Re: use-after-free in tty_check_change

From: Dmitry Vyukov
Date: Thu Nov 26 2015 - 09:00:59 EST

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On Thu, Nov 26, 2015 at 2:29 PM, Peter Hurley <peter@xxxxxxxxxxxxxxxxxx> wrote:
> On 11/26/2015 08:09 AM, Dmitry Vyukov wrote:
>> On Thu, Nov 26, 2015 at 2:00 PM, Peter Hurley <peter@xxxxxxxxxxxxxxxxxx> wrote:
>>> Hi Dmitry,
>>>
>>> On 11/26/2015 05:31 AM, Dmitry Vyukov wrote:
>>>> Hello,
>>>>
>>>> The following program causes a use-after-free in tty_check_change:
>>>>
>>>> // autogenerated by syzkaller (http://github.com/google/syzkaller)
>>>> #include <sys/types.h>
>>>> #include <sys/stat.h>
>>>> #include <fcntl.h>
>>>> #include <sys/ioctl.h>
>>>>
>>>> void *thr(void *arg)
>>>> {
>>>> int x = 0;
>>>> ioctl((int)(long)arg, TIOCGETD, &x);
>>>> return 0;
>>>> }
>>>>
>>>> void tty()
>>>> {
>>>> int fd = open("/dev/ptmx", O_RDONLY|O_SYNC);
>>>> pthread_t th;
>>>> pthread_create(&th, 0, thr, (void*)(long)fd);
>>>> int x = 16;
>>>> ioctl(fd, TIOCSETD, &x);
>>>> pthread_join(th, 0);
>>>> }
>>>>
>>>> int main()
>>>> {
>>>> int i;
>>>>
>>>> for (i = 0; i < 10; i++) {
>>>> if (fork() == 0) {
>>>> tty();
>>>> return 0;
>>>> }
>>>> }
>>>> return 0;
>>>> }
>>>>
>>>>
>>>> ==================================================================
>>>> BUG: KASAN: use-after-free in tty_ioctl+0x1f06/0x2140 at addr ffff880061aa0968
>>>> Read of size 8 by task a.out/6241
>>>> =============================================================================
>>>> BUG kmalloc-16 (Not tainted): kasan: bad access detected
>>>> -----------------------------------------------------------------------------
>>>
>>> Thanks for the report. I think I have the patch that fixes this in
>>> my out-queue as part of a larger patchset.
>>>
>>> However, the stack backtrace below and the reported eip don't correspond
>>> to the what I think the problem is:
>>>
>>>
>>>> BUG: KASAN: use-after-free in tty_ioctl+0x1f06/0x2140 at addr ffff880061aa0968
>>> ^^^^^^^^^^^^^^
>>> this offset is off the end of compilation unit for me with gcc 4.8.4
>>>
>>> Could you generate a mixed listing file of drivers/tty/tty_io.c and attach
>>> it please?
>>
>>
>> The source is plain 6ffeba9607343f15303a399bc402a538800d89d9, but I
>> use CONFIG_KASAN=y, CONFIG_KASAN_INLINE=y and gcc version 6.0.0
>> 20151014. KASAN does affect generated code significantly.
>> Line numbers in the report should be correct.
>
> current->signal? I doubt it. Also note the stack trace pulls the wrong
> symbol: should be __tty_check_change on line 399, not tty_check_change().
>
>>>> Call Trace:
>>>> [<ffffffff81631fde>] __asan_report_load8_noabort+0x3e/0x40
>>>> mm/kasan/report.c:280
>>>> [< inline >] tty_check_change drivers/tty/tty_io.c:399
> ^^^^^^^^^^^^
> |
> +------------------------------------------+
> | |
> $ git blame -L393,409 -s 6ffeba960734 -- drivers/tty/tty_io.c
> 2812d9e9 drivers/tty/tty_io.c 393) int __tty_check_change(struct tty_struct *tty, int sig)
> ^1da177e drivers/char/tty_io.c 394) {
> 47f86834 drivers/char/tty_io.c 395) unsigned long flags;
> 2812d9e9 drivers/tty/tty_io.c 396) struct pid *pgrp, *tty_pgrp;
> 47f86834 drivers/char/tty_io.c 397) int ret = 0;
> 47f86834 drivers/char/tty_io.c 398)
> ^1da177e drivers/char/tty_io.c 399) if (current->signal->tty != tty) <<<==== ???
> ^1da177e drivers/char/tty_io.c 400) return 0;
> 47f86834 drivers/char/tty_io.c 401)
> 6719693c drivers/tty/tty_io.c 402) rcu_read_lock();
> 6719693c drivers/tty/tty_io.c 403) pgrp = task_pgrp(current);
> 6719693c drivers/tty/tty_io.c 404)
> 47f86834 drivers/char/tty_io.c 405) spin_lock_irqsave(&tty->ctrl_lock, flags);
> 2812d9e9 drivers/tty/tty_io.c 406) tty_pgrp = tty->pgrp;
> 9ffee4cb drivers/char/tty_io.c 407) spin_unlock_irqrestore(&tty->ctrl_lock, flags);
> 6719693c drivers/tty/tty_io.c 408)
> 2812d9e9 drivers/tty/tty_io.c 409) if (tty_pgrp && pgrp != tty->pgrp) {
>
>
> The disassembly would really help. Feel free to send it to me off-list.
>
> Regards,
> Peter Hurley
>
>>>> Disabling lock debugging due to kernel taint
>>>> INFO: Allocated in tty_ldisc_get.part.3+0x66/0x140 age=6 cpu=3 pid=6230
>>>> [< none >] kmem_cache_alloc_trace+0x1cf/0x220 mm/slub.c:2589
>>>> [< none >] tty_ldisc_get.part.3+0x66/0x140 drivers/tty/tty_ldisc.c:172
>>>> [< none >] tty_set_ldisc+0x83d/0xa70 drivers/tty/tty_ldisc.c:574
>>>> [< none >] tty_ioctl+0xb2a/0x2140 drivers/tty/tty_io.c:2865
>>>> [< inline >] spin_unlock include/linux/spinlock.h:347
>>>> [< inline >] ioctl_fionbio fs/ioctl.c:492
>>>> [< none >] do_vfs_ioctl+0x681/0xe40 fs/ioctl.c:572
>>>> [< none >] SyS_ioctl+0x8f/0xc0 fs/readdir.c:25
>>>> [< none >] entry_SYSCALL_64_fastpath+0x16/0x7a
>>>> arch/x86/entry/entry_64.S:185
>>>>
>>>> INFO: Freed in tty_set_ldisc+0x4c2/0xa70 age=12 cpu=3 pid=6230
>>>> [< none >] kfree+0x199/0x1b0 mm/slub.c:3632
>>>> [< inline >] tty_ldisc_restore drivers/tty/tty_ldisc.c:493
>>>> [< none >] tty_set_ldisc+0x4c2/0xa70 drivers/tty/tty_ldisc.c:571
>>>> [< none >] tty_ioctl+0xb2a/0x2140 drivers/tty/tty_io.c:2865
>>>> [< inline >] spin_unlock include/linux/spinlock.h:347
>>>> [< inline >] ioctl_fionbio fs/ioctl.c:492
>>>> [< none >] do_vfs_ioctl+0x681/0xe40 fs/ioctl.c:572
>>>> [< none >] SyS_ioctl+0x8f/0xc0 fs/readdir.c:25
>>>> [< none >] entry_SYSCALL_64_fastpath+0x16/0x7a
>>>> arch/x86/entry/entry_64.S:185
>>>>
>>>> INFO: Slab 0xffffea000186a800 objects=23 used=19 fp=0xffff880061aa12d0
>>>> flags=0x5fffc0000004080
>>>> INFO: Object 0xffff880061aa0968 @offset=2408 fp=0xffff880061aa0810
>>>> CPU: 2 PID: 6241 Comm: a.out Tainted: G B 4.4.0-rc1+ #117
>>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>>>> 00000000ffffffff ffff88006db0fab8 ffffffff827450f6 ffff88003e807980
>>>> ffff880061aa0968 ffff880061aa0000 ffff88006db0fae8 ffffffff81629404
>>>> ffff88003e807980 ffffea000186a800 ffff880061aa0968 000000000000001b
>>>>
>>>> Call Trace:
>>>> [<ffffffff81631fde>] __asan_report_load8_noabort+0x3e/0x40
>>>> mm/kasan/report.c:280
>>>> [< inline >] tty_check_change drivers/tty/tty_io.c:399
>>>> [<ffffffff82a7b0a6>] tty_ioctl+0x1f06/0x2140 drivers/tty/tty_io.c:2831
>>>> [< inline >] spin_unlock include/linux/spinlock.h:347
>>>> [< inline >] ioctl_fionbio fs/ioctl.c:492
>>>> [<ffffffff816aea91>] do_vfs_ioctl+0x681/0xe40 fs/ioctl.c:572
>>>> [<ffffffff816af2df>] SyS_ioctl+0x8f/0xc0 fs/readdir.c:25
>>>> [<ffffffff85415cf6>] entry_SYSCALL_64_fastpath+0x16/0x7a
>>>> arch/x86/entry/entry_64.S:185
>>>> ==================================================================
>>>>
>>>>
>>>> On commit 6ffeba9607343f15303a399bc402a538800d89d9 (Nov 24).

Uh, sorry, I used a wrong vmlinux for postprocessing.
Here is a proper report.
drivers/tty/tty_io.c:2881 is:

case TIOCGETD:
return put_user(tty->ldisc->ops->num, (int __user *)p);

BUG: KASAN: use-after-free in tty_ioctl+0x1d1c/0x1fd0 at addr ffff8800640bc810
Read of size 8 by task a.out/23957
=============================================================================
BUG kmalloc-16 (Tainted: G B ): kasan: bad access detected
-----------------------------------------------------------------------------

INFO: Allocated in tty_ldisc_get.part.3+0x61/0x130 age=0 cpu=3 pid=23947
[< none >] ___slab_alloc+0x489/0x4e0 mm/slub.c:2438
[< none >] __slab_alloc+0x4c/0x90 mm/slub.c:2467
[< inline >] slab_alloc_node mm/slub.c:2530
[< inline >] slab_alloc mm/slub.c:2572
[< none >] kmem_cache_alloc_trace+0x1c6/0x210 mm/slub.c:2589
[< inline >] kmalloc include/linux/slab.h:458
[< none >] tty_ldisc_get.part.3+0x61/0x130 drivers/tty/tty_ldisc.c:171
[< inline >] tty_ldisc_get drivers/tty/tty_ldisc.c:190
[< inline >] tty_ldisc_restore drivers/tty/tty_ldisc.c:490
[< none >] tty_set_ldisc+0x74c/0x940 drivers/tty/tty_ldisc.c:571
[< inline >] tiocsetd drivers/tty/tty_io.c:2650
[< none >] tty_ioctl+0xace/0x1fd0 drivers/tty/tty_io.c:2883
[< inline >] vfs_ioctl fs/ioctl.c:43
[< none >] do_vfs_ioctl+0x57c/0xe60 fs/ioctl.c:607
[< inline >] SYSC_ioctl fs/ioctl.c:622
[< none >] SyS_ioctl+0x74/0x80 fs/ioctl.c:613
[< none >] entry_SYSCALL_64_fastpath+0x16/0x7a
arch/x86/entry/entry_64.S:185

INFO: Freed in tty_set_ldisc+0x423/0x940 age=0 cpu=3 pid=23947
[< none >] __slab_free+0x206/0x360 mm/slub.c:2648 (discriminator 1)
[< inline >] slab_free mm/slub.c:2803
[< none >] kfree+0x1a2/0x1c0 mm/slub.c:3632
[< inline >] tty_ldisc_put drivers/tty/tty_ldisc.c:194
[< none >] tty_set_ldisc+0x423/0x940 drivers/tty/tty_ldisc.c:570
[< inline >] tiocsetd drivers/tty/tty_io.c:2650
[< none >] tty_ioctl+0xace/0x1fd0 drivers/tty/tty_io.c:2883
[< inline >] vfs_ioctl fs/ioctl.c:43
[< none >] do_vfs_ioctl+0x57c/0xe60 fs/ioctl.c:607
[< inline >] SYSC_ioctl fs/ioctl.c:622
[< none >] SyS_ioctl+0x74/0x80 fs/ioctl.c:613
[< none >] entry_SYSCALL_64_fastpath+0x16/0x7a
arch/x86/entry/entry_64.S:185
INFO: Slab 0xffffea0001902f00 objects=23 used=3 fp=0xffff8800640bc000
flags=0x5fffc0000004080
INFO: Object 0xffff8800640bc810 @offset=2064 fp=0xffff8800640bc000

Bytes b4 ffff8800640bc800: 15 1d 3b 00 01 00 00 00 5a 5a 5a 5a 5a 5a
5a 5a ..;.....ZZZZZZZZ
Object ffff8800640bc810: a0 9b 3d 86 ff ff ff ff 60 ef 16 6d 00 88 ff
ff ..=.....`..m....
Redzone ffff8800640bc820: cc cc cc cc cc cc cc cc
........
Padding ffff8800640bc960: 5a 5a 5a 5a 5a 5a 5a 5a
ZZZZZZZZ
CPU: 0 PID: 23957 Comm: a.out Tainted: G B 4.4.0-rc2+ #51
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
ffff8800640bc000 ffff88006127fab8 ffffffff826c8be0 ffff88003e807980
ffff88006127fae8 ffffffff815f1604 ffff88003e807980 ffffea0001902f00
ffff8800640bc810 0000000000005424 ffff88006127fb10 ffffffff815f775f
Call Trace:
[< inline >] __dump_stack lib/dump_stack.c:15
[<ffffffff826c8be0>] dump_stack+0x44/0x64 lib/dump_stack.c:50
[<ffffffff815f1604>] print_trailer+0xf4/0x150 mm/slub.c:652
[<ffffffff815f775f>] object_err+0x2f/0x40 mm/slub.c:659
[< inline >] print_address_description mm/kasan/report.c:138
[<ffffffff815f9ee0>] kasan_report_error+0x210/0x520 mm/kasan/report.c:236
[< inline >] kasan_report mm/kasan/report.c:259
[<ffffffff815fa2ee>] __asan_report_load8_noabort+0x3e/0x40
mm/kasan/report.c:280
[<ffffffff829db6ec>] tty_ioctl+0x1d1c/0x1fd0 drivers/tty/tty_io.c:2881
[< inline >] vfs_ioctl fs/ioctl.c:43
[<ffffffff816708ac>] do_vfs_ioctl+0x57c/0xe60 fs/ioctl.c:607
[< inline >] SYSC_ioctl fs/ioctl.c:622
[<ffffffff81671204>] SyS_ioctl+0x74/0x80 fs/ioctl.c:613
[<ffffffff852a7876>] entry_SYSCALL_64_fastpath+0x16/0x7a
arch/x86/entry/entry_64.S:185
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Next message: Radim KrcmÃr: "Re: [PATCH] KVM: x86: Add lowest-priority support for vt-d posted-interrupts"
Previous message: MyungJoo Ham: "Re: [RFC PATCH 01/15] PM / devfreq: exynos: Add generic exynos bus frequency driver"
In reply to: Peter Hurley: "Re: use-after-free in tty_check_change"
Next in thread: Peter Hurley: "Re: use-after-free in tty_check_change"
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