ocfs2: fix uninitialized value in ocfs2_file_read_iter()

Syzbot has reported the following KMSAN splat:

BUG: KMSAN: uninit-value in ocfs2_file_read_iter+0x9a4/0xf80
 ocfs2_file_read_iter+0x9a4/0xf80
 __io_read+0x8d4/0x20f0
 io_read+0x3e/0xf0
 io_issue_sqe+0x42b/0x22c0
 io_wq_submit_work+0xaf9/0xdc0
 io_worker_handle_work+0xd13/0x2110
 io_wq_worker+0x447/0x1410
 ret_from_fork+0x6f/0x90
 ret_from_fork_asm+0x1a/0x30

Uninit was created at:
 __alloc_pages_noprof+0x9a7/0xe00
 alloc_pages_mpol_noprof+0x299/0x990
 alloc_pages_noprof+0x1bf/0x1e0
 allocate_slab+0x33a/0x1250
 ___slab_alloc+0x12ef/0x35e0
 kmem_cache_alloc_bulk_noprof+0x486/0x1330
 __io_alloc_req_refill+0x84/0x560
 io_submit_sqes+0x172f/0x2f30
 __se_sys_io_uring_enter+0x406/0x41c0
 __x64_sys_io_uring_enter+0x11f/0x1a0
 x64_sys_call+0x2b54/0x3ba0
 do_syscall_64+0xcd/0x1e0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Since an instance of 'struct kiocb' may be passed from the block layer
with 'private' field uninitialized, introduce 'ocfs2_iocb_init_rw_locked()'
and use it from where 'ocfs2_dio_end_io()' might take care, i.e. in
'ocfs2_file_read_iter()' and 'ocfs2_file_write_iter()'.

Link: https://lkml.kernel.org/r/20241029091736.1501946-1-dmantipov@yandex.ru
Fixes: 7cdfc3a ("ocfs2: Remember rw lock level during direct io")
Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Reported-by: syzbot+a73e253cca4f0230a5a5@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=a73e253cca4f0230a5a5
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Joseph Qi <jiangqi903@gmail.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Jun Piao <piaojun@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/ocfs2/aops.h

@@ -70,6 +70,8 @@ enum ocfs2_iocb_lock_bits {
 	OCFS2_IOCB_NUM_LOCKS
 };
 
+#define ocfs2_iocb_init_rw_locked(iocb) \
+	(iocb->private = NULL)
 #define ocfs2_iocb_clear_rw_locked(iocb) \
 	clear_bit(OCFS2_IOCB_RW_LOCK, (unsigned long *)&iocb->private)
 #define ocfs2_iocb_rw_locked_level(iocb) \

fs/ocfs2/file.c

@@ -2398,6 +2398,8 @@ static ssize_t ocfs2_file_write_iter(struct kiocb *iocb,
 	} else
 		inode_lock(inode);
 
+	ocfs2_iocb_init_rw_locked(iocb);
+
 	/*
 	 * Concurrent O_DIRECT writes are allowed with
 	 * mount_option "coherency=buffered".
@@ -2544,6 +2546,8 @@ static ssize_t ocfs2_file_read_iter(struct kiocb *iocb,
 	if (!direct_io && nowait)
 		return -EOPNOTSUPP;
 
+	ocfs2_iocb_init_rw_locked(iocb);
+
 	/*
 	 * buffered reads protect themselves in ->read_folio().  O_DIRECT reads
 	 * need locks to protect pending reads from racing with truncate.