jan 19, 2019 at 02:20:52PM +0800, Yafang Shao wrote:
> As the last character of optval will be set with 0, so just copying
> (optlen - 1) characters is enough.
I am not sure this optimization is needed but I think it will
make it more consistent with the bpf_setsockopt() above.

Acked-by: Martin KaFai Lau <kafai@fb.com>

Cc: Lawrence Brakmo <brakmo@fb.com>

> 
> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> ---
>  net/core/filter.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 447dd1b..7a4de22 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -4262,7 +4262,7 @@ static unsigned long bpf_xdp_copy(void *dst_buff, const void *src_buff,
>  
>  			if (!icsk->icsk_ca_ops || optlen <= 1)
>  				goto err_clear;
> -			strncpy(optval, icsk->icsk_ca_ops->name, optlen);
> +			strncpy(optval, icsk->icsk_ca_ops->name, optlen - 1);
>  			optval[optlen - 1] = 0;
>  			break;
>  		case TCP_SAVED_SYN:
> -- 
> 1.8.3.1
>