Re: KASAN: use-after-free Read in get_work_pool

[Cong Wang]

On Thu, Oct 26, 2017 at 11:00 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
> On Thu, Oct 26, 2017 at 7:58 PM, Tejun Heo <tj@xxxxxxxxxx> wrote:
>> Hello,
>>
>> On Thu, Oct 26, 2017 at 09:35:44AM -0700, syzbot wrote:
>>> BUG: KASAN: use-after-free in __read_once_size
>>> include/linux/compiler.h:276 [inline]
>>> BUG: KASAN: use-after-free in atomic64_read
>>> arch/x86/include/asm/atomic64_64.h:21 [inline]
>>> BUG: KASAN: use-after-free in atomic_long_read
>>> include/asm-generic/atomic-long.h:44 [inline]
>>> BUG: KASAN: use-after-free in get_work_pool+0x1c2/0x1e0
>>> kernel/workqueue.c:709
>>> Read of size 8 at addr ffff8801cc58c378 by task syz-executor5/21326
>>>
>>> CPU: 1 PID: 21326 Comm: syz-executor5 Not tainted 4.13.0+ #43
>>> Hardware name: Google Google Compute Engine/Google Compute Engine,
>>> BIOS Google 01/01/2011
>>> Call Trace:
>>>  __dump_stack lib/dump_stack.c:16 [inline]
>>>  dump_stack+0x194/0x257 lib/dump_stack.c:52
>>>  print_address_description+0x73/0x250 mm/kasan/report.c:252
>>>  kasan_report_error mm/kasan/report.c:351 [inline]
>>>  kasan_report+0x24e/0x340 mm/kasan/report.c:409
>>>  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
>>>  __read_once_size include/linux/compiler.h:276 [inline]
>>>  atomic64_read arch/x86/include/asm/atomic64_64.h:21 [inline]
>>>  atomic_long_read include/asm-generic/atomic-long.h:44 [inline]
>>>  get_work_pool+0x1c2/0x1e0 kernel/workqueue.c:709
>>>  __queue_work+0x235/0x1150 kernel/workqueue.c:1401
>>>  queue_work_on+0x16a/0x1c0 kernel/workqueue.c:1486
>>>  queue_work include/linux/workqueue.h:489 [inline]
>>>  strp_check_rcv+0x25/0x30 net/strparser/strparser.c:553
>>>  kcm_attach net/kcm/kcmsock.c:1439 [inline]
>>>  kcm_attach_ioctl net/kcm/kcmsock.c:1460 [inline]
>>>  kcm_ioctl+0x826/0x1610 net/kcm/kcmsock.c:1695
>>>  sock_do_ioctl+0x65/0xb0 net/socket.c:961
>>>  sock_ioctl+0x2c2/0x440 net/socket.c:1058
>>>  vfs_ioctl fs/ioctl.c:45 [inline]
>>>  do_vfs_ioctl+0x1b1/0x1530 fs/ioctl.c:685
>>>  SYSC_ioctl fs/ioctl.c:700 [inline]
>>>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
>>>  entry_SYSCALL_64_fastpath+0x1f/0xbe
>>
>> Looks like kcm is trying to reuse a work item whose last workqueue has
>> been destroyed without re-initing it.  A work item needs to be
>> reinit'd.
>
> +kcm maintainers

Can you try the fix below? There is no C reproducer so I can't verify it.

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index af4e76ac88ff..7816f44c576a 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -1433,11 +1433,12 @@ static int kcm_attach(struct socket *sock,
struct socket *csock,
        KCM_STATS_INCR(mux->stats.psock_attach);
        mux->psocks_cnt++;
        psock_now_avail(psock);
-       spin_unlock_bh(&mux->lock);

        /* Schedule RX work in case there are already bytes queued */
        strp_check_rcv(&psock->strp);

+       spin_unlock_bh(&mux->lock);
+
        return 0;
 }