From b216df53848129c969a465bb9237fbc9b8fafaad Mon Sep 17 00:00:00 2001 From: Cyrill Gorcunov Date: Fri, 8 Aug 2014 00:26:15 +0400 Subject: [PATCH] tty: Fix potential use after free in release_one_tty In case if we're releasing the last tty reference the following call sequence is possible tty_driver_kref_put destruct_tty_driver kfree(driver); where @driver is used in next module_put call, which leads to | [ 285.964007] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 | [ 285.964007] Workqueue: events release_one_tty | [ 285.964007] task: ffff8800cc7ea5f0 ti: ffff8800cb800000 task.ti: ffff8800cb800000 | [ 285.964007] RIP: 0010:[] [] module_put+0x24/0xf4 | [ 285.964007] RSP: 0018:ffff8800cb801d48 EFLAGS: 00010213 | [ 285.964007] RAX: ffff8800cb801fd8 RBX: ffff8800ca3429d0 RCX: ffff8800cb1db400 | [ 285.964007] RDX: 0000000000000000 RSI: ffffffff817349c1 RDI: 0000000000000001 | [ 285.964007] RBP: ffff8800cb801d60 R08: ffff8800cd632b40 R09: 0000000000000000 | [ 285.964007] R10: 00000000ffffffff R11: ffff88011f40a000 R12: 6b6b6b6b6b6b6b6b | [ 285.964007] R13: ffff8800ca342520 R14: 0000000000000000 R15: ffff88011f5d8200 | [ 285.964007] FS: 0000000000000000(0000) GS:ffff88011f400000(0000) knlGS:0000000000000000 | [ 285.964007] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b | [ 285.964007] CR2: 00007faf5229d090 CR3: 0000000001c0b000 CR4: 00000000000006f0 | [ 285.964007] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 | [ 285.964007] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 | [ 285.964007] Stack: | [ 285.964007] ffff8800ca3429d0 ffff8800ca342a30 ffff8800ca342520 ffff8800cb801d88 | [ 285.964007] ffffffff8146554a ffff8800cc77cc78 ffff8800ca3429d0 ffff88011f5d3800 | [ 285.964007] ffff8800cb801e08 ffffffff810683c1 ffffffff810682ff 0000000000000046 | [ 285.964007] Call Trace: | [ 285.964007] [] release_one_tty+0x54/0xa3 | [ 285.964007] [] process_one_work+0x223/0x404 | [ 285.964007] [] ? process_one_work+0x161/0x404 | [ 285.964007] [] worker_thread+0x136/0x205 | [ 285.964007] [] ? rescuer_thread+0x26a/0x26a | [ 285.964007] [] kthread+0xa2/0xaa | [ 285.964007] [] ? trace_hardirqs_on_caller+0x16/0x1eb | [ 285.964007] [] ? __kthread_parkme+0x65/0x65 | [ 285.964007] [] ret_from_fork+0x7c/0xb0 | [ 285.964007] [] ? __kthread_parkme+0x65/0x65 | [ 285.964007] Code: 09 00 5b 41 5c 5d c3 0f 1f 44 00 00 55 48 85 ff 48 89 e5 41 55 41 54 49 89 fc 53 0f 84 d3 00 | 00 00 bf 01 00 00 00 e8 d0 a1 fc ff <49> 8b 84 24 50 02 00 00 65 48 ff 40 08 4c 8b 6d 08 0f 1f 44 00 so simply keep a local reference to the module owner and use it later. CC: Pavel Emelyanov CC: Jiri Slaby CC: Greg Kroah-Hartman Signed-off-by: Cyrill Gorcunov Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_io.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index 8fbad3410c75..d4eb2a8b7047 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -1544,13 +1544,14 @@ static void release_one_tty(struct work_struct *work) struct tty_struct *tty = container_of(work, struct tty_struct, hangup_work); struct tty_driver *driver = tty->driver; + struct module *owner = driver->owner; if (tty->ops->cleanup) tty->ops->cleanup(tty); tty->magic = 0; tty_driver_kref_put(driver); - module_put(driver->owner); + module_put(owner); spin_lock(&tty_files_lock); list_del_init(&tty->tty_files); -- 2.20.1