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Date: Tue, 1 Sep 2009 20:14:30 -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 1/2 -mm] flex_array: introduce DEFINE_FLEX_ARRAY
FLEX_ARRAY_INIT(element_size, total_nr_elements) cannot determine if
either parameter is valid, so flex arrays which are statically allocated
with this interface can easily become corrupted or reference beyond its
allocated memory.
This removes FLEX_ARRAY_INIT() as a struct flex_array initializer since
no initializer may perform the required checking. Instead, the array
is now defined with a new interface:
DEFINE_FLEX_ARRAY(name, element_size, total_nr_elements)
This may be prefixed with `static' for file scope.
This interface includes compile-time checking of the parameters to
ensure they are valid. Since the validity of both element_size and
total_nr_elements depend on FLEX_ARRAY_BASE_SIZE and
FLEX_ARRAY_PART_SIZE, the kernel build will fail if either of these
predefined values changes such that the array parameters are no longer
valid.
Since BUILD_BUG_ON() requires compile time constants, several of the
static inline functions that were once local to lib/flex_array.c had to
be moved to include/linux/flex_array.h.
Cc: Dave Hansen <dave@...ux.vnet.ibm.com>
Signed-off-by: David Rientjes <rientjes@...gle.com>
---
include/linux/flex_array.h | 30 ++++++++++++++++++++++++++----
lib/flex_array.c | 36 ++++++++++--------------------------
2 files changed, 36 insertions(+), 30 deletions(-)
diff --git a/include/linux/flex_array.h b/include/linux/flex_array.h
--- a/include/linux/flex_array.h
+++ b/include/linux/flex_array.h
@@ -31,10 +31,32 @@ struct flex_array {
};
};
-#define FLEX_ARRAY_INIT(size, total) { { {\
- .element_size = (size), \
- .total_nr_elements = (total), \
-} } }
+/* Number of bytes left in base struct flex_array, excluding metadata */
+#define FLEX_ARRAY_BASE_BYTES_LEFT \
+ (FLEX_ARRAY_BASE_SIZE - offsetof(struct flex_array, parts))
+
+/* Number of pointers in base to struct flex_array_part pages */
+#define FLEX_ARRAY_NR_BASE_PTRS \
+ (FLEX_ARRAY_BASE_BYTES_LEFT / sizeof(struct flex_array_part *))
+
+/* Number of elements of size that fit in struct flex_array_part */
+#define FLEX_ARRAY_ELEMENTS_PER_PART(size) \
+ (FLEX_ARRAY_PART_SIZE / size)
+
+/*
+ * Defines a statically allocated flex array and ensures its parameters are
+ * valid.
+ */
+#define DEFINE_FLEX_ARRAY(__arrayname, __element_size, __total) \
+ struct flex_array __arrayname = { { { \
+ .element_size = (__element_size), \
+ .total_nr_elements = (__total), \
+ } } }; \
+ static inline void __arrayname##_invalid_parameter(void) \
+ { \
+ BUILD_BUG_ON((__total) > FLEX_ARRAY_NR_BASE_PTRS * \
+ FLEX_ARRAY_ELEMENTS_PER_PART(__element_size)); \
+ }
struct flex_array *flex_array_alloc(int element_size, unsigned int total,
gfp_t flags);
diff --git a/lib/flex_array.c b/lib/flex_array.c
--- a/lib/flex_array.c
+++ b/lib/flex_array.c
@@ -28,23 +28,6 @@ struct flex_array_part {
char elements[FLEX_ARRAY_PART_SIZE];
};
-static inline int __elements_per_part(int element_size)
-{
- return FLEX_ARRAY_PART_SIZE / element_size;
-}
-
-static inline int bytes_left_in_base(void)
-{
- int element_offset = offsetof(struct flex_array, parts);
- int bytes_left = FLEX_ARRAY_BASE_SIZE - element_offset;
- return bytes_left;
-}
-
-static inline int nr_base_part_ptrs(void)
-{
- return bytes_left_in_base() / sizeof(struct flex_array_part *);
-}
-
/*
* If a user requests an allocation which is small
* enough, we may simply use the space in the
@@ -54,7 +37,7 @@ static inline int nr_base_part_ptrs(void)
static inline int elements_fit_in_base(struct flex_array *fa)
{
int data_size = fa->element_size * fa->total_nr_elements;
- if (data_size <= bytes_left_in_base())
+ if (data_size <= FLEX_ARRAY_BASE_BYTES_LEFT)
return 1;
return 0;
}
@@ -103,7 +86,8 @@ struct flex_array *flex_array_alloc(int element_size, unsigned int total,
gfp_t flags)
{
struct flex_array *ret;
- int max_size = nr_base_part_ptrs() * __elements_per_part(element_size);
+ int max_size = FLEX_ARRAY_NR_BASE_PTRS *
+ FLEX_ARRAY_ELEMENTS_PER_PART(element_size);
/* max_size will end up 0 if element_size > PAGE_SIZE */
if (total > max_size)
@@ -114,14 +98,15 @@ struct flex_array *flex_array_alloc(int element_size, unsigned int total,
ret->element_size = element_size;
ret->total_nr_elements = total;
if (elements_fit_in_base(ret) && !(flags & __GFP_ZERO))
- memset(ret->parts[0], FLEX_ARRAY_FREE, bytes_left_in_base());
+ memset(ret->parts[0], FLEX_ARRAY_FREE,
+ FLEX_ARRAY_BASE_BYTES_LEFT);
return ret;
}
static int fa_element_to_part_nr(struct flex_array *fa,
unsigned int element_nr)
{
- return element_nr / __elements_per_part(fa->element_size);
+ return element_nr / FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size);
}
/**
@@ -133,11 +118,10 @@ static int fa_element_to_part_nr(struct flex_array *fa,
void flex_array_free_parts(struct flex_array *fa)
{
int part_nr;
- int max_part = nr_base_part_ptrs();
if (elements_fit_in_base(fa))
return;
- for (part_nr = 0; part_nr < max_part; part_nr++)
+ for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++)
kfree(fa->parts[part_nr]);
}
@@ -152,7 +136,8 @@ static unsigned int index_inside_part(struct flex_array *fa,
{
unsigned int part_offset;
- part_offset = element_nr % __elements_per_part(fa->element_size);
+ part_offset = element_nr %
+ FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size);
return part_offset * fa->element_size;
}
@@ -313,13 +298,12 @@ static int part_is_free(struct flex_array_part *part)
int flex_array_shrink(struct flex_array *fa)
{
struct flex_array_part *part;
- int max_part = nr_base_part_ptrs();
int part_nr;
int ret = 0;
if (elements_fit_in_base(fa))
return ret;
- for (part_nr = 0; part_nr < max_part; part_nr++) {
+ for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) {
part = fa->parts[part_nr];
if (!part)
continue;
--
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