netdev - Re: [PATCH bpf-next v3 1/4] bpf_trace: check size for overflow in bpf_kprobe_multi_link

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Date:   Wed, 18 May 2022 16:30:14 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Eugene Syromiatnikov <esyr@...hat.com>
Cc:     Jiri Olsa <jolsa@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Shuah Khan <shuah@...nel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH bpf-next v3 1/4] bpf_trace: check size for overflow in bpf_kprobe_multi_link_attach

On Tue, May 17, 2022 at 12:36 AM Eugene Syromiatnikov <esyr@...hat.com> wrote:
>
> Check that size would not overflow before calculation (and return
> -EOVERFLOW if it will), to prevent potential out-of-bounds write
> with the following copy_from_user.  Use kvmalloc_array
> in copy_user_syms to prevent out-of-bounds write into syms
> (and especially buf) as well.
>
> Fixes: 0dcac272540613d4 ("bpf: Add multi kprobe link")
> Cc: <stable@...r.kernel.org> # 5.18
> Signed-off-by: Eugene Syromiatnikov <esyr@...hat.com>
> ---
>  kernel/trace/bpf_trace.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 7141ca8..9c041be 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2261,11 +2261,11 @@ static int copy_user_syms(struct user_syms *us, unsigned long __user *usyms, u32
>         int err = -ENOMEM;
>         unsigned int i;
>
> -       syms = kvmalloc(cnt * sizeof(*syms), GFP_KERNEL);
> +       syms = kvmalloc_array(cnt, sizeof(*syms), GFP_KERNEL);
>         if (!syms)
>                 goto error;
>
> -       buf = kvmalloc(cnt * KSYM_NAME_LEN, GFP_KERNEL);
> +       buf = kvmalloc_array(cnt, KSYM_NAME_LEN, GFP_KERNEL);
>         if (!buf)
>                 goto error;
>
> @@ -2461,7 +2461,8 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
>         if (!cnt)
>                 return -EINVAL;
>
> -       size = cnt * sizeof(*addrs);
> +       if (check_mul_overflow(cnt, (u32)sizeof(*addrs), &size))
> +               return -EOVERFLOW;
>         addrs = kvmalloc(size, GFP_KERNEL);

any good reason not to use kvmalloc_array() here as well and delegate
overflow to it. And then use long size (as expected by copy_from_user
anyway) everywhere?

>         if (!addrs)
>                 return -ENOMEM;
> --
> 2.1.4
>