Kernel panic in tty_insert_flip_string() function.

Issue

• Kernel panic with the following call traces.

BUG: unable to handle kernel NULL pointer dereference at 0000000000000018
IP: [<ffffffff8131e38e>] tty_insert_flip_string+0x6e/0xd0
PGD 0 
Oops: 0000 [#1] SMP 
last sysfs file: /sys/devices/virtual/net/virbr0-nic/speed
CPU 0 
Modules linked in: nfsd exportfs nfs lockd fscache nfs_acl auth_rpcgss fuse ebtable_nat ebtables ipt_REJECT  
xt_CHECKSUM bridge stp llc autofs4 sunrpc ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 xt_state nf_conntrack 
ip6table_filter ip6_tables ipv6 vhost_net macvtap macvlan tun uinput microcode sg virtio_balloon snd_hda_intel
snd_hda_codec snd_hwdep snd_seq snd_seq_device snd_pcm snd_timer snd soundcore snd_page_alloc 8139too 
8139cp mii i2c_piix4 i2c_core ext4 mbcache jbd2 virtio_blk sd_mod crc_t10dif sr_mod cdrom virtio_pci virtio_ring
virtio pata_acpi ata_generic ata_piix dm_mirror dm_region_hash dm_log dm_mod [last unloaded: nf_defrag_ipv4]

Pid: 21127, comm: sshd Not tainted 2.6.32-279.el6.x86_64 #1 Red Hat KVM
RIP: 0010:[<ffffffff8131e38e>]  [<ffffffff8131e38e>] tty_insert_flip_string+0x6e/0xd0
RSP: 0018:ffff880164487d78  EFLAGS: 00010202
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000100
RDX: ffff8801833c9978 RSI: ffff8803bb820800 RDI: 0000000000000246
RBP: ffff880164487db8 R08: ffff8801833c91b0 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 0000000000000001 R14: ffff8801833c9800 R15: 0000000000000001
FS:  00007ffff7f507c0(0000) GS:ffff880028200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000018 CR3: 000000015da9c000 CR4: 00000000000006f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process sshd (pid: 21127, threadinfo ffff880164486000, task ffff880411f35500)
Stack:
ffff8803bb820800 0000000000000001 0000000000000000 ffff8801833c9000
<d> ffff8801833c9800 0000000000000001 ffff8803bb820800 ffff8801833c94d0
<d> ffff880164487de8 ffffffff8131f049 ffff8802e8687c80 ffff8801833c9000
Call Trace:
[<ffffffff8131f049>] pty_write+0x39/0x80
[<ffffffff8131931c>] n_tty_write+0x33c/0x460
[<ffffffff81060250>] ? default_wake_function+0x0/0x20
[<ffffffff8100988e>] ? __switch_to+0x26e/0x320
[<ffffffff81315f41>] tty_write+0x1b1/0x2a0
[<ffffffff81318fe0>] ? n_tty_write+0x0/0x460
[<ffffffff8117b068>] vfs_write+0xb8/0x1a0
[<ffffffff8117ba81>] sys_write+0x51/0x90
[<ffffffff8100b0f2>] system_call_fastpath+0x16/0x1b
Code: 00 07 00 00 48 0f 47 f0 48 63 f6 e8 6d fc ff ff 85 c0 41 89 c4 49 8b 9e 88 01 00 00 74 3c 48 98 48 8b 75 c0  
45 01 e5 48 89 45 c8 <48> 63 7b 18 48 89 c2 48 03 7b 08 e8 12 fd f5 ff 48 63 7b 18 48 
RIP  [<ffffffff8131e38e>] tty_insert_flip_string+0x6e/0xd0
RSP <ffff880164487d78>
CR2: 0000000000000018