Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752222AbbKZNAy (ORCPT ); Thu, 26 Nov 2015 08:00:54 -0500 Received: from mail-io0-f177.google.com ([209.85.223.177]:36504 "EHLO mail-io0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751045AbbKZNAv (ORCPT ); Thu, 26 Nov 2015 08:00:51 -0500 Subject: Re: use-after-free in tty_check_change To: Dmitry Vyukov References: Cc: Greg Kroah-Hartman , Jiri Slaby , LKML , syzkaller , Kostya Serebryany , Alexander Potapenko , Sasha Levin , Eric Dumazet From: Peter Hurley Message-ID: <56570280.5030505@hurleysoftware.com> Date: Thu, 26 Nov 2015 08:00:48 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4781 Lines: 124 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? 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). -- 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/