linux-kernel - Re: [PATCH bpf v3 1/2] bpf_trace: check size for overflow in bpf_kprobe_multi_link

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Message-ID: <20220518200010.GA29226@asgard.redhat.com>
Date:   Wed, 18 May 2022 22:00:10 +0200
From:   Eugene Syromiatnikov <esyr@...hat.com>
To:     Yonghong Song <yhs@...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>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf v3 1/2] bpf_trace: check size for overflow in
 bpf_kprobe_multi_link_attach

On Wed, May 18, 2022 at 09:34:22AM -0700, Yonghong Song wrote:
> On 5/18/22 5:22 AM, Eugene Syromiatnikov wrote:
> >-	size = cnt * sizeof(*syms);
> >+	if (check_mul_overflow(cnt, (u32)sizeof(*syms), &size))
> >+		return -EOVERFLOW;
> 
> In mm/util.c kvmalloc_node(), we have
> 
>         /* Don't even allow crazy sizes */
>         if (unlikely(size > INT_MAX)) {
>                 WARN_ON_ONCE(!(flags & __GFP_NOWARN));
>                 return NULL;
>         }
> 
> Basically the maximum size to be allocated in INT_MAX.
> 
> Here, we have 'size' as u32, which means if the size is 0xffff0000,
> the check_mul_overflow will return false (no overflow) but
> kvzalloc will still have a warning.
> 
> I think we should change the type of 'size' to be 'int' which
> should catch the above case and be consistent with
> what kvmalloc_node() intends to warn.

Huh, it's a bitmore complicated as check_mul_overflow requires types to
match; what do you think about

+	if (check_mul_overflow(cnt, (u32)sizeof(*syms), &size) || size > INT_MAX)

?