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bpf-firewall: attach with BPF_F_ALLOW_MULTI if kernel supports

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Reduced version of [0].
Use BPF_F_ALLOW_MULTI attach flag for bpf-firewall if kernel supports
it.

Aside from addressing security issue in [0] attaching with 'multi'
allows further attaching of cgroup egress, ingress hooks specified by
BPFProgram=.

[0] 4e42210d40
This commit is contained in:
Julia Kartseva 2021-02-03 22:15:27 -08:00
parent e2e40e9a9e
commit a442ccb4eb
1 changed files with 3 additions and 6 deletions
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9
src/core/bpf-firewall.c
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@ -698,8 +698,7 @@ int bpf_firewall_install(Unit *u) {
if (r < 0)
return log_unit_error_errno(u, r, "Failed to determine cgroup path: %m");
flags = (supported == BPF_FIREWALL_SUPPORTED_WITH_MULTI &&
(u->type == UNIT_SLICE || unit_cgroup_delegate(u))) ? BPF_F_ALLOW_MULTI : 0;
flags = supported == BPF_FIREWALL_SUPPORTED_WITH_MULTI ? BPF_F_ALLOW_MULTI : 0;
/* Unref the old BPF program (which will implicitly detach it) right before attaching the new program, to
* minimize the time window when we don't account for IP traffic. */
@ -707,8 +706,7 @@ int bpf_firewall_install(Unit *u) {
u->ip_bpf_ingress_installed = bpf_program_unref(u->ip_bpf_ingress_installed);
if (u->ip_bpf_egress) {
r = bpf_program_cgroup_attach(u->ip_bpf_egress, BPF_CGROUP_INET_EGRESS, path,
flags | (set_isempty(u->ip_bpf_custom_egress) ? 0 : BPF_F_ALLOW_MULTI));
r = bpf_program_cgroup_attach(u->ip_bpf_egress, BPF_CGROUP_INET_EGRESS, path, flags);
if (r < 0)
return log_unit_error_errno(u, r, "Attaching egress BPF program to cgroup %s failed: %m", path);
@ -717,8 +715,7 @@ int bpf_firewall_install(Unit *u) {
}
if (u->ip_bpf_ingress) {
r = bpf_program_cgroup_attach(u->ip_bpf_ingress, BPF_CGROUP_INET_INGRESS, path,
flags | (set_isempty(u->ip_bpf_custom_ingress) ? 0 : BPF_F_ALLOW_MULTI));
r = bpf_program_cgroup_attach(u->ip_bpf_ingress, BPF_CGROUP_INET_INGRESS, path, flags);
if (r < 0)
return log_unit_error_errno(u, r, "Attaching ingress BPF program to cgroup %s failed: %m", path);