releases/4.14.111/cdrom-fix-race-condition-in-cdrom_sysctl_register.patch

   1 From 8737b6e883ba9693d6fad2ec753df0922facd171 Mon Sep 17 00:00:00 2001
   2 From: Guenter Roeck <linux@roeck-us.net>
   3 Date: Wed, 6 Feb 2019 21:13:49 -0800
   4 Subject: cdrom: Fix race condition in cdrom_sysctl_register
   5
   6 [ Upstream commit f25191bb322dec8fa2979ecb8235643aa42470e1 ]
   7
   8 The following traceback is sometimes seen when booting an image in qemu:
   9
  10 [   54.608293] cdrom: Uniform CD-ROM driver Revision: 3.20
  11 [   54.611085] Fusion MPT base driver 3.04.20
  12 [   54.611877] Copyright (c) 1999-2008 LSI Corporation
  13 [   54.616234] Fusion MPT SAS Host driver 3.04.20
  14 [   54.635139] sysctl duplicate entry: /dev/cdrom//info
  15 [   54.639578] CPU: 0 PID: 266 Comm: kworker/u4:5 Not tainted 5.0.0-rc5 #1
  16 [   54.639578] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
  17 [   54.641273] Workqueue: events_unbound async_run_entry_fn
  18 [   54.641273] Call Trace:
  19 [   54.641273]  dump_stack+0x67/0x90
  20 [   54.641273]  __register_sysctl_table+0x50b/0x570
  21 [   54.641273]  ? rcu_read_lock_sched_held+0x6f/0x80
  22 [   54.641273]  ? kmem_cache_alloc_trace+0x1c7/0x1f0
  23 [   54.646814]  __register_sysctl_paths+0x1c8/0x1f0
  24 [   54.646814]  cdrom_sysctl_register.part.7+0xc/0x5f
  25 [   54.646814]  register_cdrom.cold.24+0x2a/0x33
  26 [   54.646814]  sr_probe+0x4bd/0x580
  27 [   54.646814]  ? __driver_attach+0xd0/0xd0
  28 [   54.646814]  really_probe+0xd6/0x260
  29 [   54.646814]  ? __driver_attach+0xd0/0xd0
  30 [   54.646814]  driver_probe_device+0x4a/0xb0
  31 [   54.646814]  ? __driver_attach+0xd0/0xd0
  32 [   54.646814]  bus_for_each_drv+0x73/0xc0
  33 [   54.646814]  __device_attach+0xd6/0x130
  34 [   54.646814]  bus_probe_device+0x9a/0xb0
  35 [   54.646814]  device_add+0x40c/0x670
  36 [   54.646814]  ? __pm_runtime_resume+0x4f/0x80
  37 [   54.646814]  scsi_sysfs_add_sdev+0x81/0x290
  38 [   54.646814]  scsi_probe_and_add_lun+0x888/0xc00
  39 [   54.646814]  ? scsi_autopm_get_host+0x21/0x40
  40 [   54.646814]  __scsi_add_device+0x116/0x130
  41 [   54.646814]  ata_scsi_scan_host+0x93/0x1c0
  42 [   54.646814]  async_run_entry_fn+0x34/0x100
  43 [   54.646814]  process_one_work+0x237/0x5e0
  44 [   54.646814]  worker_thread+0x37/0x380
  45 [   54.646814]  ? rescuer_thread+0x360/0x360
  46 [   54.646814]  kthread+0x118/0x130
  47 [   54.646814]  ? kthread_create_on_node+0x60/0x60
  48 [   54.646814]  ret_from_fork+0x3a/0x50
  49
  50 The only sensible explanation is that cdrom_sysctl_register() is called
  51 twice, once from the module init function and once from register_cdrom().
  52 cdrom_sysctl_register() is not mutex protected and may happily execute
  53 twice if the second call is made before the first call is complete.
  54
  55 Use a static atomic to ensure that the function is executed exactly once.
  56
  57 Signed-off-by: Guenter Roeck <linux@roeck-us.net>
  58 Signed-off-by: Jens Axboe <axboe@kernel.dk>
  59 Signed-off-by: Sasha Levin <sashal@kernel.org>
  60 ---
  61  drivers/cdrom/cdrom.c | 7 +++----
  62  1 file changed, 3 insertions(+), 4 deletions(-)
  63
  64 diff --git a/drivers/cdrom/cdrom.c b/drivers/cdrom/cdrom.c
  65 index 930b49606a8c..ea6558d4864c 100644
  66 --- a/drivers/cdrom/cdrom.c
  67 +++ b/drivers/cdrom/cdrom.c
  68 @@ -265,6 +265,7 @@
  69  /* #define ERRLOGMASK (CD_WARNING|CD_OPEN|CD_COUNT_TRACKS|CD_CLOSE) */
  70  /* #define ERRLOGMASK (CD_WARNING|CD_REG_UNREG|CD_DO_IOCTL|CD_OPEN|CD_CLOSE|CD_COUNT_TRACKS) */
  71
  72 +#include <linux/atomic.h>
  73  #include <linux/module.h>
  74  #include <linux/fs.h>
  75  #include <linux/major.h>
  76 @@ -3689,9 +3690,9 @@ static struct ctl_table_header *cdrom_sysctl_header;
  77
  78  static void cdrom_sysctl_register(void)
  79  {
  80 -       static int initialized;
  81 +       static atomic_t initialized = ATOMIC_INIT(0);
  82
  83 -       if (initialized == 1)
  84 +       if (!atomic_add_unless(&initialized, 1, 1))
  85                 return;
  86
  87         cdrom_sysctl_header = register_sysctl_table(cdrom_root_table);
  88 @@ -3702,8 +3703,6 @@ static void cdrom_sysctl_register(void)
  89         cdrom_sysctl_settings.debug = debug;
  90         cdrom_sysctl_settings.lock = lockdoor;
  91         cdrom_sysctl_settings.check = check_media_type;
  92 -
  93 -       initialized = 1;
  94  }
  95
  96  static void cdrom_sysctl_unregister(void)
  97 --
  98 2.19.1
  99