[PATCH v3 1/2] md: Fix overflow in is_mddev_idle

[linan666@xxxxxxxxxxxxxxx]

From: Li Nan <linan122@xxxxxxxxxx>

UBSAN reports this problem:

  UBSAN: Undefined behaviour in drivers/md/md.c:8175:15
  signed integer overflow:
  -2147483291 - 2072033152 cannot be represented in type 'int'
  Call trace:
   dump_backtrace+0x0/0x310
   show_stack+0x28/0x38
   dump_stack+0xec/0x15c
   ubsan_epilogue+0x18/0x84
   handle_overflow+0x14c/0x19c
   __ubsan_handle_sub_overflow+0x34/0x44
   is_mddev_idle+0x338/0x3d8
   md_do_sync+0x1bb8/0x1cf8
   md_thread+0x220/0x288
   kthread+0x1d8/0x1e0
   ret_from_fork+0x10/0x18

'curr_events' will overflow when stat accum or 'sync_io' is greater than
INT_MAX.

Fix it by changing sync_io, last_events and curr_events to 64bit.

Signed-off-by: Li Nan <linan122@xxxxxxxxxx>
---
 drivers/md/md.h        | 4 ++--
 include/linux/blkdev.h | 2 +-
 drivers/md/md.c        | 7 ++++---
 3 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/md/md.h b/drivers/md/md.h
index ade83af123a2..1a4f976951c1 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -50,7 +50,7 @@ struct md_rdev {
 
 	sector_t sectors;		/* Device size (in 512bytes sectors) */
 	struct mddev *mddev;		/* RAID array if running */
-	int last_events;		/* IO event timestamp */
+	long long last_events;		/* IO event timestamp */
 
 	/*
 	 * If meta_bdev is non-NULL, it means that a separate device is
@@ -584,7 +584,7 @@ extern void mddev_unlock(struct mddev *mddev);
 
 static inline void md_sync_acct(struct block_device *bdev, unsigned long nr_sectors)
 {
-	atomic_add(nr_sectors, &bdev->bd_disk->sync_io);
+	atomic64_add(nr_sectors, &bdev->bd_disk->sync_io);
 }
 
 static inline void md_sync_acct_bio(struct bio *bio, unsigned long nr_sectors)
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 3f8a21cd9233..d28b98adf457 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -170,7 +170,7 @@ struct gendisk {
 	struct list_head slave_bdevs;
 #endif
 	struct timer_rand_state *random;
-	atomic_t sync_io;		/* RAID */
+	atomic64_t sync_io;		/* RAID */
 	struct disk_events *ev;
 
 #ifdef CONFIG_BLK_DEV_ZONED
diff --git a/drivers/md/md.c b/drivers/md/md.c
index c94373d64f2c..a6829ea5b560 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -8496,14 +8496,15 @@ static int is_mddev_idle(struct mddev *mddev, int init)
 {
 	struct md_rdev *rdev;
 	int idle;
-	int curr_events;
+	long long curr_events;
 
 	idle = 1;
 	rcu_read_lock();
 	rdev_for_each_rcu(rdev, mddev) {
 		struct gendisk *disk = rdev->bdev->bd_disk;
-		curr_events = (int)part_stat_read_accum(disk->part0, sectors) -
-			      atomic_read(&disk->sync_io);
+		curr_events =
+			(long long)part_stat_read_accum(disk->part0, sectors) -
+			atomic64_read(&disk->sync_io);
 		/* sync IO will cause sync_io to increase before the disk_stats
 		 * as sync_io is counted when a request starts, and
 		 * disk_stats is counted when it completes.
-- 
2.39.2