netdev - [PATCH bpf-next 1/2] bpf: Ensure line_info.insn_off cannot point to insn with zero code

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Date:   Wed, 19 Dec 2018 13:01:01 -0800
From:   Martin KaFai Lau <kafai@...com>
To:     <netdev@...r.kernel.org>
CC:     Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>, <kernel-team@...com>
Subject: [PATCH bpf-next 1/2] bpf: Ensure line_info.insn_off cannot point to insn with zero code

This patch rejects a line_info if the bpf insn code referred by
line_info.insn_off is 0. F.e. a broken userspace tool might generate
a line_info.insn_off that points to the second 8 bytes of a BPF_LD_IMM64.

Signed-off-by: Martin KaFai Lau <kafai@...com>
---
 kernel/bpf/verifier.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 0125731e2512..31c28505811b 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4975,6 +4975,14 @@ static int check_btf_line(struct bpf_verifier_env *env,
 			goto err_free;
 		}
 
+		if (!prog->insnsi[linfo[i].insn_off].code) {
+			verbose(env,
+				"Invalid insn code at line_info[%u].insn_off\n",
+				i);
+			err = -EINVAL;
+			goto err_free;
+		}
+
 		if (!btf_name_by_offset(btf, linfo[i].line_off) ||
 		    !btf_name_by_offset(btf, linfo[i].file_name_off)) {
 			verbose(env, "Invalid line_info[%u].line_off or .file_name_off\n", i);
-- 
2.17.1