Hi Dmitry, On 11/26/2015 08:34 AM, Dmitry Vyukov wrote: > Hello, > > I've hit the following report once after booting a VM and then scp a > file into it. It is not reproducible. But maybe the stacks will give > you some hint as to how it could happen: > > > ================================================================== > BUG: KASAN: use-after-free in n_tty_read+0x1d53/0x1e60 at addr > ffff880061ec3ae0 > Read of size 8 by task sshd/5796 > ============================================================================= > BUG kmalloc-16 (Not tainted): kasan: bad access detected > -----------------------------------------------------------------------------
Thanks for the report. I have this fix in my out-queue, attached below for reference (which I'll now mark for -stable). Regards, Peter Hurley > Disabling lock debugging due to kernel taint > INFO: Allocated in tty_ldisc_get.part.3+0x61/0x130 age=11 cpu=3 pid=5796 > [< 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:801 > [< none >] tty_ldisc_init+0x13/0x70 drivers/tty/tty_ldisc.c:802 > [< none >] alloc_tty_struct+0x103/0x810 drivers/tty/tty_io.c:3115 > [< none >] pty_common_install+0x1a2/0x940 drivers/tty/pty.c:399 > [< none >] pty_unix98_install+0xb/0x10 drivers/tty/pty.c:674 > [< inline >] tty_driver_install_tty drivers/tty/tty_io.c:1430 > [< none >] tty_init_dev+0xdb/0x3e0 drivers/tty/tty_io.c:1529 > [< none >] ptmx_open+0xbc/0x2c0 drivers/tty/pty.c:762 > [< none >] chrdev_open+0x1ef/0x570 fs/char_dev.c:388 > [< none >] do_dentry_open+0x5d2/0xab0 fs/open.c:736 > [< none >] vfs_open+0x166/0x1e0 fs/open.c:853 > [< inline >] do_last fs/namei.c:3192 > [< none >] path_openat+0xa5c/0x5e00 fs/namei.c:3324 > [< none >] do_filp_open+0x170/0x230 fs/namei.c:3359 > [< none >] do_sys_open+0x180/0x360 fs/open.c:1025 > > INFO: Freed in tty_ldisc_reinit+0xc8/0x1b0 age=7 cpu=0 pid=5798 > [< 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_ldisc_reinit+0xc8/0x1b0 drivers/tty/tty_ldisc.c:635 > [< none >] tty_ldisc_hangup+0x1fa/0x5f0 drivers/tty/tty_ldisc.c:708 > [< none >] __tty_hangup+0x423/0xad0 drivers/tty/tty_io.c:729 > [< inline >] tty_vhangup drivers/tty/tty_io.c:802 > [< none >] tty_vhangup_self+0x1c/0x40 drivers/tty/tty_io.c:820 > [< none >] sys_vhangup+0x1e/0x30 fs/open.c:1121 > [< none >] entry_SYSCALL_64_fastpath+0x16/0x7a > arch/x86/entry/entry_64.S:185 > INFO: Slab 0xffffea000187b080 objects=23 used=16 fp=0xffff880061ec3ae0 > flags=0x5fffc0000004080 > INFO: Object 0xffff880061ec3ae0 @offset=6880 fp=0xffff880061ec3580 > > Bytes b4 ffff880061ec3ad0: f1 c1 fb ff 00 00 00 00 5a 5a 5a 5a 5a 5a > 5a 5a ........ZZZZZZZZ > Object ffff880061ec3ae0: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b > a5 kkkkkkkkkkkkkkk. > Redzone ffff880061ec3af0: bb bb bb bb bb bb bb bb > ........ > Padding ffff880061ec3c30: 5a 5a 5a 5a 5a 5a 5a 5a > ZZZZZZZZ > CPU: 3 PID: 5796 Comm: sshd Tainted: G B 4.4.0-rc2+ #51 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 > ffff880061ec2000 ffff88006a377928 ffffffff826c8be0 ffff88003e807980 > ffff88006a377958 ffffffff815f1604 ffff88003e807980 ffffea000187b080 > ffff880061ec3ae0 ffff8800620c4670 ffff88006a377980 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 > [< inline >] n_tty_check_unthrottle drivers/tty/n_tty.c:262 > [<ffffffff829e73b3>] n_tty_read+0x1d53/0x1e60 drivers/tty/n_tty.c:2302 > [<ffffffff829d8596>] tty_read+0x146/0x230 drivers/tty/tty_io.c:1071 > [<ffffffff81633bcb>] __vfs_read+0xdb/0x490 fs/read_write.c:432 > [<ffffffff81635edb>] vfs_read+0xdb/0x2d0 fs/read_write.c:454 > [< inline >] SYSC_read fs/read_write.c:569 > [<ffffffff81638c1c>] SyS_read+0x10c/0x220 fs/read_write.c:562 > [<ffffffff852a7876>] entry_SYSCALL_64_fastpath+0x16/0x7a > arch/x86/entry/entry_64.S:185 > ================================================================== > > > On commit 6ffeba9607343f15303a399bc402a538800d89d9. > --- >% --- Subject: [PATCH] n_tty: Fix unsafe reference to "other" ldisc Although n_tty_check_unthrottle() has a valid ldisc reference (since the tty core gets the ldisc ref in tty_read() before calling the line discipline read() method), it does not have a valid ldisc reference to the "other" pty of a pty pair. Since getting an ldisc reference for tty->link essentially open-codes tty_wakeup(), just replace with the equivalent tty_wakeup(). Signed-off-by: Peter Hurley <[email protected]> --- drivers/tty/n_tty.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c index 1dcd10b..58e009d 100644 --- a/drivers/tty/n_tty.c +++ b/drivers/tty/n_tty.c @@ -261,16 +261,13 @@ static void n_tty_check_throttle(struct tty_struct *tty) static void n_tty_check_unthrottle(struct tty_struct *tty) { - if (tty->driver->type == TTY_DRIVER_TYPE_PTY && - tty->link->ldisc->ops->write_wakeup == n_tty_write_wakeup) { + if (tty->driver->type == TTY_DRIVER_TYPE_PTY) { if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE) return; if (!tty->count) return; n_tty_kick_worker(tty); - n_tty_write_wakeup(tty->link); - if (waitqueue_active(&tty->link->write_wait)) - wake_up_interruptible_poll(&tty->link->write_wait, POLLOUT); + tty_wakeup(tty->link); return; } -- 2.6.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
