linux-kernel - [PATCH] bpftool: fix control flow graph segfault during edge creation

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Message-ID: <20250108220937.1470029-1-christoph.werle@longjmp.de>
Date: Wed,  8 Jan 2025 23:09:37 +0100
From: Christoph Werle <christoph.werle@...gjmp.de>
To: Quentin Monnet <qmo@...nel.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Andrii Nakryiko <andrii@...nel.org>
Cc: Christoph Werle <christoph.werle@...gjmp.de>,
	Daniel Borkmann <daniel@...earbox.net>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] bpftool: fix control flow graph segfault during edge creation

If the last instruction of a control flow graph building block is a
BPF_CALL, an incorrect edge with e->dst set to NULL is created and
results in a segfault during graph output.

Ensure that BPF_CALL as last instruction of a building block is handled
correctly and only generates a single edge unlike actual BPF_JUMP*
instructions.

Signed-off-by: Christoph Werle <christoph.werle@...gjmp.de>
---
 tools/bpf/bpftool/cfg.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/bpf/bpftool/cfg.c b/tools/bpf/bpftool/cfg.c
index eec437cca2ea..e3785f9a697d 100644
--- a/tools/bpf/bpftool/cfg.c
+++ b/tools/bpf/bpftool/cfg.c
@@ -302,6 +302,7 @@ static bool func_add_bb_edges(struct func_node *func)
 
 		insn = bb->tail;
 		if (!is_jmp_insn(insn->code) ||
+		    BPF_OP(insn->code) == BPF_CALL ||
 		    BPF_OP(insn->code) == BPF_EXIT) {
 			e->dst = bb_next(bb);
 			e->flags |= EDGE_FLAG_FALLTHROUGH;
-- 
2.43.0