ebpf: emit correct src_reg for conditional jumps

Instead of always emitting BPF_REG_X, let's emit BPF_REG_X only when the
source actually is BPF_X. This causes programs generated by the classic
converter to not be importable via bpf(), as the eBPF verifier checks that
the src_reg is correct or 0. While not a problem yet, this will be a
problem when BPF_PROG_DUMP lands, and we can potentially dump and re-import
programs generated by the converter.

Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
CC: Alexei Starovoitov <ast@kernel.org>
CC: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/filter.c b/net/core/filter.c
index 13079f03902e7674b7cd71bf01ca1d12844c758b..05a04ea871728d2c18f68571321e9435df1f3b18 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -478,9 +478,9 @@ do_pass:
                                bpf_src = BPF_X;
                        } else {
                                insn->dst_reg = BPF_REG_A;
-                               insn->src_reg = BPF_REG_X;
                                insn->imm = fp->k;
                                bpf_src = BPF_SRC(fp->code);
+                               insn->src_reg = bpf_src == BPF_X ? BPF_REG_X : 0;
                        }
 
                        /* Common case where 'jump_false' is next insn. */