efivar: fix oops in efivar_update_sysfs_entries() caused by memory reuse

efivar: fix oops in efivar_update_sysfs_entries() caused by memory reuse

The loop in efivar_update_sysfs_entries() reuses the same allocation for
entries each time it calls efivar_create_sysfs_entry(entry).  This is
wrong because efivar_create_sysfs_entry() expects to keep the memory it
was passed, so the caller may not free it (and may not pass the same
memory in multiple times).  This leads to the oops below.  Fix by
getting a new allocation each time we go around the loop.

---[ end trace ba4907d5c519d111 ]---
BUG: unable to handle kernel NULL pointer dereference at           (null)
IP: [<ffffffff8142f81f>] efivar_entry_find+0x14f/0x2d0
PGD 0
Oops: 0000 [#2] SMP
Modules linked in: oops(OF+) ebtable_nat ebtables xt_CHECKSUM [...]
CPU: 0 PID: 301 Comm: kworker/0:2 Tainted: GF     D    O 3.9.0+ #1
Hardware name: LENOVO 4291EV7/4291EV7, BIOS 8DET52WW (1.22 ) 09/15/2011
Workqueue: events efivar_update_sysfs_entries
task: ffff8801955920c0 ti: ffff88019413e000 task.ti: ffff88019413e000
RIP: 0010:[<ffffffff8142f81f>]  [<ffffffff8142f81f>] efivar_entry_find+0x14f/0x2d0
RSP: 0018:ffff88019413fa48  EFLAGS: 00010006
RAX: 0000000000000000 RBX: ffff880195d87c00 RCX: ffffffff81ab6f60
RDX: ffff88019413fb88 RSI: 0000000000000400 RDI: ffff880196254000
RBP: ffff88019413fbd8 R08: 0000000000000000 R09: ffff8800dad99037
R10: ffff880195d87c00 R11: 0000000000000430 R12: ffffffff81ab6f60
R13: fffffffffffff7d8 R14: ffff880196254000 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff88019e200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000001a0b000 CR4: 00000000000407f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Stack:
 ffff88019413fb78 ffff88019413fb88 ffffffff81e85d60 03000000972b5c00
 ffff88019413fa29 ffffffff81e85d60 ffff88019413fbfb 0000000197087280
 00000000000000fe 0000000000000001 ffffffff81e85dd9 ffff880197087280
Call Trace:
 [<ffffffff81254371>] ? idr_get_empty_slot+0x131/0x240
 [<ffffffff8125b6d2>] ? put_dec+0x72/0x90
 [<ffffffff81158e40>] ? cache_alloc_refill+0x170/0x2f0
 [<ffffffff81430420>] efivar_update_sysfs_entry+0x150/0x220
 [<ffffffff8103dd29>] ? efi_call2+0x9/0x70
 [<ffffffff8103d787>] ? virt_efi_get_next_variable+0x47/0x1b0
 [<ffffffff8115a8df>] ? kmem_cache_alloc_trace+0x1af/0x1c0
 [<ffffffff81430033>] efivar_init+0x2c3/0x380
 [<ffffffff814302d0>] ? efivar_delete+0xd0/0xd0
 [<ffffffff8143111f>] efivar_update_sysfs_entries+0x6f/0x90
 [<ffffffff810605f3>] process_one_work+0x183/0x490
 [<ffffffff81061780>] worker_thread+0x120/0x3a0
 [<ffffffff81061660>] ? manage_workers+0x160/0x160
 [<ffffffff8106752e>] kthread+0xce/0xe0
 [<ffffffff81067460>] ? kthread_freezable_should_stop+0x70/0x70
 [<ffffffff81543c5c>] ret_from_fork+0x7c/0xb0
 [<ffffffff81067460>] ? kthread_freezable_should_stop+0x70/0x70
Code: 8d 55 b0 48 8d 45 a0 49 81 ed 28 08 00 00 48 89 95 78 fe [...]
RIP  [<ffffffff8142f81f>] efivar_entry_find+0x14f/0x2d0
 RSP <ffff88019413fa48>
CR2: 0000000000000000
---[ end trace ba4907d5c519d112 ]---

Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Tomoki Sekiyama <tomoki.sekiyama@hds.com>
Signed-off-by: Seiji Aguchi <seiji.aguchi@hds.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>