f2fs: fix panic during f2fs_resize_fs()

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

f2fs: fix panic during f2fs_resize_fs()

f2fs_resize_fs() hangs in below callstack with testcase:

- mkfs 16GB image & mount image

- dd 8GB fileA

- dd 8GB fileB

- sync

- rm fileA

- sync

- resize filesystem to 8GB

kernel BUG at segment.c:2484!

Call Trace:

allocate_segment_by_default+0x92/0xf0 [f2fs]

f2fs_allocate_data_block+0x44b/0x7e0 [f2fs]

do_write_page+0x5a/0x110 [f2fs]

f2fs_outplace_write_data+0x55/0x100 [f2fs]

f2fs_do_write_data_page+0x392/0x850 [f2fs]

move_data_page+0x233/0x320 [f2fs]

do_garbage_collect+0x14d9/0x1660 [f2fs]

free_segment_range+0x1f7/0x310 [f2fs]

f2fs_resize_fs+0x118/0x330 [f2fs]

__f2fs_ioctl+0x487/0x3680 [f2fs]

__x64_sys_ioctl+0x8e/0xd0

do_syscall_64+0x33/0x80

entry_SYSCALL_64_after_hwframe+0x44/0xa9

The root cause is we forgot to check that whether we have enough space

in resized filesystem to store all valid blocks in before-resizing

filesystem, then allocator will run out-of-space during block migration

in free_segment_range().