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@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e0e77ff..5c64281 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4980,6 +4980,14 @@ 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);