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SubjectRe: [PATCH net-next] sctp: add bpf_bypass_getsockopt proto callback
On Wed, May 10, 2023 at 6:15 AM Alexander Mikhalitsyn
<aleksandr.mikhalitsyn@canonical.com> wrote:
>
> Add bpf_bypass_getsockopt proto callback and filter out
> SCTP_SOCKOPT_PEELOFF and SCTP_SOCKOPT_PEELOFF_FLAGS socket options
> from running eBPF hook on them.
>
> These options do fd_install(), and if BPF_CGROUP_RUN_PROG_GETSOCKOPT
> hook returns an error after success of the original handler
> sctp_getsockopt(...), userspace will receive an error from getsockopt
> syscall and will be not aware that fd was successfully installed into fdtable.
>
> This patch was born as a result of discussion around a new SCM_PIDFD interface:
> https://lore.kernel.org/all/20230413133355.350571-3-aleksandr.mikhalitsyn@canonical.com/
>
> Fixes: 0d01da6afc54 ("bpf: implement getsockopt and setsockopt hooks")
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: Christian Brauner <brauner@kernel.org>
> Cc: Stanislav Fomichev <sdf@google.com>
> Cc: Neil Horman <nhorman@tuxdriver.com>
> Cc: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
> Cc: Xin Long <lucien.xin@gmail.com>
> Cc: linux-sctp@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: netdev@vger.kernel.org
> Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>

Acked-by: Stanislav Fomichev <sdf@google.com>

with a small nit below

> ---
> net/sctp/socket.c | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
>
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index cda8c2874691..a9a0ababea90 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -8281,6 +8281,29 @@ static int sctp_getsockopt(struct sock *sk, int level, int optname,
> return retval;
> }
>

[...]

> +bool sctp_bpf_bypass_getsockopt(int level, int optname)

static bool ... ? You're not making it indirect-callable, so seems
fine to keep private to this compilation unit?

> +{
> + /*
> + * These options do fd_install(), and if BPF_CGROUP_RUN_PROG_GETSOCKOPT
> + * hook returns an error after success of the original handler
> + * sctp_getsockopt(...), userspace will receive an error from getsockopt
> + * syscall and will be not aware that fd was successfully installed into fdtable.
> + *
> + * Let's prevent bpf cgroup hook from running on them.
> + */
> + if (level == SOL_SCTP) {
> + switch (optname) {
> + case SCTP_SOCKOPT_PEELOFF:
> + case SCTP_SOCKOPT_PEELOFF_FLAGS:
> + return true;
> + default:
> + return false;
> + }
> + }
> +
> + return false;
> +}
> +
> static int sctp_hash(struct sock *sk)
> {
> /* STUB */
> @@ -9650,6 +9673,7 @@ struct proto sctp_prot = {
> .shutdown = sctp_shutdown,
> .setsockopt = sctp_setsockopt,
> .getsockopt = sctp_getsockopt,
> + .bpf_bypass_getsockopt = sctp_bpf_bypass_getsockopt,
> .sendmsg = sctp_sendmsg,
> .recvmsg = sctp_recvmsg,
> .bind = sctp_bind,
> @@ -9705,6 +9729,7 @@ struct proto sctpv6_prot = {
> .shutdown = sctp_shutdown,
> .setsockopt = sctp_setsockopt,
> .getsockopt = sctp_getsockopt,
> + .bpf_bypass_getsockopt = sctp_bpf_bypass_getsockopt,
> .sendmsg = sctp_sendmsg,
> .recvmsg = sctp_recvmsg,
> .bind = sctp_bind,
> --
> 2.34.1
>

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