Received-SPF: pass (google.com: domain of linux-kernel+bounces-39196-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Precedence: bulk
MIME-Version: 1.0
References: <20240125191840.6740-1-jdamato@fastly.com>
In-Reply-To: <20240125191840.6740-1-jdamato@fastly.com>
From: Eric Dumazet <edumazet@google.com>
Date: Thu, 25 Jan 2024 20:33:56 +0100
Message-ID: <CANn89i+uXsdSVFiQT9fDfGw+h_5QOcuHwPdWi9J=5U6oLXkQTA@mail.gmail.com>
Subject: Re: [PATCH net-next] net: print error if SO_BUSY_POLL_BUDGET is large
To: Joe Damato <jdamato@fastly.com>
Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, dhowells@redhat.com, 
	alexander@mihalicyn.com, leitao@debian.org, wuyun.abel@bytedance.com, 
	kuniyu@amazon.com, pabeni@redhat.com, kuba@kernel.org, davem@davemloft.net
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Thu, Jan 25, 2024 at 8:18=E2=80=AFPM Joe Damato <jdamato@fastly.com> wro=
te:
>
> When drivers call netif_napi_add_weight with a weight that is larger
> than NAPI_POLL_WEIGHT, the networking code allows the larger weight, but
> prints an error.
>
> Replicate this check for SO_BUSY_POLL_BUDGET; check if the user
> specified amount exceeds NAPI_POLL_WEIGHT, allow it anyway, but print an
> error.
>
> Signed-off-by: Joe Damato <jdamato@fastly.com>
> ---
>  net/core/sock.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 158dbdebce6a..ed243bd0dd77 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1153,6 +1153,9 @@ int sk_setsockopt(struct sock *sk, int level, int o=
ptname,
>                         return -EPERM;
>                 if (val < 0 || val > U16_MAX)
>                         return -EINVAL;
> +               if (val > NAPI_POLL_WEIGHT)
> +                       pr_err("SO_BUSY_POLL_BUDGET %u exceeds suggested =
maximum %u\n", val,
> +                              NAPI_POLL_WEIGHT);
>                 WRITE_ONCE(sk->sk_busy_poll_budget, val);
>                 return 0;

This is code run by privileged (CAP_NET_ADMIN) users,
please do not spam the console with such a message.

My point was : Do not allow an unpriv user to set an arbitrary value.

netif_napi_add_weight() is used from kernel drivers, we network
maintainers usually object
if a driver attempts to use a big value, at code review time.