pty: Fix BUG()s when ptmx_open() errors out

If pmtx_open() fails to get a slave inode or fails the pty_open(),
the tty is released as part of the error cleanup. As evidenced by the
first BUG stacktrace below, pty_close() assumes that the linked pty has
a valid, initialized inode* stored in driver_data.

Also, as evidenced by the second BUG stacktrace below, pty_unix98_shutdown()
assumes that the master pty's driver_data has been initialized.

1) Fix the invalid assumption in pty_close().
2) Initialize driver_data immediately so proper devpts fs cleanup occurs.

Fixes this BUG:

[  815.868844] BUG: unable to handle kernel NULL pointer dereference at 0000000000000028
[  815.869018] IP: [<ffffffff81207bcc>] devpts_pty_kill+0x1c/0xa0
[  815.869190] PGD 7c775067 PUD 79deb067 PMD 0
[  815.869315] Oops: 0000 [#1] PREEMPT SMP
[  815.869443] Modules linked in: kvm_intel kvm snd_hda_intel snd_hda_codec snd_hwdep snd_pcm snd_seq_midi microcode snd_rawmidi psmouse serio_raw snd_seq_midi_event snd_seq snd_timer$
[  815.870025] CPU 0
[  815.870143] Pid: 27819, comm: stress_test_tty Tainted: G        W    3.8.0-next-20130125+ttypatch-2-xeon #2 Bochs Bochs
[  815.870386] RIP: 0010:[<ffffffff81207bcc>]  [<ffffffff81207bcc>] devpts_pty_kill+0x1c/0xa0
[  815.870540] RSP: 0018:ffff88007d3e1ac8  EFLAGS: 00010282
[  815.870661] RAX: ffff880079c20800 RBX: 0000000000000000 RCX: 0000000000000000
[  815.870804] RDX: ffff880079c209a8 RSI: 0000000000000286 RDI: 0000000000000000
[  815.870933] RBP: ffff88007d3e1ae8 R08: 0000000000000000 R09: 0000000000000000
[  815.871078] R10: 0000000000000000 R11: 0000000000000001 R12: ffff88007bfb7e00
[  815.871209] R13: 0000000000000005 R14: ffff880079c20c00 R15: ffff880079c20c00
[  815.871343] FS:  00007f2e86206700(0000) GS:ffff88007fc00000(0000) knlGS:0000000000000000
[  815.871495] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[  815.871617] CR2: 0000000000000028 CR3: 000000007ae56000 CR4: 00000000000006f0
[  815.871752] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  815.871902] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[  815.872012] Process stress_test_tty (pid: 27819, threadinfo ffff88007d3e0000, task ffff88007c874530)
[  815.872012] Stack:
[  815.872012]  ffff88007bfb7e00 ffff880079c20c00 ffff88007bfb7e00 0000000000000005
[  815.872012]  ffff88007d3e1b08 ffffffff81417be7 ffff88007caa9bd8 ffff880079c20800
[  815.872012]  ffff88007d3e1bc8 ffffffff8140e5f8 0000000000000000 0000000000000000
[  815.872012] Call Trace:
[  815.872012]  [<ffffffff81417be7>] pty_close+0x157/0x170
[  815.872012]  [<ffffffff8140e5f8>] tty_release+0x138/0x580
[  815.872012]  [<ffffffff816d29f3>] ? _raw_spin_lock+0x23/0x30
[  815.872012]  [<ffffffff816d267a>] ? _raw_spin_unlock+0x1a/0x40
[  815.872012]  [<ffffffff816d0178>] ? __mutex_unlock_slowpath+0x48/0x60
[  815.872012]  [<ffffffff81417dff>] ptmx_open+0x11f/0x180
[  815.872012]  [<ffffffff8119394b>] chrdev_open+0x9b/0x1c0
[  815.872012]  [<ffffffff8118d643>] do_dentry_open+0x203/0x290
[  815.872012]  [<ffffffff811938b0>] ? cdev_put+0x30/0x30
[  815.872012]  [<ffffffff8118d705>] finish_open+0x35/0x50
[  815.872012]  [<ffffffff8119dcce>] do_last+0x6fe/0xe90
[  815.872012]  [<ffffffff8119a7af>] ? link_path_walk+0x7f/0x880
[  815.872012]  [<ffffffff810909d5>] ? cpuacct_charge+0x75/0x80
[  815.872012]  [<ffffffff8119e51c>] path_openat+0xbc/0x4e0
[  815.872012]  [<ffffffff816d0fd0>] ? __schedule+0x400/0x7f0
[  815.872012]  [<ffffffff8140e956>] ? tty_release+0x496/0x580
[  815.872012]  [<ffffffff8119ec11>] do_filp_open+0x41/0xa0
[  815.872012]  [<ffffffff816d267a>] ? _raw_spin_unlock+0x1a/0x40
[  815.872012]  [<ffffffff811abe39>] ? __alloc_fd+0xe9/0x140
[  815.872012]  [<ffffffff8118ea44>] do_sys_open+0xf4/0x1e0
[  815.872012]  [<ffffffff8118eb51>] sys_open+0x21/0x30
[  815.872012]  [<ffffffff816da499>] system_call_fastpath+0x16/0x1b
[  815.872012] Code: 0f 1f 80 00 00 00 00 45 31 e4 eb d7 0f 0b 90 0f 1f 44 00 00 55 48 89 e5 48 83 ec 20 48 89 5d e8 48 89 fb 4c 89 65 f0 4c 89 6d f8 <48> 8b 47 28 48 81 78 58 d1 1c 0$
[  815.872012] RIP  [<ffffffff81207bcc>] devpts_pty_kill+0x1c/0xa0
[  815.872012]  RSP <ffff88007d3e1ac8>
[  815.872012] CR2: 0000000000000028
[  815.897036] ---[ end trace eadf50b7f34e47d5 ]---

Fixes this BUG also:

[  608.366836] BUG: unable to handle kernel NULL pointer dereference at 0000000000000028
[  608.366948] IP: [<ffffffff812078d8>] devpts_kill_index+0x18/0x70
[  608.367050] PGD 7c75b067 PUD 7b919067 PMD 0
[  608.367135] Oops: 0000 [#1] PREEMPT SMP
[  608.367201] Modules linked in: kvm_intel kvm snd_hda_intel snd_hda_codec snd_hwdep snd_pcm snd_seq_midi snd_rawmidi snd_seq_midi_event microcode snd_seq psmouse snd_timer snd_seq_device serio_raw snd mac_hid soundcore snd_page_alloc rfcomm virtio_balloon parport_pc bnep bluetooth ppdev i2c_piix4 lp parport floppy
[  608.367617] CPU 2
[  608.367669] Pid: 1918, comm: stress_test_tty Tainted: G        W    3.8.0-next-20130125+ttypatch-2-xeon #2 Bochs Bochs
[  608.367796] RIP: 0010:[<ffffffff812078d8>]  [<ffffffff812078d8>] devpts_kill_index+0x18/0x70
[  608.367885] RSP: 0018:ffff88007ae41a88  EFLAGS: 00010286
[  608.367951] RAX: ffffffff81417e80 RBX: ffff880036472400 RCX: 0000000180400028
[  608.368010] RDX: ffff880036470004 RSI: 0000000000000004 RDI: 0000000000000000
[  608.368010] RBP: ffff88007ae41a98 R08: 0000000000000000 R09: 0000000000000001
[  608.368010] R10: ffffea0001f22e40 R11: ffffffff814151d5 R12: 0000000000000004
[  608.368010] R13: ffff880036470000 R14: 0000000000000004 R15: ffff880036472400
[  608.368010] FS:  00007ff7a5268700(0000) GS:ffff88007fd00000(0000) knlGS:0000000000000000
[  608.368010] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[  608.368010] CR2: 0000000000000028 CR3: 000000007a0fd000 CR4: 00000000000006e0
[  608.368010] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  608.368010] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[  608.368010] Process stress_test_tty (pid: 1918, threadinfo ffff88007ae40000, task ffff88003688dc40)
[  608.368010] Stack:
[  608.368010]  ffff880036472400 0000000000000001 ffff88007ae41aa8 ffffffff81417e98
[  608.368010]  ffff88007ae41ac8 ffffffff8140c42b ffff88007ac73100 ffff88007ac73100
[  608.368010]  ffff88007ae41b98 ffffffff8140ead5 ffff88007ae41b38 ffff88007ca40e40
[  608.368010] Call Trace:
[  608.368010]  [<ffffffff81417e98>] pty_unix98_shutdown+0x18/0x20
[  608.368010]  [<ffffffff8140c42b>] release_tty+0x3b/0xe0
[  608.368010]  [<ffffffff8140ead5>] __tty_release+0x575/0x5d0
[  608.368010]  [<ffffffff816d2c63>] ? _raw_spin_lock+0x23/0x30
[  608.368010]  [<ffffffff816d28ea>] ? _raw_spin_unlock+0x1a/0x40
[  608.368010]  [<ffffffff816d03e8>] ? __mutex_unlock_slowpath+0x48/0x60
[  608.368010]  [<ffffffff8140ef79>] tty_open+0x449/0x5f0
[  608.368010]  [<ffffffff8119394b>] chrdev_open+0x9b/0x1c0
[  608.368010]  [<ffffffff8118d643>] do_dentry_open+0x203/0x290
[  608.368010]  [<ffffffff811938b0>] ? cdev_put+0x30/0x30
[  608.368010]  [<ffffffff8118d705>] finish_open+0x35/0x50
[  608.368010]  [<ffffffff8119dcce>] do_last+0x6fe/0xe90
[  608.368010]  [<ffffffff8119a7af>] ? link_path_walk+0x7f/0x880
[  608.368010]  [<ffffffff8119e51c>] path_openat+0xbc/0x4e0
[  608.368010]  [<ffffffff8119ec11>] do_filp_open+0x41/0xa0
[  608.368010]  [<ffffffff816d28ea>] ? _raw_spin_unlock+0x1a/0x40
[  608.368010]  [<ffffffff811abe39>] ? __alloc_fd+0xe9/0x140
[  608.368010]  [<ffffffff8118ea44>] do_sys_open+0xf4/0x1e0
[  608.368010]  [<ffffffff816d2c63>] ? _raw_spin_lock+0x23/0x30
[  608.368010]  [<ffffffff8118eb51>] sys_open+0x21/0x30
[  608.368010]  [<ffffffff816da719>] system_call_fastpath+0x16/0x1b
[  608.368010] Code: ec 48 83 c4 10 5b 41 5c 5d c3 66 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 48 89 e5 48 83 ec 10 4c 89 65 f8 41 89 f4 48 89 5d f0 <48> 8b 47 28 48 81 78 58 d1 1c 00 00 74 0b 48 8b 05 4b 66 cf 00
[  608.368010] RIP  [<ffffffff812078d8>] devpts_kill_index+0x18/0x70
[  608.368010]  RSP <ffff88007ae41a88>
[  608.368010] CR2: 0000000000000028
[  608.394153] ---[ end trace afe83b0fb5fbda93 ]---

Reported-by: Ilya Zykov <ilya@ilyx.ru>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/pty.c

@@ -55,7 +55,8 @@ static void pty_close(struct tty_struct *tty, struct file *filp)
 #ifdef CONFIG_UNIX98_PTYS
 		if (tty->driver == ptm_driver) {
 			mutex_lock(&devpts_mutex);
-			devpts_pty_kill(tty->link->driver_data);
+			if (tty->link->driver_data)
+				devpts_pty_kill(tty->link->driver_data);
 			mutex_unlock(&devpts_mutex);
 		}
 #endif
@@ -703,6 +704,7 @@ static int ptmx_open(struct inode *inode, struct file *filp)
 	mutex_unlock(&tty_mutex);
 
 	set_bit(TTY_PTY_LOCK, &tty->flags); /* LOCK THE SLAVE */
+	tty->driver_data = inode;
 
 	tty_add_file(tty, filp);
 
@@ -713,14 +715,13 @@ static int ptmx_open(struct inode *inode, struct file *filp)
 		retval = PTR_ERR(slave_inode);
 		goto err_release;
 	}
+	tty->link->driver_data = slave_inode;
 
 	retval = ptm_driver->ops->open(tty, filp);
 	if (retval)
 		goto err_release;
 
 	tty_unlock(tty);
-	tty->driver_data = inode;
-	tty->link->driver_data = slave_inode;
 	return 0;
 err_release:
 	tty_unlock(tty);