netdev - [PATCH] ebpf: emit correct src

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Message-Id: <1441931107-17673-1-git-send-email-tycho.andersen@canonical.com>
Date:	Thu, 10 Sep 2015 18:25:07 -0600
From:	Tycho Andersen <tycho.andersen@...onical.com>
To:	Alexei Starovoitov <ast@...nel.org>,
	"David S. Miller" <davem@...emloft.net>
Cc:	netdev@...r.kernel.org,
	Tycho Andersen <tycho.andersen@...onical.com>,
	Daniel Borkmann <daniel@...earbox.net>
Subject: [PATCH] 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@...onical.com>
CC: Alexei Starovoitov <ast@...nel.org>
CC: Daniel Borkmann <daniel@...earbox.net>
---
 net/core/filter.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 13079f0..05a04ea 100644
--- 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. */
-- 
2.1.4

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