Re: KASAN: use-after-free Read in worker_thread (2)

[Eric Biggers]

On Sat, Nov 11, 2017 at 07:56:01AM -0800, syzbot wrote:
> syzkaller has found reproducer for the following crash on
> d9e0e63d9a6f88440eb201e1491fcf730272c706
> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached
> Raw console output is attached.
> 
> syzkaller reproducer is attached. See https://goo.gl/kgGztJ
> for information about syzkaller reproducers
> 
> 
> BUG: KASAN: use-after-free in worker_thread+0x15bb/0x1990
> kernel/workqueue.c:2244
> Read of size 8 at addr ffff88002d0e3de0 by task kworker/u8:1/1209
> 
> CPU: 0 PID: 1209 Comm: kworker/u8:1 Not tainted 4.14.0-rc8-next-20171110+
> #12
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:17 [inline]
>  dump_stack+0x194/0x257 lib/dump_stack.c:53
>  print_address_description+0x73/0x250 mm/kasan/report.c:252
>  kasan_report_error mm/kasan/report.c:351 [inline]
>  kasan_report+0x25b/0x340 mm/kasan/report.c:409
>  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
>  worker_thread+0x15bb/0x1990 kernel/workqueue.c:2244
>  kthread+0x37a/0x440 kernel/kthread.c:238
>  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:437
> 
> Allocated by task 11866:
>  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
>  kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:489
>  kmem_cache_alloc+0x12e/0x760 mm/slab.c:3548
>  kmem_cache_zalloc include/linux/slab.h:693 [inline]
>  kcm_attach net/kcm/kcmsock.c:1394 [inline]
>  kcm_attach_ioctl net/kcm/kcmsock.c:1460 [inline]
>  kcm_ioctl+0x2d1/0x1610 net/kcm/kcmsock.c:1695
>  sock_do_ioctl+0x65/0xb0 net/socket.c:960
>  sock_ioctl+0x2c2/0x440 net/socket.c:1057
>  vfs_ioctl fs/ioctl.c:46 [inline]
>  do_vfs_ioctl+0x1b1/0x1530 fs/ioctl.c:686
>  SYSC_ioctl fs/ioctl.c:701 [inline]
>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
>  entry_SYSCALL_64_fastpath+0x1f/0x96
> 
> Freed by task 11867:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:447
>  set_track mm/kasan/kasan.c:459 [inline]
>  kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
>  __cache_free mm/slab.c:3492 [inline]
>  kmem_cache_free+0x77/0x280 mm/slab.c:3750
>  kcm_unattach+0xe50/0x1510 net/kcm/kcmsock.c:1563
>  kcm_unattach_ioctl net/kcm/kcmsock.c:1608 [inline]
>  kcm_ioctl+0xdf0/0x1610 net/kcm/kcmsock.c:1705
>  sock_do_ioctl+0x65/0xb0 net/socket.c:960
>  sock_ioctl+0x2c2/0x440 net/socket.c:1057
>  vfs_ioctl fs/ioctl.c:46 [inline]
>  do_vfs_ioctl+0x1b1/0x1530 fs/ioctl.c:686
>  SYSC_ioctl fs/ioctl.c:701 [inline]
>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
>  entry_SYSCALL_64_fastpath+0x1f/0x96
> 
> The buggy address belongs to the object at ffff88002d0e3d00
>  which belongs to the cache kcm_psock_cache of size 576
> The buggy address is located 224 bytes inside of
>  576-byte region [ffff88002d0e3d00, ffff88002d0e3f40)
> The buggy address belongs to the page:
> page:ffffea0000b43880 count:1 mapcount:0 mapping:ffff88002d0e2180 index:0x0
> compound_mapcount: 0
> flags: 0x100000000008100(slab|head)
> raw: 0100000000008100 ffff88002d0e2180 0000000000000000 000000010000000b
> raw: ffffea0000b14920 ffffea0000b27e20 ffff88002b0089c0 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff88002d0e3c80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff88002d0e3d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > ffff88002d0e3d80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                                        ^
>  ffff88002d0e3e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff88002d0e3e80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================

No longer occurring, the fix seems to have been commit 7e9964574ee97:

#syz fix: kcm: Only allow TCP sockets to be attached to a KCM mux

- Eric