flex_array: poison free elements

Newly initialized flex_array's and/or flex_array_part's are now poisoned
with a new poison value, FLEX_ARRAY_FREE.  It's value is similar to
POISON_FREE used in the various slab allocators, but is different to
distinguish between flex array's poisoned kmem and slab allocator poisoned
kmem.

This will allow us to identify flex_array_part's that only contain free
elements (and free them with an addition to the flex_array API).  This
could also be extended in the future to identify `get' uses on elements
that have not been `put'.

If __GFP_ZERO is passed for a part's gfp mask, the poisoning is avoided.
These elements are considered to be in-use since they have been
initialized.

Signed-off-by: David Rientjes <rientjes@google.com>
Cc: 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>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/poison.h b/include/linux/poison.h
index 6729f7dcd60e..7fc194aef8c2 100644
--- a/include/linux/poison.h
+++ b/include/linux/poison.h
@@ -65,6 +65,9 @@
 #define MUTEX_DEBUG_INIT        0x11
 #define MUTEX_DEBUG_FREE        0x22
 
+/********** lib/flex_array.c **********/
+#define FLEX_ARRAY_FREE 0x6c    /* for use-after-free poisoning */
+
 /********** security/ **********/
 #define KEY_DESTROY             0xbd