While working on the ebpf-go [0] library integration for bpf_mprog and tcx, Lorenz noticed that two subsequent BPF_PROG_QUERY requests currently fail. A typical workflow is to first gather the bpf_mprog count without passing program/ link arrays, followed by the second request which contains the actual array pointers. The initial call populates count and revision fields. The second call gets rejected due to a BPF_PROG_QUERY_LAST_FIELD bug which should point to query.revision instead of query.link_attach_flags since the former is really the last member. It was not noticed in libbpf as bpf_prog_query_opts() always calls bpf(2) with an on-stack bpf_attr that is memset() each time (and therefore query.revision was reset to zero). [0] https://ebpf-go.dev Fixes: e420bed02507 ("bpf: Add fd-based tcx multi-prog infra with link support") Reported-by: Lorenz Bauer <lmb@xxxxxxxxxxxxx> Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx> --- kernel/bpf/syscall.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index eb01c31ed591..453a43695a23 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -3913,7 +3913,7 @@ static int bpf_prog_detach(const union bpf_attr *attr) return ret; } -#define BPF_PROG_QUERY_LAST_FIELD query.link_attach_flags +#define BPF_PROG_QUERY_LAST_FIELD query.revision static int bpf_prog_query(const union bpf_attr *attr, union bpf_attr __user *uattr) -- 2.34.1
