[media] rc: add locking to fix register/show race

When device_add is called in rc_register_device, the rc sysfs nodes show
up, and there's a window in which ir-keytable can be launched via udev
and trigger a show_protocols call, which runs without various rc_dev
fields filled in yet. Add some locking around registration and
store/show_protocols to prevent that from happening.

The problem manifests thusly:

[64692.957872] BUG: unable to handle kernel NULL pointer dereference at 0000000000000090
[64692.957878] IP: [<ffffffffa036a4c1>] show_protocols+0x47/0xf1 [rc_core]
[64692.957890] PGD 19cfc7067 PUD 19cfc6067 PMD 0
[64692.957894] Oops: 0000 [#1] SMP
[64692.957897] last sysfs file: /sys/devices/pci0000:00/0000:00:03.1/usb3/3-1/3-1:1.0/rc/rc2/protocols
[64692.957902] CPU 3
[64692.957903] Modules linked in: redrat3(+) ir_lirc_codec lirc_dev ir_sony_decoder ir_jvc_decoder ir_rc6_decoder ir_rc5_decoder rc_hauppauge ir_nec
_decoder rc_core ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_filter ip6_tables snd_emu10k1_synth snd_emux_synth snd_seq_virmidi snd_seq_mi
di_event snd_seq_midi_emul snd_emu10k1 snd_rawmidi snd_ac97_codec ac97_bus snd_seq snd_pcm snd_seq_device snd_timer snd_page_alloc snd_util_mem pcsp
kr tg3 snd_hwdep emu10k1_gp snd amd64_edac_mod gameport edac_core soundcore edac_mce_amd k8temp shpchp i2c_piix4 lm63 e100 mii uinput ipv6 raid0 rai
d1 ata_generic firewire_ohci pata_acpi firewire_core crc_itu_t sata_svw pata_serverworks floppy radeon ttm drm_kms_helper drm i2c_algo_bit i2c_core
[last unloaded: redrat3]
[64692.957949] [64692.957952] Pid: 12265, comm: ir-keytable Tainted: G   M    W   2.6.39-rc6+ #2 empty empty/TYAN Thunder K8HM S3892
[64692.957957] RIP: 0010:[<ffffffffa036a4c1>]  [<ffffffffa036a4c1>] show_protocols+0x47/0xf1 [rc_core]
[64692.957962] RSP: 0018:ffff880194509e38  EFLAGS: 00010202
[64692.957964] RAX: 0000000000000000 RBX: ffffffffa036d1e0 RCX: ffffffffa036a47a
[64692.957966] RDX: ffff88019a84d000 RSI: ffffffffa036d1e0 RDI: ffff88019cf2f3f0
[64692.957969] RBP: ffff880194509e68 R08: 0000000000000002 R09: 0000000000000000
[64692.957971] R10: 0000000000000002 R11: 0000000000001617 R12: ffff88019a84d000
[64692.957973] R13: 0000000000001000 R14: ffff8801944d2e38 R15: ffff88019ce5f190
[64692.957976] FS:  00007f0a30c9a720(0000) GS:ffff88019fc00000(0000) knlGS:0000000000000000
[64692.957979] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[64692.957981] CR2: 0000000000000090 CR3: 000000019a8e0000 CR4: 00000000000006e0
[64692.957983] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[64692.957986] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[64692.957989] Process ir-keytable (pid: 12265, threadinfo ffff880194508000, task ffff88019a9fc720)
[64692.957991] Stack:
[64692.957992]  0000000000000002 ffffffffa036d1e0 ffff880194509f58 0000000000001000
[64692.957997]  ffff8801944d2e38 ffff88019ce5f190 ffff880194509e98 ffffffff8131484b
[64692.958001]  ffffffff8118e923 ffffffff810e9b2f ffff880194509e98 ffff8801944d2e18
[64692.958005] Call Trace:
[64692.958014]  [<ffffffff8131484b>] dev_attr_show+0x27/0x4e
[64692.958014]  [<ffffffff8118e923>] ? sysfs_read_file+0x94/0x172
[64692.958014]  [<ffffffff810e9b2f>] ? __get_free_pages+0x16/0x52
[64692.958014]  [<ffffffff8118e94c>] sysfs_read_file+0xbd/0x172
[64692.958014]  [<ffffffff8113205e>] vfs_read+0xac/0xf3
[64692.958014]  [<ffffffff8113347b>] ? fget_light+0x3a/0xa1
[64692.958014]  [<ffffffff811320f2>] sys_read+0x4d/0x74
[64692.958014]  [<ffffffff814c19c2>] system_call_fastpath+0x16/0x1b

Its a bit difficult to reproduce, but I'm fairly confident this has
fixed the problem.
Signed-off-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/rc/rc-main.c

@@ -749,6 +749,9 @@ static struct {
  * it is trigged by reading /sys/class/rc/rc?/protocols.
  * It returns the protocol names of supported protocols.
  * Enabled protocols are printed in brackets.
+ *
+ * dev->lock is taken to guard against races between device
+ * registration, store_protocols and show_protocols.
  */
 static ssize_t show_protocols(struct device *device,
 			      struct device_attribute *mattr, char *buf)
@@ -762,6 +765,8 @@ static ssize_t show_protocols(struct device *device,
 	if (!dev)
 		return -EINVAL;
 
+	mutex_lock(&dev->lock);
+
 	if (dev->driver_type == RC_DRIVER_SCANCODE) {
 		enabled = dev->rc_map.rc_type;
 		allowed = dev->allowed_protos;
@@ -784,6 +789,9 @@ static ssize_t show_protocols(struct device *device,
 	if (tmp != buf)
 		tmp--;
 	*tmp = '\n';
+
+	mutex_unlock(&dev->lock);
+
 	return tmp + 1 - buf;
 }
 
@@ -802,6 +810,9 @@ static ssize_t show_protocols(struct device *device,
  * Writing "none" will disable all protocols.
  * Returns -EINVAL if an invalid protocol combination or unknown protocol name
  * is used, otherwise @len.
+ *
+ * dev->lock is taken to guard against races between device
+ * registration, store_protocols and show_protocols.
  */
 static ssize_t store_protocols(struct device *device,
 			       struct device_attribute *mattr,
@@ -815,18 +826,22 @@ static ssize_t store_protocols(struct device *device,
 	u64 mask;
 	int rc, i, count = 0;
 	unsigned long flags;
+	ssize_t ret;
 
 	/* Device is being removed */
 	if (!dev)
 		return -EINVAL;
 
+	mutex_lock(&dev->lock);
+
 	if (dev->driver_type == RC_DRIVER_SCANCODE)
 		type = dev->rc_map.rc_type;
 	else if (dev->raw)
 		type = dev->raw->enabled_protocols;
 	else {
 		IR_dprintk(1, "Protocol switching not supported\n");
-		return -EINVAL;
+		ret = -EINVAL;
+		goto out;
 	}
 
 	while ((tmp = strsep((char **) &data, " \n")) != NULL) {
@@ -860,7 +875,8 @@ static ssize_t store_protocols(struct device *device,
 			}
 			if (i == ARRAY_SIZE(proto_names)) {
 				IR_dprintk(1, "Unknown protocol: '%s'\n", tmp);
-				return -EINVAL;
+				ret = -EINVAL;
+				goto out;
 			}
 			count++;
 		}
@@ -875,7 +891,8 @@ static ssize_t store_protocols(struct device *device,
 
 	if (!count) {
 		IR_dprintk(1, "Protocol not specified\n");
-		return -EINVAL;
+		ret = -EINVAL;
+		goto out;
 	}
 
 	if (dev->change_protocol) {
@@ -883,7 +900,8 @@ static ssize_t store_protocols(struct device *device,
 		if (rc < 0) {
 			IR_dprintk(1, "Error setting protocols to 0x%llx\n",
 				   (long long)type);
-			return -EINVAL;
+			ret = -EINVAL;
+			goto out;
 		}
 	}
 
@@ -898,7 +916,11 @@ static ssize_t store_protocols(struct device *device,
 	IR_dprintk(1, "Current protocol(s): 0x%llx\n",
 		   (long long)type);
 
-	return len;
+	ret = len;
+
+out:
+	mutex_unlock(&dev->lock);
+	return ret;
 }
 
 static void rc_dev_release(struct device *device)
@@ -974,6 +996,7 @@ struct rc_dev *rc_allocate_device(void)
 
 	spin_lock_init(&dev->rc_map.lock);
 	spin_lock_init(&dev->keylock);
+	mutex_init(&dev->lock);
 	setup_timer(&dev->timer_keyup, ir_timer_keyup, (unsigned long)dev);
 
 	dev->dev.type = &rc_dev_type;
@@ -1019,12 +1042,21 @@ int rc_register_device(struct rc_dev *dev)
 	if (dev->close)
 		dev->input_dev->close = ir_close;
 
+	/*
+	 * Take the lock here, as the device sysfs node will appear
+	 * when device_add() is called, which may trigger an ir-keytable udev
+	 * rule, which will in turn call show_protocols and access either
+	 * dev->rc_map.rc_type or dev->raw->enabled_protocols before it has
+	 * been initialized.
+	 */
+	mutex_lock(&dev->lock);
+
 	dev->devno = (unsigned long)(atomic_inc_return(&devno) - 1);
 	dev_set_name(&dev->dev, "rc%ld", dev->devno);
 	dev_set_drvdata(&dev->dev, dev);
 	rc = device_add(&dev->dev);
 	if (rc)
-		return rc;
+		goto out_unlock;
 
 	rc = ir_setkeytable(dev, rc_map);
 	if (rc)
@@ -1058,6 +1090,7 @@ int rc_register_device(struct rc_dev *dev)
 		if (rc < 0)
 			goto out_input;
 	}
+	mutex_unlock(&dev->lock);
 
 	if (dev->change_protocol) {
 		rc = dev->change_protocol(dev, rc_map->rc_type);
@@ -1083,6 +1116,8 @@ int rc_register_device(struct rc_dev *dev)
 	ir_free_table(&dev->rc_map);
 out_dev:
 	device_del(&dev->dev);
+out_unlock:
+	mutex_unlock(&dev->lock);
 	return rc;
 }
 EXPORT_SYMBOL_GPL(rc_register_device);

include/media/rc-core.h

@@ -40,6 +40,8 @@ enum rc_driver_type {
  * @driver_name: name of the hardware driver which registered this device
  * @map_name: name of the default keymap
  * @rc_map: current scan/key table
+ * @lock: used to ensure we've filled in all protocol details before
+ *	anyone can call show_protocols or store_protocols
  * @devno: unique remote control device number
  * @raw: additional data for raw pulse/space devices
  * @input_dev: the input child device used to communicate events to userspace
@@ -87,6 +89,7 @@ struct rc_dev {
 	char				*driver_name;
 	const char			*map_name;
 	struct rc_map			rc_map;
+	struct mutex			lock;
 	unsigned long			devno;
 	struct ir_raw_event_ctrl	*raw;
 	struct input_dev		*input_dev;