Messages in this thread Patch in this message | | | Date | Fri, 21 Aug 2009 16:21:46 -0700 (PDT) | From | David Rientjes <> | Subject | [patch 3/4 -mm] 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.
Cc: Dave Hansen <dave@linux.vnet.ibm.com> Signed-off-by: David Rientjes <rientjes@google.com> --- include/linux/poison.h | 3 +++ lib/flex_array.c | 15 +++++++-------- 2 files changed, 10 insertions(+), 8 deletions(-)
diff --git a/include/linux/poison.h b/include/linux/poison.h --- 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 diff --git a/lib/flex_array.c b/lib/flex_array.c --- a/lib/flex_array.c +++ b/lib/flex_array.c @@ -113,6 +113,8 @@ struct flex_array *flex_array_alloc(int element_size, unsigned int total, return NULL; 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()); return ret; } @@ -159,15 +161,12 @@ __fa_get_part(struct flex_array *fa, int part_nr, gfp_t flags) { struct flex_array_part *part = fa->parts[part_nr]; if (!part) { - /* - * This leaves the part pages uninitialized - * and with potentially random data, just - * as if the user had kmalloc()'d the whole. - * __GFP_ZERO can be used to zero it. - */ - part = kmalloc(FLEX_ARRAY_PART_SIZE, flags); + part = kmalloc(sizeof(struct flex_array_part), flags); if (!part) return NULL; + if (!(flags & __GFP_ZERO)) + memset(part, FLEX_ARRAY_FREE, + sizeof(struct flex_array_part)); fa->parts[part_nr] = part; } return part; @@ -228,7 +227,7 @@ int flex_array_clear(struct flex_array *fa, unsigned int element_nr) return -EINVAL; } dst = &part->elements[index_inside_part(fa, element_nr)]; - memset(dst, 0, fa->element_size); + memset(dst, FLEX_ARRAY_FREE, fa->element_size); return 0; }
| |