f2fs: avoid out-of-range memory access

blkoff_off might over 512 due to fs corrupt or security
vulnerability. That should be checked before being using.

Use ENTRIES_IN_SUM to protect invalid value in cur_data_blkoff.

Signed-off-by: Ocean Chen <oceanchen@google.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 2d1d7ba..a661ac3 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -3447,6 +3447,11 @@
 		seg_i = CURSEG_I(sbi, i);
 		segno = le32_to_cpu(ckpt->cur_data_segno[i]);
 		blk_off = le16_to_cpu(ckpt->cur_data_blkoff[i]);
+		if (blk_off > ENTRIES_IN_SUM) {
+			f2fs_bug_on(sbi, 1);
+			f2fs_put_page(page, 1);
+			return -EFAULT;
+		}
 		seg_i->next_segno = segno;
 		reset_curseg(sbi, i, 0);
 		seg_i->alloc_type = ckpt->alloc_type[i];