Messages in this thread Patch in this message | | | Date | Tue, 14 Feb 2012 15:24:58 -0600 (CST) | From | Christoph Lameter <> | Subject | Re: Uninline kcalloc |
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On Tue, 14 Feb 2012, Nick Bowler wrote:
> On 2012-02-14 13:37 -0600, Christoph Lameter wrote: > > This patch still preserves kcalloc. But note that if kcalloc returns NULL > > then multiple conditions may have caused it. One is that the array is > > simply too large. The other may be that such an allocation is not possible > > due to fragmentation. > [...] > > +static inline long calculate_array_size(size_t n, size_t size) > > +{ > > + if (size != 0 && n > ULONG_MAX / size) > > + > > + return 0; > > This isn't right. The above tests whether or not the result of the > multiplication will not be representable in an 'unsigned long'...
Yes and so does the current kcalloc.
> > + return n * size; > > but then the result is assigned to a (signed) long, which may overflow > if it's greater than LONG_MAX.
That can happen? But you are right its better to use the size_t as the result of the argument. There is a gooh of long / size_t confusion already. This useless function should not be in the kernel.
> > +} > [...] > > void *kcalloc(size_t n, size_t size, gfp_t flags) > > { > > - if (size != 0 && n > ULONG_MAX / size) > > - return NULL; > > - return __kmalloc(n * size, flags | __GFP_ZERO); > > + size_t s = calculate_array_size(n, size); > > + > > + if (s) > > + return kzalloc(s, flags); > > + > > + return NULL; > > } > > This hunk changes the behaviour of kcalloc if either of the two size parameters > is 0.
You want ZERO_PTR returns?
NULL is one permissible return value of calloc() if size == 0. So we are now deviating from user space conventions.
Subject: Introduce calculate_array_size
calculate_array_size calculates the size of an array while checking for errors. Returns 0 if the size is too large.
Signed-off-by: Christoph Lameter <cl@linux.com>
--- include/linux/slab.h | 15 +++++++++++++++ mm/util.c | 7 +++++-- 2 files changed, 20 insertions(+), 2 deletions(-)
Index: linux-2.6/include/linux/slab.h =================================================================== --- linux-2.6.orig/include/linux/slab.h 2012-02-14 15:16:53.000000000 -0600 +++ linux-2.6/include/linux/slab.h 2012-02-14 15:21:39.000000000 -0600 @@ -242,6 +242,21 @@ size_t ksize(const void *); */ void *kcalloc(size_t n, size_t size, gfp_t flags);
+/* + * calculate_array_size - Calculate an array size given the size of a + * particular element with checking for overflow. + * + * Return 0 if there is an overflow. + */ +static inline size_t calculate_array_size(size_t n, size_t size) +{ + if (n > ULONG_MAX / size) + + return 0; + + return n * size; +} + #if !defined(CONFIG_NUMA) && !defined(CONFIG_SLOB) /** * kmalloc_node - allocate memory from a specific node Index: linux-2.6/mm/util.c =================================================================== --- linux-2.6.orig/mm/util.c 2012-02-14 15:16:53.000000000 -0600 +++ linux-2.6/mm/util.c 2012-02-14 15:21:05.000000000 -0600 @@ -83,9 +83,12 @@ EXPORT_SYMBOL(kmemdup); */ void *kcalloc(size_t n, size_t size, gfp_t flags) { - if (size != 0 && n > ULONG_MAX / size) + size_t s = calculate_array_size(n, size); + + if (size && !s) return NULL; - return __kmalloc(n * size, flags | __GFP_ZERO); + + return kzalloc(s, flags); } EXPORT_SYMBOL(kcalloc);
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