linux-kernel - [PATCH] fix broken size test in bitmap_find_free

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Date:	Fri, 6 Feb 2009 13:22:33 +0100 (CET)
From:	Guennadi Liakhovetski <lg@...x.de>
To:	linux-kernel@...r.kernel.org
cc:	Paul Mundt <lethal@...ux-sh.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	adrian@...golddream.dyndns.info, lkmladrian@...il.com,
	linux-sh@...r.kernel.org, penberg@...helsinki.fi,
	dbaryshkov@...il.com, penguin-kernel@...ove.sakura.ne.jp,
	hannes@...xchg.org
Subject: [PATCH] fix broken size test in bitmap_find_free_region()

This loop and test in bitmap_find_free_region()

	for (pos = 0; pos < bits; pos += (1 << order))
		if (__reg_op(bitmap, pos, order, REG_OP_ISFREE))
			break;
	if (pos == bits)
		return -ENOMEM;

can only return an error (-ENOMEM) if bits is a multiple of (1 << order), 
which is, for instance, true, if bits is (also) a power of 2. This 
is not necessarily the case with dma_alloc_from_coherent(). A failure to 
recognise too large a request leads in dma_alloc_from_coherent() to 
accessing beyond available memory, and to writing beyond the bitmap.

Signed-off-by: Guennadi Liakhovetski <lg@...x.de>
---

diff --git a/lib/bitmap.c b/lib/bitmap.c
index 1338469..d49c37f 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -953,7 +953,7 @@ int bitmap_find_free_region(unsigned long *bitmap, int bits, int order)
 	for (pos = 0; pos < bits; pos += (1 << order))
 		if (__reg_op(bitmap, pos, order, REG_OP_ISFREE))
 			break;
-	if (pos == bits)
+	if (pos + (1 << order) > bits)
 		return -ENOMEM;
 	__reg_op(bitmap, pos, order, REG_OP_ALLOC);
 	return pos;
--
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