netdev - Re: [PATCH bpf v2 1/4] bpf_trace: check size for overflow in bpf_kprobe_multi_link

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Date:   Tue, 17 May 2022 00:01:32 -0700
From:   Yonghong Song <yhs@...com>
To:     Eugene Syromiatnikov <esyr@...hat.com>,
        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>
Cc:     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,
        Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf v2 1/4] bpf_trace: check size for overflow in
 bpf_kprobe_multi_link_attach



On 5/16/22 4:04 PM, Eugene Syromiatnikov 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.  Add the same check
> to kprobe_multi_resolve_syms in case it will be called from elsewhere
> in the future.
> 
> Fixes: 0dcac272540613d4 ("bpf: Add multi kprobe link")
> Signed-off-by: Eugene Syromiatnikov <esyr@...hat.com>
> ---
>   kernel/trace/bpf_trace.c | 11 ++++++++---
>   1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index d8553f4..f1d4e68 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2352,12 +2352,15 @@ static int
>   kprobe_multi_resolve_syms(const void __user *usyms, u32 cnt,
>   			  unsigned long *addrs)
>   {
> -	unsigned long addr, size;
> +	unsigned long addr, sym_size;
> +	u32 size;
>   	const char __user **syms;
>   	int err = -ENOMEM;
>   	unsigned int i;
>   	char *func;
>   
> +	if (check_mul_overflow(cnt, (u32)sizeof(*syms), &size))
> +		return -EOVERFLOW;
>   	size = cnt * sizeof(*syms);

The statement 'size = cnt * sizeof(*syms)' can be removed right?
Here, the 'size' will be computed properly with check_mul_overflow()
if 0 is returned.

>   	syms = kvzalloc(size, GFP_KERNEL);
>   	if (!syms)
> @@ -2382,9 +2385,9 @@ kprobe_multi_resolve_syms(const void __user *usyms, u32 cnt,
>   		addr = kallsyms_lookup_name(func);
>   		if (!addr)
>   			goto error;
> -		if (!kallsyms_lookup_size_offset(addr, &size, NULL))
> +		if (!kallsyms_lookup_size_offset(addr, &sym_size, NULL))
>   			goto error;
> -		addr = ftrace_location_range(addr, addr + size - 1);
> +		addr = ftrace_location_range(addr, addr + sym_size - 1);
>   		if (!addr)
>   			goto error;
>   		addrs[i] = addr;
> @@ -2429,6 +2432,8 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
>   	if (!cnt)
>   		return -EINVAL;
>   
> +	if (check_mul_overflow(cnt, (u32)sizeof(*addrs), &size))
> +		return -EOVERFLOW;
>   	size = cnt * sizeof(*addrs);

Same here, 'size = ...' is not needed.

>   	addrs = kvmalloc(size, GFP_KERNEL);
>   	if (!addrs)