bpf: Enforce that struct_ops programs be GPL-only

With the introduction of the struct_ops program type, it became possible to
implement kernel functionality in BPF, making it viable to use BPF in place
of a regular kernel module for these particular operations.

Thus far, the only user of this mechanism is for implementing TCP
congestion control algorithms. These are clearly marked as GPL-only when
implemented as modules (as seen by the use of EXPORT_SYMBOL_GPL for
tcp_register_congestion_control()), so it seems like an oversight that this
was not carried over to BPF implementations. Since this is the only user
of the struct_ops mechanism, just enforcing GPL-only for the struct_ops
program type seems like the simplest way to fix this.

Fixes: 0baf26b0fcd7 ("bpf: tcp: Support tcp_congestion_ops in bpf")
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20210326100314.121853-1-toke@redhat.com

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 44e4ec1..3a73872 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -12158,6 +12158,11 @@ static int check_struct_ops_btf_id(struct bpf_verifier_env *env)
        u32 btf_id, member_idx;
        const char *mname;
 
+       if (!prog->gpl_compatible) {
+               verbose(env, "struct ops programs must have a GPL compatible license\n");
+               return -EINVAL;
+       }
+
        btf_id = prog->aux->attach_btf_id;
        st_ops = bpf_struct_ops_find(btf_id);
        if (!st_ops) {