netdev - Re: [PATCH v3 2/3] bpf: use copy_struct_from_user() in bpf_prog_get_info_by

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Message-ID: <20191016052548.gktf2ctvee7mrwlr@ast-mbp>
Date:   Tue, 15 Oct 2019 22:25:49 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     ast@...nel.org, bpf@...r.kernel.org, daniel@...earbox.net,
        kafai@...com, linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        songliubraving@...com, yhs@...com, Aleksa Sarai <cyphar@...har.com>
Subject: Re: [PATCH v3 2/3] bpf: use copy_struct_from_user() in
 bpf_prog_get_info_by_fd()

On Wed, Oct 16, 2019 at 05:44:31AM +0200, Christian Brauner 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")
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: bpf@...r.kernel.org
> Acked-by: Aleksa Sarai <cyphar@...har.com>
> Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
> ---
> /* v1 */
> Link: https://lore.kernel.org/r/20191009160907.10981-3-christian.brauner@ubuntu.com
> 
> /* v2 */
> Link: https://lore.kernel.org/r/20191016004138.24845-3-christian.brauner@ubuntu.com
> - Alexei Starovoitov <ast@...nel.org>:
>   - remove unneeded initialization
> 
> /* v3 */
> unchanged
> ---
>  kernel/bpf/syscall.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 40edcaeccd71..151447f314ca 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -2306,20 +2306,17 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog *prog,
>  				   union bpf_attr __user *uattr)
>  {
>  	struct bpf_prog_info __user *uinfo = u64_to_user_ptr(attr->info.info);
> -	struct bpf_prog_info info = {};
> +	struct bpf_prog_info info;
>  	u32 info_len = attr->info.info_len;
>  	struct bpf_prog_stats stats;
>  	char __user *uinsns;
>  	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);

really?! min?!
Frankly I'm disappointed in quality of these patches.
Especially considering it's v3.

Just live the code alone.