netdev - [PATCH bpf-next 1/4] libbpf: fix detection of BPF helper call instruction

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Date:   Wed, 19 Aug 2020 23:14:08 -0700
From:   Andrii Nakryiko <andriin@...com>
To:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>, <ast@...com>,
        <daniel@...earbox.net>
CC:     <andrii.nakryiko@...il.com>, <kernel-team@...com>,
        Andrii Nakryiko <andriin@...com>, Yonghong Song <yhs@...com>
Subject: [PATCH bpf-next 1/4] libbpf: fix detection of BPF helper call instruction

BPF_CALL | BPF_JMP32 is explicitly not allowed by verifier for BPF helper
calls, so don't detect it as a valid call. Also drop the check on func_id
pointer, as it's currently always non-null.

Reported-by: Yonghong Song <yhs@...com>
Fixes: 109cea5a594f ("libbpf: Sanitize BPF program code for bpf_probe_read_{kernel, user}[_str]")
Signed-off-by: Andrii Nakryiko <andriin@...com>
---
 tools/lib/bpf/libbpf.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 77d420c02094..92ca4eb6ba2d 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -5844,14 +5844,12 @@ static int bpf_object__collect_reloc(struct bpf_object *obj)
 
 static bool insn_is_helper_call(struct bpf_insn *insn, enum bpf_func_id *func_id)
 {
-	__u8 class = BPF_CLASS(insn->code);
-
-	if ((class == BPF_JMP || class == BPF_JMP32) &&
+	if (BPF_CLASS(insn->code) == BPF_JMP &&
 	    BPF_OP(insn->code) == BPF_CALL &&
 	    BPF_SRC(insn->code) == BPF_K &&
-	    insn->src_reg == 0 && insn->dst_reg == 0) {
-		    if (func_id)
-			    *func_id = insn->imm;
+	    insn->src_reg == 0 &&
+	    insn->dst_reg == 0) {
+		    *func_id = insn->imm;
 		    return true;
 	}
 	return false;
-- 
2.24.1