linux-kernel - [51/67] net: bpf_jit: fix an off-one bug in x86

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Message-Id: <20120103223035.624344514@clark.kroah.org>
Date:	Tue, 03 Jan 2012 14:30:09 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk,
	Markus Kötter <nepenthesdev@...il.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [51/67] net: bpf_jit: fix an off-one bug in x86_64 cond jump target

3.0-stable review patch.  If anyone has any objections, please let me know.

------------------


From: Markus Kötter <nepenthesdev@...il.com>

[ Upstream commit a03ffcf873fe0f2565386ca8ef832144c42e67fa ]

x86 jump instruction size is 2 or 5 bytes (near/long jump), not 2 or 6
bytes.

In case a conditional jump is followed by a long jump, conditional jump
target is one byte past the start of target instruction.

Signed-off-by: Markus Kötter <nepenthesdev@...il.com>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
---
 arch/x86/net/bpf_jit_comp.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -568,8 +568,8 @@ cond_branch:			f_offset = addrs[i + filt
 					break;
 				}
 				if (filter[i].jt != 0) {
-					if (filter[i].jf)
-						t_offset += is_near(f_offset) ? 2 : 6;
+					if (filter[i].jf && f_offset)
+						t_offset += is_near(f_offset) ? 2 : 5;
 					EMIT_COND_JMP(t_op, t_offset);
 					if (filter[i].jf)
 						EMIT_JMP(f_offset);


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