This looks like a kernel bug.  dmesg output corresponding to the keyctl call:

[172406.924622] BUG: unable to handle kernel NULL pointer dereference at 0000000
000000004
[172406.924632] IP: [<ffffffff8035f44b>] call_sbin_request_key+0x2db/0x2f0
[172406.924646] PGD 33157067 PUD a946067 PMD 0 
[172406.924654] Oops: 0000 [1] SMP 
[172406.924659] CPU 1 
[172406.924663] Modules linked in: nls_iso8859_1 nls_cp437 vfat fat usb_storage libusual tun nfs lockd nfs_acl sunrpc iwl3945 af_packet i915 drm binfmt_misc rfcomm sco bridge stp bnep l2cap bluetooth ppdev acpi_cpufreq cpufreq_userspace cpufreq_conservative cpufreq_stats cpufreq_ondemand freq_table cpufreq_powersave sbs sbshc container pci_slot wmi iptable_filter ip_tables x_tables ipv6 parport_pc lp parport loop joydev pcmcia thinkpad_acpi arc4 ecb nvram snd_hda_intel snd_pcm_oss snd_mixer_oss snd_pcm evdev serio_raw pcspkr psmouse rfkill yenta_socket rsrc_nonstatic mac80211 pcmcia_core snd_seq_dummy iTCO_wdt iTCO_vendor_support led_class snd_seq_oss battery cfg80211 video ac nsc_ircc snd_seq_midi output irda snd_rawmidi crc_ccitt snd_seq_midi_event snd_seq snd_timer snd_seq_device snd soundcore snd_page_alloc button shpchp pci_hotplug intel_agp ext3 jbd mbcache sha256_generic aes_x86_64 aes_generic cbc sr_mod cdrom sd_mod crc_t10dif sg ata_piix pata_acpi ata_generic ahci libata scsi_mod ehci_hcd uhci_hcd usbcore e1000e dock dm_crypt crypto_blkcipher dm_mirror dm_log dm_snapshot dm_mod thermal processor fan fbcon tileblit font bitblit softcursor fuse [last unloaded: iwl3945]
[172406.924834] Pid: 9408, comm: keyctl Not tainted 2.6.27-8-generic #1
[172406.924839] RIP: 0010:[<ffffffff8035f44b>]  [<ffffffff8035f44b>] call_sbin_request_key+0x2db/0x2f0
[172406.924848] RSP: 0018:ffff880010d9fd18  EFLAGS: 00010246
[172406.924852] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
[172406.924857] RDX: ffff880010d9fd95 RSI: 00000000fffffffc RDI: 0000000000000001
[172406.924861] RBP: ffff880010d9fe58 R08: 00000000ffffffff R09: 0000000000000001
[172406.924865] R10: ffff880010d9fc38 R11: ffff880090d9fd93 R12: ffff880010d9fd88
[172406.924869] R13: ffff88003d04d900 R14: ffff88001a873350 R15: ffff880021499670
[172406.924875] FS:  00007f3d471d26e0(0000) GS:ffff88003f002880(0000) knlGS:0000000000000000
[172406.924880] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[172406.924884] CR2: 0000000000000004 CR3: 0000000010081000 CR4: 00000000000006a0
[172406.924889] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[172406.924893] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[172406.924898] Process keyctl (pid: 9408, threadinfo ffff880010d9e000, task ffff880021499670)
[172406.924902] Stack:  ffff880010d9fd68 ffffffff805fbf91 ffff880010d9fd94 ffff88001f5f33c0
[172406.924912]  0000000000000031 ffff88001f5f3900 ffff880010d9fd68 ffffffff80501116
[172406.924920]  ffff88001f5f3904 ffffffff805010c9 ffff880010d9fda8 ffffffff8035b011
[172406.924928] Call Trace:
[172406.924936]  [<ffffffff80501116>] ? mutex_lock+0x16/0x30
[172406.924941]  [<ffffffff805010c9>] ? mutex_unlock+0x9/0x20
[172406.924948]  [<ffffffff8035b011>] ? __key_instantiate_and_link+0xd1/0xf0
[172406.924954]  [<ffffffff8035b0bb>] ? key_instantiate_and_link+0x8b/0x90
[172406.924960]  [<ffffffff8035fa32>] ? request_key_auth_new+0x202/0x240
[172406.924966]  [<ffffffff8035ef25>] construct_key+0xa5/0x110
[172406.924972]  [<ffffffff8035f08c>] request_key_and_link+0xfc/0x130
[172406.924979]  [<ffffffff8035db21>] sys_request_key+0x161/0x1a0
[172406.924987]  [<ffffffff8021285a>] system_call_fastpath+0x16/0x1b
[172406.924991] 
[172406.924993] 
[172406.924995] Code: e9 db fd ff ff 0f 1f 00 48 8b bd d8 fe ff ff 31 db e8 ea e8 ff ff 85 c0 79 de eb d7 0f 1f 40 00 49 8b 87 48 04 00 00 48 8b 40 30 <8b> 50 04 e9 c5 fe ff ff 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 
[172406.925063] RIP  [<ffffffff8035f44b>] call_sbin_request_key+0x2db/0x2f0
[172406.925071]  RSP <ffff880010d9fd18>
[172406.925074] CR2: 0000000000000004
[172406.925095] ---[ end trace 52139f9169d6eb43 ]---