Commit a9af3fdc authored Apr 25, 2018 by Chao Yu Committed by Jaegeuk Kim May 31, 2018

f2fs: fix potential overflow



In build_sit_entries(), if valid_blocks in SIT block is smaller than
valid_blocks in journal, for below calculation:

sbi->discard_blks += old_valid_blocks - se->valid_blocks;

There will be two times potential overflow:
- old_valid_blocks - se->valid_blocks will overflow, and be a very
large number.
- sbi->discard_blks += result will overflow again, comes out a correct
result accidently.

Anyway, it should be fixed.

Fixes: d600af23 ("f2fs: avoid unneeded loop in build_sit_entries")
Fixes: 1f43e2ad ("f2fs: introduce CP_TRIMMED_FLAG to avoid unneeded discard")
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

parent b2532c69

fs/f2fs/segment.c

+7 −4

Original line number	Diff line number	Diff line
		@@ -3714,14 +3714,17 @@ static int build_sit_entries(struct f2fs_sb_info *sbi)
		} else {
		memcpy(se->discard_map, se->cur_valid_map,
		SIT_VBLOCK_MAP_SIZE);
		sbi->discard_blks += old_valid_blocks -
		se->valid_blocks;
		sbi->discard_blks += old_valid_blocks;
		sbi->discard_blks -= se->valid_blocks;
		}
		}

		if (sbi->segs_per_sec > 1)
		if (sbi->segs_per_sec > 1) {
		get_sec_entry(sbi, start)->valid_blocks +=
		se->valid_blocks - old_valid_blocks;
		se->valid_blocks;
		get_sec_entry(sbi, start)->valid_blocks -=
		old_valid_blocks;
		}
		}
		up_read(&curseg->journal_rwsem);

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