mm, kasan: account for object redzone in SLUB's nearest_obj()

mm, kasan: account for object redzone in SLUB's nearest_obj()

When looking up the nearest SLUB object for a given address, correctly
calculate its offset if SLAB_RED_ZONE is enabled for that cache.

Previously, when KASAN had detected an error on an object from a cache
with SLAB_RED_ZONE set, the actual start address of the object was
miscalculated, which led to random stacks having been reported.

When looking up the nearest SLUB object for a given address, correctly
calculate its offset if SLAB_RED_ZONE is enabled for that cache.

Fixes: 7ed2f9e663854db ("mm, kasan: SLAB support")
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Alexander Potapenko <[email protected]>
Cc: Andrey Konovalov <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Steven Rostedt (Red Hat) <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Kostya Serebryany <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Cc: Kuthonuzo Luruo <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>