f2fs: fix NULL pointer dereference in f2fs_submit_page_write()

BUG: kernel NULL pointer dereference, address: 0000000000000014
RIP: 0010:f2fs_submit_page_write+0x6cf/0x780 [f2fs]
Call Trace:
<TASK>
? show_regs+0x6e/0x80
? __die+0x29/0x70
? page_fault_oops+0x154/0x4a0
? prb_read_valid+0x20/0x30
? __irq_work_queue_local+0x39/0xd0
? irq_work_queue+0x36/0x70
? do_user_addr_fault+0x314/0x6c0
? exc_page_fault+0x7d/0x190
? asm_exc_page_fault+0x2b/0x30
? f2fs_submit_page_write+0x6cf/0x780 [f2fs]
? f2fs_submit_page_write+0x736/0x780 [f2fs]
do_write_page+0x50/0x170 [f2fs]
f2fs_outplace_write_data+0x61/0xb0 [f2fs]
f2fs_do_write_data_page+0x3f8/0x660 [f2fs]
f2fs_write_single_data_page+0x5bb/0x7a0 [f2fs]
f2fs_write_cache_pages+0x3da/0xbe0 [f2fs]
...
It is possible that other threads have added this fio to io->bio
and submitted the io->bio before entering f2fs_submit_page_write().
At this point io->bio = NULL.
If is_end_zone_blkaddr(sbi, fio->new_blkaddr) of this fio is true,
then an NULL pointer dereference error occurs at bio_get(io->bio).
The original code for determining zone end was after "out:",
which would have missed some fio who is zone end. I've moved
 this code before "skip:" to make sure it's done for each fio.

Fixes: e067dc3c ("f2fs: maintain six open zones for zoned devices")
Signed-off-by: Wenjie Qi <qwjhust@gmail.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -1080,10 +1080,6 @@ void f2fs_submit_page_write(struct f2fs_io_info *fio)
 	io->last_block_in_bio = fio->new_blkaddr;
 
 	trace_f2fs_submit_page_write(fio->page, fio);
-skip:
-	if (fio->in_list)
-		goto next;
-out:
 #ifdef CONFIG_BLK_DEV_ZONED
 	if (f2fs_sb_has_blkzoned(sbi) && btype < META &&
 			is_end_zone_blkaddr(sbi, fio->new_blkaddr)) {
@@ -1096,6 +1092,10 @@ void f2fs_submit_page_write(struct f2fs_io_info *fio)
 		__submit_merged_bio(io);
 	}
 #endif
+skip:
+	if (fio->in_list)
+		goto next;
+out:
 	if (is_sbi_flag_set(sbi, SBI_IS_SHUTDOWN) ||
 				!f2fs_is_checkpoint_ready(sbi))
 		__submit_merged_bio(io);