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

[Jiri Olsa]

On Tue, May 17, 2022 at 09:36:15AM +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.  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@xxxxxxxxxxxxxxx> # 5.18
> Signed-off-by: Eugene Syromiatnikov <esyr@xxxxxxxxxx>

Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>

thanks,
jirka

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