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Subject[PATCH v3 1/3] md: Fix undefined behaviour in is_mddev_idle
Date
UBSAN reports this problem:

[ 5984.281385] UBSAN: Undefined behaviour in drivers/md/md.c:8175:15
[ 5984.281390] signed integer overflow:
[ 5984.281393] -2147483291 - 2072033152 cannot be represented in type 'int'
[ 5984.281400] CPU: 25 PID: 1854 Comm: md101_resync Kdump: loaded Not tainted 4.19.90
[ 5984.281404] Hardware name: Huawei TaiShan 200 (Model 5280)/BC82AMDDA
[ 5984.281406] Call trace:
[ 5984.281415] dump_backtrace+0x0/0x310
[ 5984.281418] show_stack+0x28/0x38
[ 5984.281425] dump_stack+0xec/0x15c
[ 5984.281430] ubsan_epilogue+0x18/0x84
[ 5984.281434] handle_overflow+0x14c/0x19c
[ 5984.281439] __ubsan_handle_sub_overflow+0x34/0x44
[ 5984.281445] is_mddev_idle+0x338/0x3d8
[ 5984.281449] md_do_sync+0x1bb8/0x1cf8
[ 5984.281452] md_thread+0x220/0x288
[ 5984.281457] kthread+0x1d8/0x1e0
[ 5984.281461] ret_from_fork+0x10/0x18

When the stat aacum of the disk is greater than INT_MAX, its
value becomes negative after casting to 'int', which may lead
to overflow after subtracting a positive number. In the same
way, when the value of sync_io is greater than INT_MAX,
overflow may also occur. These situations will lead to
undefined behavior.

Otherwise, if the stat accum of the disk is close to INT_MAX
when creating raid arrays, the initial value of last_events
would be set close to INT_MAX when mddev initializes IO
event counters. 'curr_events - rdev->last_events > 64' will
always false during synchronization. If all the disks of mddev
are in this case, is_mddev_idle() will always return 1, which
may cause non-sync IO is very slow.

Fix by using atomic64_t type for sync_io, and using s64 type
for curr_events/last_events.

Signed-off-by: Li Jinlin <lijinlin3@huawei.com>
---
drivers/md/md.c | 6 +++---
drivers/md/md.h | 4 ++--
include/linux/genhd.h | 2 +-
3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 5111ed966947..be73a5ae6864 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -8429,14 +8429,14 @@ static int is_mddev_idle(struct mddev *mddev, int init)
{
struct md_rdev *rdev;
int idle;
- int curr_events;
+ s64 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 = (s64)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.
diff --git a/drivers/md/md.h b/drivers/md/md.h
index 53ea7a6961de..e00d6730da13 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 */
+ s64 last_events; /* IO event timestamp */

/*
* If meta_bdev is non-NULL, it means that a separate device is
@@ -551,7 +551,7 @@ 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/genhd.h b/include/linux/genhd.h
index 74c410263113..efa7884de11b 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -150,7 +150,7 @@ 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_INTEGRITY
struct kobject integrity_kobj;
--
2.27.0
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