Using the syzkaller kernel fuzzer, Andrey Konovalov generated the
following error in gadgetfs:

> BUG: KASAN: use-after-free in __lock_acquire+0x3069/0x3690
> kernel/locking/lockdep.c:3246
> Read of size 8 at addr ffff88003a2bdaf8 by task kworker/3:1/903
>
> CPU: 3 PID: 903 Comm: kworker/3:1 Not tainted 4.12.0-rc4+ #35
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> Workqueue: usb_hub_wq hub_event
> Call Trace:
>  __dump_stack lib/dump_stack.c:16 [inline]
>  dump_stack+0x292/0x395 lib/dump_stack.c:52
>  print_address_description+0x78/0x280 mm/kasan/report.c:252
>  kasan_report_error mm/kasan/report.c:351 [inline]
>  kasan_report+0x230/0x340 mm/kasan/report.c:408
>  __asan_report_load8_noabort+0x19/0x20 mm/kasan/report.c:429
>  __lock_acquire+0x3069/0x3690 kernel/locking/lockdep.c:3246
>  lock_acquire+0x22d/0x560 kernel/locking/lockdep.c:3855
>  __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
>  _raw_spin_lock+0x2f/0x40 kernel/locking/spinlock.c:151
>  spin_lock include/linux/spinlock.h:299 [inline]
>  gadgetfs_suspend+0x89/0x130 drivers/usb/gadget/legacy/inode.c:1682
>  set_link_state+0x88e/0xae0 drivers/usb/gadget/udc/dummy_hcd.c:455
>  dummy_hub_control+0xd7e/0x1fb0 drivers/usb/gadget/udc/dummy_hcd.c:2074
>  rh_call_control drivers/usb/core/hcd.c:689 [inline]
>  rh_urb_enqueue drivers/usb/core/hcd.c:846 [inline]
>  usb_hcd_submit_urb+0x92f/0x20b0 drivers/usb/core/hcd.c:1650
>  usb_submit_urb+0x8b2/0x12c0 drivers/usb/core/urb.c:542
>  usb_start_wait_urb+0x148/0x5b0 drivers/usb/core/message.c:56
>  usb_internal_control_msg drivers/usb/core/message.c:100 [inline]
>  usb_control_msg+0x341/0x4d0 drivers/usb/core/message.c:151
>  usb_clear_port_feature+0x74/0xa0 drivers/usb/core/hub.c:412
>  hub_port_disable+0x123/0x510 drivers/usb/core/hub.c:4177
>  hub_port_init+0x1ed/0x2940 drivers/usb/core/hub.c:4648
>  hub_port_connect drivers/usb/core/hub.c:4826 [inline]
>  hub_port_connect_change drivers/usb/core/hub.c:4999 [inline]
>  port_event drivers/usb/core/hub.c:5105 [inline]
>  hub_event+0x1ae1/0x3d40 drivers/usb/core/hub.c:5185
>  process_one_work+0xc08/0x1bd0 kernel/workqueue.c:2097
>  process_scheduled_works kernel/workqueue.c:2157 [inline]
>  worker_thread+0xb2b/0x1860 kernel/workqueue.c:2233
>  kthread+0x363/0x440 kernel/kthread.c:231
>  ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:424
>
> Allocated by task 9958:
>  save_stack_trace+0x1b/0x20 arch/x86/kernel/stacktrace.c:59
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:513
>  set_track mm/kasan/kasan.c:525 [inline]
>  kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:617
>  kmem_cache_alloc_trace+0x87/0x280 mm/slub.c:2745
>  kmalloc include/linux/slab.h:492 [inline]
>  kzalloc include/linux/slab.h:665 [inline]
>  dev_new drivers/usb/gadget/legacy/inode.c:170 [inline]
>  gadgetfs_fill_super+0x24f/0x540 drivers/usb/gadget/legacy/inode.c:1993
>  mount_single+0xf6/0x160 fs/super.c:1192
>  gadgetfs_mount+0x31/0x40 drivers/usb/gadget/legacy/inode.c:2019
>  mount_fs+0x9c/0x2d0 fs/super.c:1223
>  vfs_kern_mount.part.25+0xcb/0x490 fs/namespace.c:976
>  vfs_kern_mount fs/namespace.c:2509 [inline]
>  do_new_mount fs/namespace.c:2512 [inline]
>  do_mount+0x41b/0x2d90 fs/namespace.c:2834
>  SYSC_mount fs/namespace.c:3050 [inline]
>  SyS_mount+0xb0/0x120 fs/namespace.c:3027
>  entry_SYSCALL_64_fastpath+0x1f/0xbe
>
> Freed by task 9960:
>  save_stack_trace+0x1b/0x20 arch/x86/kernel/stacktrace.c:59
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:513
>  set_track mm/kasan/kasan.c:525 [inline]
>  kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:590
>  slab_free_hook mm/slub.c:1357 [inline]
>  slab_free_freelist_hook mm/slub.c:1379 [inline]
>  slab_free mm/slub.c:2961 [inline]
>  kfree+0xed/0x2b0 mm/slub.c:3882
>  put_dev+0x124/0x160 drivers/usb/gadget/legacy/inode.c:163
>  gadgetfs_kill_sb+0x33/0x60 drivers/usb/gadget/legacy/inode.c:2027
>  deactivate_locked_super+0x8d/0xd0 fs/super.c:309
>  deactivate_super+0x21e/0x310 fs/super.c:340
>  cleanup_mnt+0xb7/0x150 fs/namespace.c:1112
>  __cleanup_mnt+0x1b/0x20 fs/namespace.c:1119
>  task_work_run+0x1a0/0x280 kernel/task_work.c:116
>  exit_task_work include/linux/task_work.h:21 [inline]
>  do_exit+0x18a8/0x2820 kernel/exit.c:878
>  do_group_exit+0x14e/0x420 kernel/exit.c:982
>  get_signal+0x784/0x1780 kernel/signal.c:2318
>  do_signal+0xd7/0x2130 arch/x86/kernel/signal.c:808
>  exit_to_usermode_loop+0x1ac/0x240 arch/x86/entry/common.c:157
>  prepare_exit_to_usermode arch/x86/entry/common.c:194 [inline]
>  syscall_return_slowpath+0x3ba/0x410 arch/x86/entry/common.c:263
>  entry_SYSCALL_64_fastpath+0xbc/0xbe
>
> The buggy address belongs to the object at ffff88003a2bdae0
>  which belongs to the cache kmalloc-1024 of size 1024
> The buggy address is located 24 bytes inside of
>  1024-byte region [ffff88003a2bdae0, ffff88003a2bdee0)
> The buggy address belongs to the page:
> page:ffffea0000e8ae00 count:1 mapcount:0 mapping:          (null)
> index:0x0 compound_mapcount: 0
> flags: 0x100000000008100(slab|head)
> raw: 0100000000008100 0000000000000000 0000000000000000 0000000100170017
> raw: ffffea0000ed3020 ffffea0000f5f820 ffff88003e80efc0 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
>  ffff88003a2bd980: fb fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff88003a2bda00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> >ffff88003a2bda80: fc fc fc fc fc fc fc fc fc fc fc fc fb fb fb fb
>                                                                 ^
>  ffff88003a2bdb00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff88003a2bdb80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================

What this means is that the gadgetfs_suspend() routine was trying to
access dev->lock after it had been deallocated.  The root cause is a
race in the dummy_hcd driver; the dummy_udc_stop() routine can race
with the rest of the driver because it contains no locking.  And even
when proper locking is added, it can still race with the
set_link_state() function because that function incorrectly drops the
private spinlock before invoking any gadget driver callbacks.

The result of this race, as seen above, is that set_link_state() can
invoke a callback in gadgetfs even after gadgetfs has been unbound
from dummy_hcd's UDC and its private data structures have been
deallocated.

include/linux/usb/gadget.h documents that the ->reset, ->disconnect,
->suspend, and ->resume callbacks may be invoked in interrupt context.
In general this is necessary, to prevent races with gadget driver
removal.  This patch fixes dummy_hcd to retain the spinlock across
these calls, and it adds a spinlock acquisition to dummy_udc_stop() to
prevent the race.

The net2280 driver makes the same mistake of dropping the private
spinlock for its ->disconnect and ->reset callback invocations.  The
patch fixes it too.

Lastly, since gadgetfs_suspend() may be invoked in interrupt context,
it cannot assume that interrupts are enabled when it runs.  It must
use spin_lock_irqsave() instead of spin_lock_irq().  The patch fixes
that bug as well.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-and-tested-by: Andrey Konovalov <andreyknvl@google.com>
CC: <stable@vger.kernel.org>
Acked-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>