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Subject[PATCH net-next v2] sctp: add bpf_bypass_getsockopt proto callback
Date
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
Suggested-by: Stanislav Fomichev <sdf@google.com>
Acked-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
---
net/sctp/socket.c | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index cda8c2874691..fed6057beb60 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;
}

+static bool sctp_bpf_bypass_getsockopt(int level, int optname)
+{
+ /*
+ * 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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