Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752709AbbKZOA5 (ORCPT ); Thu, 26 Nov 2015 09:00:57 -0500 Received: from mail-wm0-f51.google.com ([74.125.82.51]:37001 "EHLO mail-wm0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752636AbbKZOAv (ORCPT ); Thu, 26 Nov 2015 09:00:51 -0500 MIME-Version: 1.0 In-Reply-To: <5657091D.5010500@hurleysoftware.com> References: <56570280.5030505@hurleysoftware.com> <5657091D.5010500@hurleysoftware.com> From: Dmitry Vyukov Date: Thu, 26 Nov 2015 15:00:29 +0100 Message-ID: Subject: Re: use-after-free in tty_check_change To: Peter Hurley Cc: Greg Kroah-Hartman , Jiri Slaby , LKML , syzkaller , Kostya Serebryany , Alexander Potapenko , Sasha Levin , Eric Dumazet Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 11581 Lines: 253 On Thu, Nov 26, 2015 at 2:29 PM, Peter Hurley wrote: > On 11/26/2015 08:09 AM, Dmitry Vyukov wrote: >> On Thu, Nov 26, 2015 at 2:00 PM, Peter Hurley 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 >>>> #include >>>> #include >>>> #include >>>> >>>> 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: >>>> [] __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: >>>> [] __asan_report_load8_noabort+0x3e/0x40 >>>> mm/kasan/report.c:280 >>>> [< inline >] tty_check_change drivers/tty/tty_io.c:399 >>>> [] 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 >>>> [] do_vfs_ioctl+0x681/0xe40 fs/ioctl.c:572 >>>> [] SyS_ioctl+0x8f/0xc0 fs/readdir.c:25 >>>> [] 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 [] dump_stack+0x44/0x64 lib/dump_stack.c:50 [] print_trailer+0xf4/0x150 mm/slub.c:652 [] object_err+0x2f/0x40 mm/slub.c:659 [< inline >] print_address_description mm/kasan/report.c:138 [] kasan_report_error+0x210/0x520 mm/kasan/report.c:236 [< inline >] kasan_report mm/kasan/report.c:259 [] __asan_report_load8_noabort+0x3e/0x40 mm/kasan/report.c:280 [] tty_ioctl+0x1d1c/0x1fd0 drivers/tty/tty_io.c:2881 [< inline >] vfs_ioctl fs/ioctl.c:43 [] do_vfs_ioctl+0x57c/0xe60 fs/ioctl.c:607 [< inline >] SYSC_ioctl fs/ioctl.c:622 [] SyS_ioctl+0x74/0x80 fs/ioctl.c:613 [] entry_SYSCALL_64_fastpath+0x16/0x7a arch/x86/entry/entry_64.S:185 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/