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/[email protected]
Fixes: cf76c78 ("ocfs2: don't put and assigning null to bh allocated outside")
Signed-off-by: Lizhi Xu <[email protected]>
Signed-off-by: Joseph Qi <[email protected]>
Reviewed-by: Joseph Qi <[email protected]>
Reported-by: Heming Zhao <[email protected]>
Suggested-by: Heming Zhao <[email protected]>
Cc: <[email protected]>	[4.20+]
Cc: Changwei Ge <[email protected]>
Cc: Gang He <[email protected]>
Cc: Joel Becker <[email protected]>
Cc: Jun Piao <[email protected]>
Cc: Junxiao Bi <[email protected]>
Cc: Mark Fasheh <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Lizhi Xu

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);