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f2fs: fix potential overflow

PATCH New Chao Yu 1 participant 1 message Apr 25, 2018 F2FS file system

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Chao Yu

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PATCH 1/1 f2fs: fix potential overflow

From: Chao Yu <[email protected]>

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 d600af236da5 ("f2fs: avoid unneeded loop in build_sit_entries")
Fixes 1f43e2ad7bff ("f2fs: introduce CP_TRIMMED_FLAG to avoid unneeded discard")
Signed-off-by Chao Yu <[email protected]>
---
 fs/f2fs/segment.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)
fs/f2fs/segment.c +7 -4
index a55647f61232..49fce2b56017 100644
@@ -3692,14 +3692,17 @@ 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);
Signature · 1 line
2.16.2.17.g38e79b1fd