aio: take an extra file reference before call vfs_poll()

euler inclusion
category: bugfix
bugzilla: 10714
CVE: NA
--------------------------------------------------

Taking an extra file reference before call vfs_poll(), else
the file may be released by aio_poll_wake() if an expected
event is triggered immediately (e.g., by the close of a
pair of pipes) after the return of vfs_poll(), and we may
hit a use-after-free splat as shown below:

 BUG: KASAN: use-after-free in perf_trace_lock_acquire+0x3ab/0x570
 Read of size 8 at addr ffff888379bfd4b0 by task syz-executor.1/4953

 CPU: 0 PID: 4953 Comm: syz-executor.1 Not tainted 4.19.24
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1
 Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0xca/0x13e lib/dump_stack.c:113
  print_address_description+0x79/0x330 mm/kasan/report.c:256
  kasan_report_error mm/kasan/report.c:354 [inline]
  kasan_report+0x18a/0x2e0 mm/kasan/report.c:412
  trace_event_get_offsets_lock_acquire include/trace/events/lock.h:13 [inline]
  perf_trace_lock_acquire+0x3ab/0x570 include/trace/events/lock.h:13
  trace_lock_acquire include/trace/events/lock.h:13 [inline]
  lock_acquire+0x202/0x310 kernel/locking/lockdep.c:3899
  __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
  _raw_spin_lock+0x2c/0x40 kernel/locking/spinlock.c:144
  spin_lock include/linux/spinlock.h:329 [inline]
  aio_poll fs/aio.c:1750 [inline]
  io_submit_one+0xb90/0x1b30 fs/aio.c:1853
  __do_sys_io_submit fs/aio.c:1919 [inline]
  __se_sys_io_submit fs/aio.c:1890 [inline]
  __x64_sys_io_submit+0x19b/0x500 fs/aio.c:1890
  do_syscall_64+0xc8/0x580 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
  ......
  Allocated by task 4953:
  set_track mm/kasan/kasan.c:460 [inline]
  kasan_kmalloc+0xa0/0xd0 mm/kasan/kasan.c:553
  kmem_cache_alloc_trace+0x12f/0x2d0 mm/slub.c:2733
  kmalloc include/linux/slab.h:513 [inline]
  kzalloc include/linux/slab.h:707 [inline]
  alloc_pipe_info+0xdf/0x410 fs/pipe.c:633
  get_pipe_inode fs/pipe.c:712 [inline]
  create_pipe_files+0x98/0x780 fs/pipe.c:744
  __do_pipe_flags+0x35/0x230 fs/pipe.c:781
  do_pipe2+0x87/0x150 fs/pipe.c:829
  __do_sys_pipe2 fs/pipe.c:847 [inline]
  __se_sys_pipe2 fs/pipe.c:845 [inline]
  __x64_sys_pipe2+0x55/0x80 fs/pipe.c:845
  do_syscall_64+0xc8/0x580 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

 Freed by task 4952:
  set_track mm/kasan/kasan.c:460 [inline]
  __kasan_slab_free+0x12e/0x180 mm/kasan/kasan.c:521
  slab_free_hook mm/slub.c:1371 [inline]
  slab_free_freelist_hook mm/slub.c:1398 [inline]
  slab_free mm/slub.c:2953 [inline]
  kfree+0xeb/0x2f0 mm/slub.c:3906
  put_pipe_info+0xb0/0xd0 fs/pipe.c:556
  pipe_release+0x1ab/0x240 fs/pipe.c:577
  __fput+0x27f/0x7f0 fs/file_table.c:278
  task_work_run+0x136/0x1b0 kernel/task_work.c:113
  tracehook_notify_resume include/linux/tracehook.h:193 [inline]
  exit_to_usermode_loop+0x1a7/0x1d0 arch/x86/entry/common.c:166
  prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
  syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
  do_syscall_64+0x461/0x580 arch/x86/entry/common.c:293
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

Link: https://www.spinics.net/lists/linux-fsdevel/msg140360.html
Fixes: bfe4037e ("aio: implement IOCB_CMD_POLL")
Cc: stable@vger.kernel.org [4.19+]
Signed-off-by: NHou Tao <houtao1@huawei.com>
Reviewed-by: NMiao Xie <miaoxie@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

fs/aio.c

@@ -1740,6 +1740,12 @@ static ssize_t aio_poll(struct aio_kiocb *aiocb, struct iocb *iocb)
 	/* one for removal from waitqueue, one for this function */
 	refcount_set(&aiocb->ki_refcnt, 2);
 
+	/*
+	 * file may be released by aio_poll_wake() if an expected event
+	 * is triggered immediately after the return of vfs_poll(), so
+	 * an extra reference is needed here to prevent use-after-free.
+	 */
+	get_file(req->file);
 	mask = vfs_poll(req->file, &apt.pt) & req->events;
 	if (unlikely(!req->head)) {
 		/* we did not manage to set up a waitqueue, done */
@@ -1765,6 +1771,8 @@ static ssize_t aio_poll(struct aio_kiocb *aiocb, struct iocb *iocb)
 	spin_unlock_irq(&ctx->ctx_lock);
 
 out:
+	/* release the extra reference for vfs_poll() */
+	fput(req->file);
 	if (unlikely(apt.error)) {
 		fput(req->file);
 		return apt.error;