f2fs: fix to do sanity check on node footer in {read,write}_end_io

In the Linux kernel, the following vulnerability has been resolved:

f2fs: fix to do sanity check on node footer in {read,write}_end_io

-----------[ cut here ]------------

kernel BUG at fs/f2fs/data.c:358!

Call Trace:

<IRQ>

blk_update_request+0x5eb/0xe70 block/blk-mq.c:987

blk_mq_end_request+0x3e/0x70 block/blk-mq.c:1149

blk_complete_reqs block/blk-mq.c:1224 [inline]

blk_done_softirq+0x107/0x160 block/blk-mq.c:1229

handle_softirqs+0x283/0x870 kernel/softirq.c:579

__do_softirq kernel/softirq.c:613 [inline]

invoke_softirq kernel/softirq.c:453 [inline]

__irq_exit_rcu+0xca/0x1f0 kernel/softirq.c:680

irq_exit_rcu+0x9/0x30 kernel/softirq.c:696

instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1050 [inline]

sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1050

</IRQ>

In f2fs_write_end_io(), it detects there is inconsistency in between

node page index (nid) and footer.nid of node page.

If footer of node page is corrupted in fuzzed image, then we load corrupted

node page w/ async method, e.g. f2fs_ra_node_pages() or f2fs_ra_node_page(),

in where we won't do sanity check on node footer, once node page becomes

dirty, we will encounter this bug after node page writeback.