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.

v3: No change
v2: Move check to the top of check_struct_ops_btf_id().

Fixes: 0baf26b0fcd7 ("bpf: tcp: Support tcp_congestion_ops in bpf")
Acked-by: Martin KaFai Lau <ka...@fb.com>
Signed-off-by: Toke Høiland-Jørgensen <t...@redhat.com>
---
 kernel/bpf/verifier.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 44e4ec1640f1..3a738724a380 100644
--- 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) {
-- 
2.31.0

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