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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such that the array parameters are no longer valid.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.

Signed-off-by: David Rientjes <rientjes@google.com>
Acked-by: Dave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
David Rientjes 2009-09-21 17:04:33 -07:00 committed by Linus Torvalds
parent 4af5a2f770
commit 45b588d6e5
2 changed files with 36 additions and 30 deletions
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30
include/linux/flex_array.h
View File

@ -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);

36
lib/flex_array.c
View File

@ -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;