Subject: Re: [PATCH bpf-next v2 01/28] bpf: add new is_sys_admin_prog_type() helper

From: Sean Young <[email-masked]>
Date: Wed, 9 Mar 2022 08:27:11 +0000

On Fri, Mar 04, 2022 at 06:28:25PM +0100, Benjamin Tissoires wrote:
> LIRC_MODE2 does not really need net_admin capability, but only sys_admin.
> 
> Extract a new helper for it, it will be also used for the HID bpf
> implementation.
> 
> Cc: Sean Young <[email-masked]>
> Signed-off-by: Benjamin Tissoires <[email-masked]>

For BPF_PROG_TYPE_LIRC_MODE2, I don't think this change will break userspace.
This is called from ir-keytable(1) which is called from udev. It should have
all the necessary permissions.

In addition, the vast majority IR decoders are non-bpf. bpf ir decoders have
very few users at the moment.

Acked-by: Sean Young <[email-masked]>

Sean

> 
> ---
> 
> new in v2
> ---
>  kernel/bpf/syscall.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index db402ebc5570..cc570891322b 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -2165,7 +2165,6 @@ static bool is_net_admin_prog_type(enum bpf_prog_type prog_type)
>  	case BPF_PROG_TYPE_LWT_SEG6LOCAL:
>  	case BPF_PROG_TYPE_SK_SKB:
>  	case BPF_PROG_TYPE_SK_MSG:
> -	case BPF_PROG_TYPE_LIRC_MODE2:
>  	case BPF_PROG_TYPE_FLOW_DISSECTOR:
>  	case BPF_PROG_TYPE_CGROUP_DEVICE:
>  	case BPF_PROG_TYPE_CGROUP_SOCK:
> @@ -2202,6 +2201,17 @@ static bool is_perfmon_prog_type(enum bpf_prog_type prog_type)
>  	}
>  }
>  
> +static bool is_sys_admin_prog_type(enum bpf_prog_type prog_type)
> +{
> +	switch (prog_type) {
> +	case BPF_PROG_TYPE_LIRC_MODE2:
> +	case BPF_PROG_TYPE_EXT: /* extends any prog */
> +		return true;
> +	default:
> +		return false;
> +	}
> +}
> +
>  /* last field in 'union bpf_attr' used by this command */
>  #define	BPF_PROG_LOAD_LAST_FIELD core_relo_rec_size
>  
> @@ -2252,6 +2262,8 @@ static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr)
>  		return -EPERM;
>  	if (is_perfmon_prog_type(type) && !perfmon_capable())
>  		return -EPERM;
> +	if (is_sys_admin_prog_type(type) && !capable(CAP_SYS_ADMIN))
> +		return -EPERM;
>  
>  	/* attach_prog_fd/attach_btf_obj_fd can specify fd of either bpf_prog
>  	 * or btf, we need to check which one it is
> -- 
> 2.35.1