Re: [PATCH v3 2/3] bpf: use copy_struct_from_user() in bpf_prog_get_info_by_fd()

Alexei Starovoitov
2019-10-16T05:25:56Z

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@kernel.org>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: bpf@vger.kernel.org
> Acked-by: Aleksa Sarai <cyphar@cyphar.com>
> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.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@kernel.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.