[PATCH -v2] flex_arrays: allow zero length flex arrays

[PATCH -v2] flex_arrays: allow zero length flex arrays

[Eric Paris]

Just like kmalloc will allow one to allocate a 0 length segment of memory
flex arrays should do the same thing.  It should bomb if you try to use
something, but it should at least allow the allocation.

This is needed because when SELinux switched to using flex_arrays in 2.6.38
the inability to allocate a 0 length array resulted in SELinux policy load
returning -ENOSPC when previously it worked.

Based-on-patch-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Eric Paris <eparis@redhat.com>
Tested-by: Chris Richards <gizmo@giz-works.com>
Cc: stable@kernel.org [2.6.38+]
---

 lib/flex_array.c |   11 ++++++++++-
 1 files changed, 10 insertions(+), 1 deletions(-)

diff --git a/lib/flex_array.c b/lib/flex_array.c
index 0c33b24..854b57b 100644
--- a/lib/flex_array.c
+++ b/lib/flex_array.c
@@ -253,9 +253,16 @@ int flex_array_prealloc(struct flex_array *fa, unsigned int start,
 	unsigned int end;
 	struct flex_array_part *part;
 
+	if (!start && !nr_elements)
+		return 0;
+	if (start >= fa->total_nr_elements)
+		return -ENOSPC;
+	if (!nr_elements)
+		return 0;
+
 	end = start + nr_elements - 1;
 
-	if (start >= fa->total_nr_elements || end >= fa->total_nr_elements)
+	if (end >= fa->total_nr_elements)
 		return -ENOSPC;
 	if (elements_fit_in_base(fa))
 		return 0;
@@ -346,6 +353,8 @@ int flex_array_shrink(struct flex_array *fa)
 	int part_nr;
 	int ret = 0;
 
+	if (!fa->total_nr_elements)
+		return 0;
 	if (elements_fit_in_base(fa))
 		return ret;
 	for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) {

Re: [PATCH -v2] flex_arrays: allow zero length flex arrays

[James Morris]

On Thu, 28 Apr 2011, Eric Paris wrote:

> Just like kmalloc will allow one to allocate a 0 length segment of memory
> flex arrays should do the same thing.  It should bomb if you try to use
> something, but it should at least allow the allocation.

This patch does not apply to current -linus.

-- 
James Morris
<jmorris@namei.org>

Re: [PATCH -v2] flex_arrays: allow zero length flex arrays

[Eric Paris]

It builds on another patch already committed to my tree.  I'll send
you a pull request for that branch right now!

-Eric

On Mon, May 2, 2011 at 8:20 PM, James Morris <jmorris@namei.org> wrote:
> On Thu, 28 Apr 2011, Eric Paris wrote:
>
>> Just like kmalloc will allow one to allocate a 0 length segment of memory
>> flex arrays should do the same thing.  It should bomb if you try to use
>> something, but it should at least allow the allocation.
>
> This patch does not apply to current -linus.
>
> --
> James Morris
> <jmorris@namei.org>
> --
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