From: Walter Wu <walter-zh.wu@xxxxxxxxxxxx> Subject: kasan: fix null pointer dereference in kasan_record_aux_stack Syzbot reported the following [1]: BUG: kernel NULL pointer dereference, address: 0000000000000008 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 2d993067 P4D 2d993067 PUD 19a3c067 PMD 0 Oops: 0000 [#1] PREEMPT SMP KASAN CPU: 1 PID: 3852 Comm: kworker/1:2 Not tainted 5.10.0-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Workqueue: events free_ipc RIP: 0010:kasan_record_aux_stack+0x77/0xb0 Add null checking slab object from kasan_get_alloc_meta() in order to avoid null pointer dereference. [1] https://syzkaller.appspot.com/x/log.txt?x=10a82a50d00000 Link: https://lkml.kernel.org/r/20201228080018.23041-1-walter-zh.wu@xxxxxxxxxxxx Signed-off-by: Walter Wu <walter-zh.wu@xxxxxxxxxxxx> Suggested-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Cc: Alexander Potapenko <glider@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/kasan/generic.c | 2 ++ 1 file changed, 2 insertions(+) --- a/mm/kasan/generic.c~kasan-fix-null-pointer-dereference-in-kasan_record_aux_stack +++ a/mm/kasan/generic.c @@ -337,6 +337,8 @@ void kasan_record_aux_stack(void *addr) cache = page->slab_cache; object = nearest_obj(cache, page, addr); alloc_meta = kasan_get_alloc_meta(cache, object); + if (!alloc_meta) + return; alloc_meta->aux_stack[1] = alloc_meta->aux_stack[0]; alloc_meta->aux_stack[0] = kasan_save_stack(GFP_NOWAIT); _
