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

Sean Young
2022-03-09T08:27:20Z

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 <sean@mess.org>
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

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 <sean@mess.org>

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