linux-kernel - [patch 1/3] flex_array: fix get function for elements in base starting at non-zero

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Date:	Mon, 17 Aug 2009 16:46:18 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Dave Hansen <dave@...ux.vnet.ibm.com>, linux-kernel@...r.kernel.org
Subject: [patch 1/3] flex_array: fix get function for elements in base starting
 at non-zero

If all array elements fit into the base structure and data is copied
using flex_array_put() starting at a non-zero index, flex_array_get()
will fail to return the data.

This fixes the bug by only checking for NULL parts when all elements do
not fit in the base structure when flex_array_get() is used.  Otherwise,
fa_element_to_part_nr() will always be 0 since there are no parts
structures needed and such element may never have been put.  Thus, it
will remain NULL due to the kzalloc() of the base.

Additionally, flex_array_put() now only checks for a NULL part when all
elements do not fit in the base structure.  This is otherwise unnecessary
since the base structure is guaranteed to exist (or we would have already
hit a NULL pointer).

Cc: Dave Hansen <dave@...ux.vnet.ibm.com>
Signed-off-by: David Rientjes <rientjes@...gle.com>
---
 lib/flex_array.c |   14 ++++++++------
 1 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/lib/flex_array.c b/lib/flex_array.c
--- a/lib/flex_array.c
+++ b/lib/flex_array.c
@@ -198,10 +198,11 @@ int flex_array_put(struct flex_array *fa, int element_nr, void *src, gfp_t flags
 		return -ENOSPC;
 	if (elements_fit_in_base(fa))
 		part = (struct flex_array_part *)&fa->parts[0];
-	else
+	else {
 		part = __fa_get_part(fa, part_nr, flags);
-	if (!part)
-		return -ENOMEM;
+		if (!part)
+			return -ENOMEM;
+	}
 	dst = &part->elements[index_inside_part(fa, element_nr)];
 	memcpy(dst, src, fa->element_size);
 	return 0;
@@ -257,11 +258,12 @@ void *flex_array_get(struct flex_array *fa, int element_nr)

 	if (element_nr >= fa->total_nr_elements)
 		return NULL;
-	if (!fa->parts[part_nr])
-		return NULL;
 	if (elements_fit_in_base(fa))
 		part = (struct flex_array_part *)&fa->parts[0];
-	else
+	else {
 		part = fa->parts[part_nr];
+		if (!part)
+			return NULL;
+	}
 	return &part->elements[index_inside_part(fa, element_nr)];
 }
--
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