From: Alexander Potapenko <glider@xxxxxxxxxx> Subject: 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@xxxxxxxxxx Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx> Cc: Marco Elver <elver@xxxxxxxxxx> Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx> Cc: Elliot Berman <eberman@xxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/slub.c | 1 + 1 file changed, 1 insertion(+) --- a/mm/slub.c~kasan-slab-always-reset-the-tag-in-get_freepointer_safe +++ a/mm/slub.c @@ -301,6 +301,7 @@ static inline void *get_freepointer_safe 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); _
