linux-kernel - [PATCH 3.16.y-ckt 096/110] lguest: fix out-by-one error in address checking.

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Message-Id: <1433512713-22984-97-git-send-email-luis.henriques@canonical.com>
Date:	Fri,  5 Jun 2015 14:58:19 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 096/110] lguest: fix out-by-one error in address checking.

3.16.7-ckt13 -stable review patch.  If anyone has any objections, please let me know.

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

From: Rusty Russell <rusty@...tcorp.com.au>

commit 83a35114d0e4583e6b0ca39502e68b6a92e2910c upstream.

This bug has been there since day 1; addresses in the top guest physical
page weren't considered valid.  You could map that page (the check in
check_gpte() is correct), but if a guest tried to put a pagetable there
we'd check that address manually when walking it, and kill the guest.

Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 drivers/lguest/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c
index 0bf1e4edf04d..19da22249bd8 100644
--- a/drivers/lguest/core.c
+++ b/drivers/lguest/core.c
@@ -176,7 +176,7 @@ static void unmap_switcher(void)
 bool lguest_address_ok(const struct lguest *lg,
 		       unsigned long addr, unsigned long len)
 {
-	return (addr+len) / PAGE_SIZE < lg->pfn_limit && (addr+len >= addr);
+	return addr+len <= lg->pfn_limit * PAGE_SIZE && (addr+len >= addr);
 }
 
 /*
--
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