linux-kernel - [PATCH] mm: Fix possible off-by-one in walk_pte

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Date:	Tue, 15 Apr 2008 16:00:40 +0200
From:	Johannes Weiner <hannes@...urebad.de>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Johannes Weiner <hannes@...urebad.de>,
	Roel Kluin <12o3l@...cali.nl>, Andreas Schwab <schwab@...e.de>,
	Matt Mackall <mpm@...enic.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] mm: Fix possible off-by-one in walk_pte_range()

After the loop in walk_pte_range() pte might point to the first address
after the pmd it walks.  The pte_unmap() is then applied to something
bad.

Spotted by Roel Kluin and Andreas Schwab.

Signed-off-by: Johannes Weiner <hannes@...urebad.de>
CC: Roel Kluin <12o3l@...cali.nl>
CC: Andreas Schwab <schwab@...e.de>
CC: Matt Mackall <mpm@...enic.com>
CC: Andrew Morton <akpm@...ux-foundation.org>
---

A bug is unlikely, though.  kunmap_atomic() looks up the kmap entry by
map-type instead of the address the pte points.  So the worst thing I
could find with a quick grep was that a wrong TLB entry is being
flushed.  Still, the code is wrong :)

diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index 1cf1417..cf3c004 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -13,7 +13,7 @@ static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 		err = walk->pte_entry(pte, addr, addr + PAGE_SIZE, private);
 		if (err)
 		       break;
-	} while (pte++, addr += PAGE_SIZE, addr != end);
+	} while (addr += PAGE_SIZE, addr != end && pte++);
 
 	pte_unmap(pte);
 	return err;
--
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