[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>

1 files changed, 41 insertions, 6 deletions

diff --git a/drivers/media/rc/rc-main.c b/drivers/media/rc/rc-main.c
index a2706648e365..0d4fcd911b8c 100644
--- a/drivers/media/rc/rc-main.c
+++ b/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 @@ out_table:
         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);