[PATCH bpf-next v4 4/7] libbpf: Reject gen_loader for objects with already-manual programs
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COLD16d
From: Andrey Grodzovsky <hidden>
Date: 2026-09-21 22:39:58
Subsystem:
bpf [general] (safe dynamic programs and tools), bpf [library] (libbpf), the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Linus Torvalds
Revision v4 of 3 in this series.
Revisions (3)
- v3 [diff vs current]
- v4 current
- v5 [diff vs current]
bpf_program__set_load_strategy()'s MANUAL case rejects setting MANUAL
strategy while a gen_loader is already attached, but a program marked
MANUAL declaratively (SEC("!...")) gets that strategy during
bpf_object__open(), before bpf_object__gen_loader() can ever be
called, so the existing guard can never observe it.
Left unchecked, bpf_object_load_progs() skips such programs, so
gen->nr_progs undercounts relative to the object's real program
count. bpf_gen__finish() only rejects the opposite mismatch direction
(nr_progs < gen->nr_progs), so this passes silently, and every
generated skeleton program slot after the manual one ends up wired to
the wrong prog_fd.
Catch it at the one point guaranteed to run after any MANUAL marking
has already happened: reject in bpf_object__gen_loader() itself if any
program already has load_strategy == BPF_PROG_LOAD_STRATEGY_MANUAL.
Assisted-by: Claude:claude-sonnet-5
Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Andrey Grodzovsky <redacted>
---
tools/lib/bpf/libbpf.c | 34 ++++++++++++++++++++++++----------
1 file changed, 24 insertions(+), 10 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 789d2df7eaae..6e7ec026d944 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c@@ -9788,11 +9788,31 @@ int bpf_object__set_kversion(struct bpf_object *obj, __u32 kern_version) int bpf_object__gen_loader(struct bpf_object *obj, struct gen_loader_opts *opts) { struct bpf_gen *gen; + size_t i; if (!opts) return libbpf_err(-EFAULT); if (!OPTS_VALID(opts, gen_loader_opts)) return libbpf_err(-EINVAL); + + /* + * Manually-loaded programs are not visible to gen_loader (see + * bpf_program__set_load_strategy()'s MANUAL case), and marking a + * program MANUAL happens during bpf_object__open(), before this + * function can ever run, so that guard can never catch it here. + * Reject any pre-existing MANUAL program now, since this is the + * earliest point where both are known. + */ + for (i = 0; i < obj->nr_programs; i++) { + struct bpf_program *prog = &obj->programs[i]; + + if (prog->load_strategy == BPF_PROG_LOAD_STRATEGY_MANUAL) { + pr_warn("prog '%s': gen_loader does not support manually-loaded programs\n", + prog->name); + return libbpf_err(-EOPNOTSUPP); + } + } + gen = calloc(1, sizeof(*gen)); if (!gen) return libbpf_err(-ENOMEM);
@@ -15399,16 +15419,10 @@ int bpf_program__set_load_strategy(struct bpf_program *prog, enum bpf_prog_load_ break; case BPF_PROG_LOAD_STRATEGY_MANUAL: /* - * Manually-loaded programs are not supported for gen_loader. - * This is because bpf_object_load_prog is not called for - * manually-loaded programs, so such programs are not visible - * to gen_loader. For this reason, prevent calling - * bpf_program__set_load_strategy(MANUAL) when gen_loader was - * used to generate a BPF object loader. - * A gen_loader implementation is being called for autoloaded - * programs and defines its own model for loading BPF programs. - * To pass a BPF program to gen_loader, set the program's load strategy - * to BPF_PROG_LOAD_STRATEGY_AUTO. + * Manually-loaded programs are not visible to gen_loader, + * since bpf_object__load_progs() skips them during the bulk + * load pass; see bpf_object__gen_loader()'s own guard for + * the full explanation. */ if (obj->gen_loader) return libbpf_err(-EOPNOTSUPP);
--
2.34.1