kasan, slab: fix conflicts with CONFIG_HARDENED_USERCOPY

kasan, slab: fix conflicts with CONFIG_HARDENED_USERCOPY

Similarly to commit 96fedce27e13 ("kasan: make tag based mode work with
CONFIG_HARDENED_USERCOPY"), we need to reset pointer tags in
__check_heap_object() in mm/slab.c before doing any pointer math.

Link: http://lkml.kernel.org/r/9a5c0f958db10e69df5ff9f2b997866b56b7effc.1550602886.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <[email protected]>
Tested-by: Qian Cai <[email protected]>
Cc: Alexander Potapenko <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Evgeniy Stepanov <[email protected]>
Cc: Kostya Serebryany <[email protected]>
Cc: Vincenzo Frascino <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>