Re: [PATCH bpf 1/4] bpf_trace: check size for overflow in bpf_kprobe_multi_link_attach

[Jiri Olsa <olsajiri@gmail.com>]

On Mon, May 16, 2022 at 08:27:08PM +0200, 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@redhat.com>
> ---
>  kernel/trace/bpf_trace.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index d8553f4..e90c4ce7 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2358,6 +2358,8 @@ kprobe_multi_resolve_syms(const void __user *usyms, u32 cnt,
>  	unsigned int i;
>  	char *func;
>  
> +	if (check_mul_overflow(cnt, sizeof(*syms), &size))
> +		return -EOVERFLOW;

there was an update already:

  0236fec57a15 bpf: Resolve symbols with ftrace_lookup_symbols for kprobe multi link

so this won't apply anymore, could you please rebase on top of the latest bpf-next/master?

thanks,
jirka

>  	size = cnt * sizeof(*syms);
>  	syms = kvzalloc(size, GFP_KERNEL);
>  	if (!syms)
> @@ -2429,6 +2431,8 @@ 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);
>  	addrs = kvmalloc(size, GFP_KERNEL);
>  	if (!addrs)
> -- 
> 2.1.4
>