linux-kernel - [PATCH] bitmap: fix bitmap_find_free

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Date:	Fri, 19 Dec 2008 12:26:41 +0100 (CET)
From:	Guennadi Liakhovetski <lg@...x.de>
To:	linux-kernel@...r.kernel.org
cc:	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] bitmap: fix bitmap_find_free_region()

Currently bitmap_find_free_region() assumes, that the requested region 
size is smaller than the entire bitmap. If this is not the case it fails 
to detect it and returns success, while pointing at a position outside of 
the region.

Signed-off-by: Guennadi Liakhovetski <lg@...x.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>
---
It is hard to believe, that this is a bug, last time this code was touched 
in 2006... Or should the caller guarantee, that the requested region is 
not larger than the bitmap? Then dma_alloc_from_coherent() is buggy, which 
is where I hit this bug. But it seems to me bitmap_find_free_region() 
should be fixed.

diff --git a/lib/bitmap.c b/lib/bitmap.c
index 1338469..079c5e3 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -950,6 +950,9 @@ int bitmap_find_free_region(unsigned long *bitmap, int bits, int order)
 {
 	int pos;		/* scans bitmap by regions of size order */
 
+	if (bits < 1 << order)
+		return -ENOMEM;
+
 	for (pos = 0; pos < bits; pos += (1 << order))
 		if (__reg_op(bitmap, pos, order, REG_OP_ISFREE))
 			break;
--
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