[PATCH AUTOSEL 3.18 28/41] cdrom: Fix race condition in cdrom_sysctl_register

Sasha Levin
2019-03-27T18:30:15Z

From: Guenter Roeck <linux@roeck-us.net>

[ Upstream commit f25191bb322dec8fa2979ecb8235643aa42470e1 ]

The following traceback is sometimes seen when booting an image in qemu:

[ 54.608293] cdrom: Uniform CD-ROM driver Revision: 3.20
[ 54.611085] Fusion MPT base driver 3.04.20
[ 54.611877] Copyright (c) 1999-2008 LSI Corporation
[ 54.616234] Fusion MPT SAS Host driver 3.04.20
[ 54.635139] sysctl duplicate entry: /dev/cdrom//info
[ 54.639578] CPU: 0 PID: 266 Comm: kworker/u4:5 Not tainted 5.0.0-rc5 #1
[ 54.639578] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
[ 54.641273] Workqueue: events_unbound async_run_entry_fn
[ 54.641273] Call Trace:
[ 54.641273] dump_stack+0x67/0x90
[ 54.641273] __register_sysctl_table+0x50b/0x570
[ 54.641273] ? rcu_read_lock_sched_held+0x6f/0x80
[ 54.641273] ? kmem_cache_alloc_trace+0x1c7/0x1f0
[ 54.646814] __register_sysctl_paths+0x1c8/0x1f0
[ 54.646814] cdrom_sysctl_register.part.7+0xc/0x5f
[ 54.646814] register_cdrom.cold.24+0x2a/0x33
[ 54.646814] sr_probe+0x4bd/0x580
[ 54.646814] ? __driver_attach+0xd0/0xd0
[ 54.646814] really_probe+0xd6/0x260
[ 54.646814] ? __driver_attach+0xd0/0xd0
[ 54.646814] driver_probe_device+0x4a/0xb0
[ 54.646814] ? __driver_attach+0xd0/0xd0
[ 54.646814] bus_for_each_drv+0x73/0xc0
[ 54.646814] __device_attach+0xd6/0x130
[ 54.646814] bus_probe_device+0x9a/0xb0
[ 54.646814] device_add+0x40c/0x670
[ 54.646814] ? __pm_runtime_resume+0x4f/0x80
[ 54.646814] scsi_sysfs_add_sdev+0x81/0x290
[ 54.646814] scsi_probe_and_add_lun+0x888/0xc00
[ 54.646814] ? scsi_autopm_get_host+0x21/0x40
[ 54.646814] __scsi_add_device+0x116/0x130
[ 54.646814] ata_scsi_scan_host+0x93/0x1c0
[ 54.646814] async_run_entry_fn+0x34/0x100
[ 54.646814] process_one_work+0x237/0x5e0
[ 54.646814] worker_thread+0x37/0x380
[ 54.646814] ? rescuer_thread+0x360/0x360
[ 54.646814] kthread+0x118/0x130
[ 54.646814] ? kthread_create_on_node+0x60/0x60
[ 54.646814] ret_from_fork+0x3a/0x50

The only sensible explanation is that cdrom_sysctl_register() is called
twice, once from the module init function and once from register_cdrom().
cdrom_sysctl_register() is not mutex protected and may happily execute
twice if the second call is made before the first call is complete.

Use a static atomic to ensure that the function is executed exactly once.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/cdrom/cdrom.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/cdrom/cdrom.c b/drivers/cdrom/cdrom.c
index 2bd91d4943e1..f4f93ca4bdad 100644
--- a/drivers/cdrom/cdrom.c
+++ b/drivers/cdrom/cdrom.c
@@ -265,6 +265,7 @@
/* #define ERRLOGMASK (CD_WARNING|CD_OPEN|CD_COUNT_TRACKS|CD_CLOSE) */
/* #define ERRLOGMASK (CD_WARNING|CD_REG_UNREG|CD_DO_IOCTL|CD_OPEN|CD_CLOSE|CD_COUNT_TRACKS) */

+#include <linux/atomic.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/major.h>
@@ -3676,9 +3677,9 @@ static struct ctl_table_header *cdrom_sysctl_header;

static void cdrom_sysctl_register(void)
{
- static int initialized;
+ static atomic_t initialized = ATOMIC_INIT(0);

- if (initialized == 1)
+ if (!atomic_add_unless(&initialized, 1, 1))
return;

cdrom_sysctl_header = register_sysctl_table(cdrom_root_table);
@@ -3689,8 +3690,6 @@ static void cdrom_sysctl_register(void)
cdrom_sysctl_settings.debug = debug;
cdrom_sysctl_settings.lock = lockdoor;
cdrom_sysctl_settings.check = check_media_type;
-
- initialized = 1;
}

static void cdrom_sysctl_unregister(void)
--
2.19.1