ocfs2: fix possible null-ptr-deref in ocfs2_set_buffer_uptodate

When doing cleanup, if flags without OCFS2_BH_READAHEAD, it may trigger
NULL pointer dereference in the following ocfs2_set_buffer_uptodate() if
bh is NULL.

Link: https://lkml.kernel.org/r/20240902023636.1843422-3-joseph.qi@linux.alibaba.com
Fixes: cf76c785 ("ocfs2: don't put and assigning null to bh allocated outside")
Signed-off-by: Lizhi Xu <lizhi.xu@windriver.com>
Signed-off-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Reported-by: Heming Zhao <heming.zhao@suse.com>
Suggested-by: Heming Zhao <heming.zhao@suse.com>
Cc: <stable@vger.kernel.org>	[4.20+]
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Gang He <ghe@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Jun Piao <piaojun@huawei.com>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Mark Fasheh <mark@fasheh.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/ocfs2/buffer_head_io.c

@@ -388,7 +388,8 @@ int ocfs2_read_blocks(struct ocfs2_caching_info *ci, u64 block, int nr,
 		/* Always set the buffer in the cache, even if it was
 		 * a forced read, or read-ahead which hasn't yet
 		 * completed. */
-		ocfs2_set_buffer_uptodate(ci, bh);
+		if (bh)
+			ocfs2_set_buffer_uptodate(ci, bh);
 	}
 	ocfs2_metadata_cache_io_unlock(ci);