linux-kernel - Re: [PATCH 2/3] bpf: use copy_struct_from_user() in bpf_prog_get_info_by

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Date:   Thu, 10 Oct 2019 21:51:06 +1100
From:   Aleksa Sarai <cyphar@...har.com>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, bpf@...r.kernel.org,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] bpf: use copy_struct_from_user() in
 bpf_prog_get_info_by_fd()

On 2019-10-09, Christian Brauner <christian.brauner@...ntu.com> wrote:
> In v5.4-rc2 we added a new helper (cf. [1]) copy_struct_from_user().
> This helper is intended for all codepaths that copy structs from
> userspace that are versioned by size. bpf_prog_get_info_by_fd() does
> exactly what copy_struct_from_user() is doing.
> Note that copy_struct_from_user() is calling min() already. So
> technically, the min_t() call could go. But the info_len is used further
> below so leave it.
> 
> [1]: f5a1a536fa14 ("lib: introduce copy_struct_from_user() helper")
> Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>

Acked-by: Aleksa Sarai <cyphar@...har.com>

> ---
>  kernel/bpf/syscall.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 78790778f101..6f4f9097b1fe 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -2312,13 +2312,10 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog *prog,
>  	u32 ulen;
>  	int err;
>  
> -	err = bpf_check_uarg_tail_zero(uinfo, sizeof(info), info_len);
> +	info_len = min_t(u32, sizeof(info), info_len);
> +	err = copy_struct_from_user(&info, sizeof(info), uinfo, info_len);
>  	if (err)
>  		return err;
> -	info_len = min_t(u32, sizeof(info), info_len);
> -
> -	if (copy_from_user(&info, uinfo, info_len))
> -		return -EFAULT;
>  
>  	info.type = prog->type;
>  	info.id = prog->aux->id;
> -- 
> 2.23.0

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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