On 07/25/2016 01:45 PM, Kees Cook wrote:

On Mon, Jul 25, 2016 at 12:16 PM, Laura Abbott [off-list ref] wrote:

quoted

On 07/20/2016 01:27 PM, Kees Cook wrote:

quoted

Under CONFIG_HARDENED_USERCOPY, this adds object size checking to the
SLUB allocator to catch any copies that may span objects. Includes a
redzone handling fix discovered by Michael Ellerman.

Based on code from PaX and grsecurity.

Signed-off-by: Kees Cook <redacted>
Tested-by: Michael Ellerman <mpe@ellerman.id.au>
---
 init/Kconfig |  1 +
 mm/slub.c    | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/init/Kconfig b/init/Kconfig
index 798c2020ee7c..1c4711819dfd 100644
--- a/init/Kconfig
+++ b/init/Kconfig

@@ -1765,6 +1765,7 @@ config SLAB

 config SLUB
        bool "SLUB (Unqueued Allocator)"
+       select HAVE_HARDENED_USERCOPY_ALLOCATOR
        help
           SLUB is a slab allocator that minimizes cache line usage
           instead of managing queues of cached objects (SLAB approach).

diff --git a/mm/slub.c b/mm/slub.c
index 825ff4505336..7dee3d9a5843 100644
--- a/mm/slub.c
+++ b/mm/slub.c

@@ -3614,6 +3614,42 @@ void *__kmalloc_node(size_t size, gfp_t flags, int

node)
 EXPORT_SYMBOL(__kmalloc_node);
 #endif

+#ifdef CONFIG_HARDENED_USERCOPY
+/*
+ * Rejects objects that are incorrectly sized.
+ *
+ * Returns NULL if check passes, otherwise const char * to name of cache
+ * to indicate an error.
+ */
+const char *__check_heap_object(const void *ptr, unsigned long n,
+                               struct page *page)
+{
+       struct kmem_cache *s;
+       unsigned long offset;
+       size_t object_size;
+
+       /* Find object and usable object size. */
+       s = page->slab_cache;
+       object_size = slab_ksize(s);
+
+       /* Find offset within object. */
+       offset = (ptr - page_address(page)) % s->size;
+
+       /* Adjust for redzone and reject if within the redzone. */
+       if (kmem_cache_debug(s) && s->flags & SLAB_RED_ZONE) {
+               if (offset < s->red_left_pad)
+                       return s->name;
+               offset -= s->red_left_pad;
+       }
+
+       /* Allow address range falling entirely within object size. */
+       if (offset <= object_size && n <= object_size - offset)
+               return NULL;
+
+       return s->name;
+}
+#endif /* CONFIG_HARDENED_USERCOPY */
+

I compared this against what check_valid_pointer does for SLUB_DEBUG
checking. I was hoping we could utilize that function to avoid
duplication but a) __check_heap_object needs to allow accesses anywhere
in the object, not just the beginning b) accessing page->objects
is racy without the addition of locking in SLUB_DEBUG.

Still, the ptr < page_address(page) check from __check_heap_object would
be good to add to avoid generating garbage large offsets and trying to
infer C math.

diff --git a/mm/slub.c b/mm/slub.c
index 7dee3d9..5370e4f 100644
--- a/mm/slub.c
+++ b/mm/slub.c

@@ -3632,6 +3632,9 @@ const char *__check_heap_object(const void *ptr,

unsigned long n,
        s = page->slab_cache;
        object_size = slab_ksize(s);
 +       if (ptr < page_address(page))
+               return s->name;
+
        /* Find offset within object. */
        offset = (ptr - page_address(page)) % s->size;

With that, you can add

Reviwed-by: Laura Abbott [off-list ref]

Cool, I'll add that.

Should I add your reviewed-by for this patch only or for the whole series?

Thanks!

-Kees

Just this patch for now, I'm working through a couple of others

quoted

quoted

 static size_t __ksize(const void *object)
 {
        struct page *page;

Thanks,
Laura