Messages in this thread | | | From | Dmitry Vyukov <> | Date | Tue, 7 Feb 2017 11:51:24 +0100 | Subject | Re: tty: panic in tty_ldisc_restore |
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On Tue, Feb 7, 2017 at 11:43 AM, Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote: > On Tue, Feb 07, 2017 at 11:24:13AM +0100, Dmitry Vyukov wrote: >> On Thu, Feb 2, 2017 at 7:23 PM, Greg Kroah-Hartman >> <gregkh@linuxfoundation.org> wrote: >> > On Thu, Feb 02, 2017 at 07:03:41PM +0100, Dmitry Vyukov wrote: >> >> On Thu, Feb 2, 2017 at 6:55 PM, Greg Kroah-Hartman >> >> <gregkh@linuxfoundation.org> wrote: >> >> > On Thu, Feb 02, 2017 at 06:48:48PM +0100, Dmitry Vyukov wrote: >> >> >> Hello, >> >> >> >> >> >> Syzkaller fuzzer started crashing kernel with the following panics: >> >> >> >> >> >> Kernel panic - not syncing: Couldn't open N_TTY ldisc for ircomm0 --- error -12. >> >> >> CPU: 0 PID: 5637 Comm: syz-executor3 Not tainted 4.9.0 #6 >> >> >> Hardware name: Google Google Compute Engine/Google Compute Engine, >> >> >> BIOS Google 01/01/2011 >> >> >> ffff8801d4ba7a18 ffffffff8234d0df ffffffff00000000 1ffff1003a974ed6 >> >> >> ffffed003a974ece 0000000041b58ab3 ffffffff84b38180 ffffffff8234cdf1 >> >> >> 0000000000000000 0000000000000000 ffff8801d4ba76a8 00000000dabb4fad >> >> >> Call Trace: >> >> >> [<ffffffff8234d0df>] __dump_stack lib/dump_stack.c:15 [inline] >> >> >> [<ffffffff8234d0df>] dump_stack+0x2ee/0x3ef lib/dump_stack.c:51 >> >> >> [<ffffffff818280d4>] panic+0x1fb/0x412 kernel/panic.c:179 >> >> >> [<ffffffff826bb0d4>] tty_ldisc_restore drivers/tty/tty_ldisc.c:520 [inline] >> >> >> [<ffffffff826bb0d4>] tty_set_ldisc+0x704/0x8b0 drivers/tty/tty_ldisc.c:579 >> >> >> [<ffffffff826a3a93>] tiocsetd drivers/tty/tty_io.c:2667 [inline] >> >> >> [<ffffffff826a3a93>] tty_ioctl+0xc63/0x2370 drivers/tty/tty_io.c:2924 >> >> >> [<ffffffff81a7a22f>] vfs_ioctl fs/ioctl.c:43 [inline] >> >> >> [<ffffffff81a7a22f>] do_vfs_ioctl+0x1bf/0x1630 fs/ioctl.c:679 >> >> >> [<ffffffff81a7b72f>] SYSC_ioctl fs/ioctl.c:694 [inline] >> >> >> [<ffffffff81a7b72f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685 >> >> >> [<ffffffff84377941>] entry_SYSCALL_64_fastpath+0x1f/0xc2 >> >> >> >> >> >> Kernel panic - not syncing: Couldn't open N_TTY ldisc for ptm2 --- error -12. >> >> >> CPU: 0 PID: 7844 Comm: syz-executor0 Not tainted 4.9.0 #6 >> >> >> Hardware name: Google Google Compute Engine/Google Compute Engine, >> >> >> BIOS Google 01/01/2011 >> >> >> ffff8801c3307a18 ffffffff8234d0df ffffffff00000000 1ffff10038660ed6 >> >> >> ffffed0038660ece 0000000041b58ab3 ffffffff84b38180 ffffffff8234cdf1 >> >> >> 0000000000000000 0000000000000000 ffff8801c33076a8 00000000dabb4fad >> >> >> Call Trace: >> >> >> [<ffffffff8234d0df>] __dump_stack lib/dump_stack.c:15 [inline] >> >> >> [<ffffffff8234d0df>] dump_stack+0x2ee/0x3ef lib/dump_stack.c:51 >> >> >> [<ffffffff818280d4>] panic+0x1fb/0x412 kernel/panic.c:179 >> >> >> [<ffffffff826bb0d4>] tty_ldisc_restore drivers/tty/tty_ldisc.c:520 [inline] >> >> >> [<ffffffff826bb0d4>] tty_set_ldisc+0x704/0x8b0 drivers/tty/tty_ldisc.c:579 >> >> >> [<ffffffff826a3a93>] tiocsetd drivers/tty/tty_io.c:2667 [inline] >> >> >> [<ffffffff826a3a93>] tty_ioctl+0xc63/0x2370 drivers/tty/tty_io.c:2924 >> >> >> [<ffffffff81a7a22f>] vfs_ioctl fs/ioctl.c:43 [inline] >> >> >> [<ffffffff81a7a22f>] do_vfs_ioctl+0x1bf/0x1630 fs/ioctl.c:679 >> >> >> [<ffffffff81a7b72f>] SYSC_ioctl fs/ioctl.c:694 [inline] >> >> >> [<ffffffff81a7b72f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685 >> >> >> [<ffffffff84377941>] entry_SYSCALL_64_fastpath+0x1f/0xc2 >> >> >> >> >> >> >> >> >> In all cases there is a vmalloc failure right before that: >> >> >> >> >> >> syz-executor4: vmalloc: allocation failure, allocated 0 of 16384 >> >> >> bytes, mode:0x14000c2(GFP_KERNEL|__GFP_HIGHMEM), nodemask=(null) >> >> >> syz-executor4 cpuset=/ mems_allowed=0 >> >> >> CPU: 1 PID: 4852 Comm: syz-executor4 Not tainted 4.9.0 #6 >> >> >> Hardware name: Google Google Compute Engine/Google Compute Engine, >> >> >> BIOS Google 01/01/2011 >> >> >> ffff8801c41df898 ffffffff8234d0df ffffffff00000001 1ffff1003883bea6 >> >> >> ffffed003883be9e 0000000041b58ab3 ffffffff84b38180 ffffffff8234cdf1 >> >> >> 0000000000000282 ffffffff84fd53c0 ffff8801dae65b38 ffff8801c41df4d0 >> >> >> Call Trace: >> >> >> [< inline >] __dump_stack lib/dump_stack.c:15 >> >> >> [<ffffffff8234d0df>] dump_stack+0x2ee/0x3ef lib/dump_stack.c:51 >> >> >> [<ffffffff8186530f>] warn_alloc+0x21f/0x360 >> >> >> [<ffffffff819792c9>] __vmalloc_node_range+0x4e9/0x770 >> >> >> [< inline >] __vmalloc_node mm/vmalloc.c:1749 >> >> >> [< inline >] __vmalloc_node_flags mm/vmalloc.c:1763 >> >> >> [<ffffffff8197961b>] vmalloc+0x5b/0x70 mm/vmalloc.c:1778 >> >> >> [<ffffffff826ad77b>] n_tty_open+0x1b/0x470 drivers/tty/n_tty.c:1883 >> >> >> [<ffffffff826ba973>] tty_ldisc_open.isra.3+0x73/0xd0 >> >> >> drivers/tty/tty_ldisc.c:463 >> >> >> [< inline >] tty_ldisc_restore drivers/tty/tty_ldisc.c:510 >> >> >> [<ffffffff826bafb4>] tty_set_ldisc+0x5e4/0x8b0 drivers/tty/tty_ldisc.c:579 >> >> >> [< inline >] tiocsetd drivers/tty/tty_io.c:2667 >> >> >> [<ffffffff826a3a93>] tty_ioctl+0xc63/0x2370 drivers/tty/tty_io.c:2924 >> >> >> [<ffffffff81a7a22f>] do_vfs_ioctl+0x1bf/0x1630 >> >> >> [< inline >] SYSC_ioctl fs/ioctl.c:698 >> >> >> [<ffffffff81a7b72f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:689 >> >> >> [<ffffffff84377941>] entry_SYSCALL_64_fastpath+0x1f/0xc2 >> >> >> arch/x86/entry/entry_64.S:204 >> >> >> >> >> >> >> >> >> I've found that it's even documented in the source code, but it does >> >> >> not look like a good failure mode for allocation failure: >> >> >> >> >> >> static int n_tty_open(struct tty_struct *tty) >> >> >> { >> >> >> struct n_tty_data *ldata; >> >> >> >> >> >> /* Currently a malloc failure here can panic */ >> >> >> ldata = vmalloc(sizeof(*ldata)); >> >> > >> >> > How are you running out of vmalloc() memory? >> >> >> >> >> >> I don't know exactly. But it does not seem to represent a problem for >> >> the fuzzer. >> >> Is it meant to be very hard to do? >> > >> > Yes, do you know of any normal way to cause it to fail? >> >> >> I don't. But I means approximately nothing. >> Do you mean that it is not possible to trigger? >> Doesn't simply creating lots of kernel resources (files, sockets, >> pipe) will do the trick? Or just paging in lots of memory? Even if the >> process itself will be chosen as OOM kill target, it will still take >> the machine down with itself due to the panic while returning from the >> syscall, no? > > I'm not saying that it's impossible, just an "almost" impossible thing > to hit. Obviously you have hit it, so it can happen :) > > But, how to fix it? I really don't know. Unwinding a failure at this > point in time is very tough, as that comment shows. Any suggestions of > how it could be resolved are greatly appreciated.
Is it possible to not shutdown the old discipline tty_set_ldisc before we prepare everything for the new one:
/* Shutdown the old discipline. */ tty_ldisc_close(tty, old_ldisc);
Currently it does:
close(old) if (open(new)) open(old) // assume never fails
it looks inherently problematic. Couldn't we do:
if (open(new)) return -ESOMETHING close(old)
?
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