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)); if (!ldata) goto err; On commit 510948533b059f4f5033464f9f4a0c32d4ab0c08 of mmotm tree.