As Wenqing Liu reported in bugzilla:

https://bugzilla.kernel.org/show_bug.cgi?id=215657

- Overview
UBSAN: array-index-out-of-bounds in fs/f2fs/segment.c:3460:2 when mount and operate a corrupted image

- Reproduce
tested on kernel 5.17-rc4, 5.17-rc6

1. mkdir test_crash
2. cd test_crash
3. unzip tmp2.zip
4. mkdir mnt
5. ./single_test.sh f2fs 2

- Kernel dump
[   46.434454] loop0: detected capacity change from 0 to 131072
[   46.529839] F2FS-fs (loop0): Mounted with checkpoint version = 7548c2d9
[   46.738319] ================================================================================
[   46.738412] UBSAN: array-index-out-of-bounds in fs/f2fs/segment.c:3460:2
[   46.738475] index 231 is out of range for type 'unsigned int [2]'
[   46.738539] CPU: 2 PID: 939 Comm: umount Not tainted 5.17.0-rc6 #1
[   46.738547] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-1ubuntu1.1 04/01/2014
[   46.738551] Call Trace:
[   46.738556]  <TASK>
[   46.738563]  dump_stack_lvl+0x47/0x5c
[   46.738581]  ubsan_epilogue+0x5/0x50
[   46.738592]  __ubsan_handle_out_of_bounds+0x68/0x80
[   46.738604]  f2fs_allocate_data_block+0xdff/0xe60 [f2fs]
[   46.738819]  do_write_page+0xef/0x210 [f2fs]
[   46.738934]  f2fs_do_write_node_page+0x3f/0x80 [f2fs]
[   46.739038]  __write_node_page+0x2b7/0x920 [f2fs]
[   46.739162]  f2fs_sync_node_pages+0x943/0xb00 [f2fs]
[   46.739293]  f2fs_write_checkpoint+0x7bb/0x1030 [f2fs]
[   46.739405]  kill_f2fs_super+0x125/0x150 [f2fs]
[   46.739507]  deactivate_locked_super+0x60/0xc0
[   46.739517]  deactivate_super+0x70/0xb0
[   46.739524]  cleanup_mnt+0x11a/0x200
[   46.739532]  __cleanup_mnt+0x16/0x20
[   46.739538]  task_work_run+0x67/0xa0
[   46.739547]  exit_to_user_mode_prepare+0x18c/0x1a0
[   46.739559]  syscall_exit_to_user_mode+0x26/0x40
[   46.739568]  do_syscall_64+0x46/0xb0
[   46.739584]  entry_SYSCALL_64_after_hwframe+0x44/0xae

The root cause is we missed to do sanity check on curseg->alloc_type,
result in out-of-bound accessing on sbi->block_count[] array, fix it.
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>