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@xxxxxxxxxxxxx/ Fixes: 0d01da6afc54 ("bpf: implement getsockopt and setsockopt hooks") Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx> Cc: Christian Brauner <brauner@xxxxxxxxxx> Cc: Stanislav Fomichev <sdf@xxxxxxxxxx> Cc: Neil Horman <nhorman@xxxxxxxxxxxxx> Cc: Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx> Cc: Xin Long <lucien.xin@xxxxxxxxx> Cc: linux-sctp@xxxxxxxxxxxxxxx Cc: linux-kernel@xxxxxxxxxxxxxxx Cc: netdev@xxxxxxxxxxxxxxx Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx> --- 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) +{ + /* + * 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
