Re: tty: panic in tty_ldisc_restore

[Greg Kroah-Hartman]

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?

thanks,

greg k-h