Re: BUG: unable to handle kernel NULL pointer dereference

[Eric Biggers]

On Sun, Dec 03, 2017 at 04:37:01AM -0800, syzbot wrote:
> BUG: KASAN: use-after-free in skcipher_request_set_tfm
> include/crypto/skcipher.h:499 [inline]
> BUG: KASAN: use-after-free in crypto_aead_copy_sgl crypto/algif_aead.c:85
> [inline]
> BUG: KASAN: use-after-free in _aead_recvmsg crypto/algif_aead.c:210 [inline]
> BUG: KASAN: use-after-free in aead_recvmsg+0x1552/0x1970
> crypto/algif_aead.c:313
> Read of size 4 at addr ffff8801cabcfd9c by task syzkaller687795/3634
[...]
> Allocated by task 3442:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:447
>  set_track mm/kasan/kasan.c:459 [inline]
>  kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
>  __do_kmalloc mm/slab.c:3711 [inline]
>  __kmalloc+0x162/0x760 mm/slab.c:3720
>  kmalloc include/linux/slab.h:504 [inline]
>  kzalloc include/linux/slab.h:688 [inline]
>  crypto_create_tfm+0x82/0x2e0 crypto/api.c:455
>  crypto_alloc_tfm+0x10e/0x2f0 crypto/api.c:540
>  crypto_alloc_skcipher+0x2c/0x40 crypto/skcipher.c:926
>  crypto_get_default_null_skcipher+0x5f/0x80 crypto/crypto_null.c:164
>  crypto_get_default_null_skcipher2 include/crypto/null.h:17 [inline]
>  aead_bind+0x89/0x140 crypto/algif_aead.c:472
>  alg_bind+0x1ab/0x440 crypto/af_alg.c:179
>  SYSC_bind+0x1b4/0x3f0 net/socket.c:1475
>  SyS_bind+0x24/0x30 net/socket.c:1461
>  entry_SYSCALL_64_fastpath+0x1f/0x96

#syz dup: KASAN: use-after-free Read in aead_recvmsg