flex_arrays: allow zero length flex arrays

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+]

diff --git a/lib/flex_array.c b/lib/flex_array.c
index 0c33b24498ba572f6faaa9b8272264e92779e619..854b57bd7d9d346276fe83599f5cbd306c6e0fe4 100644 (file)
--- 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++) {