kasan: slab: always reset the tag in get_freepointer_safe()

With CONFIG_DEBUG_PAGEALLOC enabled, the kernel should also untag the
object pointer, as done in get_freepointer().

Failing to do so reportedly leads to SLUB freelist corruptions that
manifest as boot-time crashes.

Link: https://lkml.kernel.org/r/20210514072228.534418-1-glider@google.com
Signed-off-by: Alexander Potapenko <glider@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Elliot Berman <eberman@codeaurora.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/slub.c b/mm/slub.c
index 438fa8d..3f96e09 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -301,6 +301,7 @@ static inline void *get_freepointer_safe(struct kmem_cache *s, void *object)
        if (!debug_pagealloc_enabled_static())
                return get_freepointer(s, object);
 
+       object = kasan_reset_tag(object);
        freepointer_addr = (unsigned long)object + s->offset;
        copy_from_kernel_nofault(&p, (void **)freepointer_addr, sizeof(p));
        return freelist_ptr(s, p, freepointer_addr);