linux-kernel - [PATCH 4.2.y-ckt 211/273] x86/mpx: Fix off-by-one comparison with nr

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Message-Id: <1457391064-6660-212-git-send-email-kamal@canonical.com>
Date:	Mon,  7 Mar 2016 14:50:02 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Colin Ian King <colin.king@...onical.com>,
	Borislav Petkov <bp@...en8.de>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 211/273] x86/mpx: Fix off-by-one comparison with nr_registers

4.2.8-ckt5 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Colin Ian King <colin.king@...onical.com>

commit 9bf148cb0812595bfdf5100bd2c07e9bec9c6ef5 upstream.

In the unlikely event that regno == nr_registers then we get an array
overrun on regoff because the invalid register check is currently
off-by-one. Fix this with a check that regno is >= nr_registers instead.

Detected with static analysis using CoverityScan.

Fixes: fcc7ffd67991 "x86, mpx: Decode MPX instruction to get bound violation information"
Signed-off-by: Colin Ian King <colin.king@...onical.com>
Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Link: http://lkml.kernel.org/r/1456512931-3388-1-git-send-email-colin.king@canonical.com
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 arch/x86/mm/mpx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
index 27f8393..b77009c 100644
--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -160,7 +160,7 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
 		break;
 	}
 
-	if (regno > nr_registers) {
+	if (regno >= nr_registers) {
 		WARN_ONCE(1, "decoded an instruction with an invalid register");
 		return -EINVAL;
 	}
-- 
2.7.0