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From: Jan Kara <jack@suse.cz>
To: Jens Axboe <axboe@kernel.dk>
Cc: <linux-block@vger.kernel.org>,
	Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
	Jan Kara <jack@suse.cz>
Subject: [PATCH 02/16] block/loop: Use global lock for ioctl() operation.
Date: Thu,  8 Nov 2018 14:01:02 +0100	[thread overview]
Message-ID: <20181108130116.12140-3-jack@suse.cz> (raw)
In-Reply-To: <20181108130116.12140-1-jack@suse.cz>

From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

syzbot is reporting NULL pointer dereference [1] which is caused by
race condition between ioctl(loop_fd, LOOP_CLR_FD, 0) versus
ioctl(other_loop_fd, LOOP_SET_FD, loop_fd) due to traversing other
loop devices at loop_validate_file() without holding corresponding
lo->lo_ctl_mutex locks.

Since ioctl() request on loop devices is not frequent operation, we don't
need fine grained locking. Let's use global lock in order to allow safe
traversal at loop_validate_file().

Note that syzbot is also reporting circular locking dependency between
bdev->bd_mutex and lo->lo_ctl_mutex [2] which is caused by calling
blkdev_reread_part() with lock held. This patch does not address it.

[1] https://syzkaller.appspot.com/bug?id=f3cfe26e785d85f9ee259f385515291d21bd80a3
[2] https://syzkaller.appspot.com/bug?id=bf154052f0eea4bc7712499e4569505907d15889

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+bf89c128e05dd6c62523@syzkaller.appspotmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 drivers/block/loop.c | 58 ++++++++++++++++++++++++++--------------------------
 drivers/block/loop.h |  1 -
 2 files changed, 29 insertions(+), 30 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index a29ef169f360..63008e879771 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -84,6 +84,7 @@
 
 static DEFINE_IDR(loop_index_idr);
 static DEFINE_MUTEX(loop_index_mutex);
+static DEFINE_MUTEX(loop_ctl_mutex);
 
 static int max_part;
 static int part_shift;
@@ -1046,7 +1047,7 @@ static int loop_clr_fd(struct loop_device *lo)
 	 */
 	if (atomic_read(&lo->lo_refcnt) > 1) {
 		lo->lo_flags |= LO_FLAGS_AUTOCLEAR;
-		mutex_unlock(&lo->lo_ctl_mutex);
+		mutex_unlock(&loop_ctl_mutex);
 		return 0;
 	}
 
@@ -1099,12 +1100,12 @@ static int loop_clr_fd(struct loop_device *lo)
 	if (!part_shift)
 		lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;
 	loop_unprepare_queue(lo);
-	mutex_unlock(&lo->lo_ctl_mutex);
+	mutex_unlock(&loop_ctl_mutex);
 	/*
-	 * Need not hold lo_ctl_mutex to fput backing file.
-	 * Calling fput holding lo_ctl_mutex triggers a circular
+	 * Need not hold loop_ctl_mutex to fput backing file.
+	 * Calling fput holding loop_ctl_mutex triggers a circular
 	 * lock dependency possibility warning as fput can take
-	 * bd_mutex which is usually taken before lo_ctl_mutex.
+	 * bd_mutex which is usually taken before loop_ctl_mutex.
 	 */
 	fput(filp);
 	return 0;
@@ -1209,7 +1210,7 @@ loop_get_status(struct loop_device *lo, struct loop_info64 *info)
 	int ret;
 
 	if (lo->lo_state != Lo_bound) {
-		mutex_unlock(&lo->lo_ctl_mutex);
+		mutex_unlock(&loop_ctl_mutex);
 		return -ENXIO;
 	}
 
@@ -1228,10 +1229,10 @@ loop_get_status(struct loop_device *lo, struct loop_info64 *info)
 		       lo->lo_encrypt_key_size);
 	}
 
-	/* Drop lo_ctl_mutex while we call into the filesystem. */
+	/* Drop loop_ctl_mutex while we call into the filesystem. */
 	path = lo->lo_backing_file->f_path;
 	path_get(&path);
-	mutex_unlock(&lo->lo_ctl_mutex);
+	mutex_unlock(&loop_ctl_mutex);
 	ret = vfs_getattr(&path, &stat, STATX_INO, AT_STATX_SYNC_AS_STAT);
 	if (!ret) {
 		info->lo_device = huge_encode_dev(stat.dev);
@@ -1323,7 +1324,7 @@ loop_get_status_old(struct loop_device *lo, struct loop_info __user *arg) {
 	int err;
 
 	if (!arg) {
-		mutex_unlock(&lo->lo_ctl_mutex);
+		mutex_unlock(&loop_ctl_mutex);
 		return -EINVAL;
 	}
 	err = loop_get_status(lo, &info64);
@@ -1341,7 +1342,7 @@ loop_get_status64(struct loop_device *lo, struct loop_info64 __user *arg) {
 	int err;
 
 	if (!arg) {
-		mutex_unlock(&lo->lo_ctl_mutex);
+		mutex_unlock(&loop_ctl_mutex);
 		return -EINVAL;
 	}
 	err = loop_get_status(lo, &info64);
@@ -1399,7 +1400,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
 	struct loop_device *lo = bdev->bd_disk->private_data;
 	int err;
 
-	err = mutex_lock_killable_nested(&lo->lo_ctl_mutex, 1);
+	err = mutex_lock_killable_nested(&loop_ctl_mutex, 1);
 	if (err)
 		goto out_unlocked;
 
@@ -1411,7 +1412,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
 		err = loop_change_fd(lo, bdev, arg);
 		break;
 	case LOOP_CLR_FD:
-		/* loop_clr_fd would have unlocked lo_ctl_mutex on success */
+		/* loop_clr_fd would have unlocked loop_ctl_mutex on success */
 		err = loop_clr_fd(lo);
 		if (!err)
 			goto out_unlocked;
@@ -1424,7 +1425,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
 		break;
 	case LOOP_GET_STATUS:
 		err = loop_get_status_old(lo, (struct loop_info __user *) arg);
-		/* loop_get_status() unlocks lo_ctl_mutex */
+		/* loop_get_status() unlocks loop_ctl_mutex */
 		goto out_unlocked;
 	case LOOP_SET_STATUS64:
 		err = -EPERM;
@@ -1434,7 +1435,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
 		break;
 	case LOOP_GET_STATUS64:
 		err = loop_get_status64(lo, (struct loop_info64 __user *) arg);
-		/* loop_get_status() unlocks lo_ctl_mutex */
+		/* loop_get_status() unlocks loop_ctl_mutex */
 		goto out_unlocked;
 	case LOOP_SET_CAPACITY:
 		err = -EPERM;
@@ -1454,7 +1455,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
 	default:
 		err = lo->ioctl ? lo->ioctl(lo, cmd, arg) : -EINVAL;
 	}
-	mutex_unlock(&lo->lo_ctl_mutex);
+	mutex_unlock(&loop_ctl_mutex);
 
 out_unlocked:
 	return err;
@@ -1571,7 +1572,7 @@ loop_get_status_compat(struct loop_device *lo,
 	int err;
 
 	if (!arg) {
-		mutex_unlock(&lo->lo_ctl_mutex);
+		mutex_unlock(&loop_ctl_mutex);
 		return -EINVAL;
 	}
 	err = loop_get_status(lo, &info64);
@@ -1588,19 +1589,19 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode,
 
 	switch(cmd) {
 	case LOOP_SET_STATUS:
-		err = mutex_lock_killable(&lo->lo_ctl_mutex);
+		err = mutex_lock_killable(&loop_ctl_mutex);
 		if (!err) {
 			err = loop_set_status_compat(lo,
 						     (const struct compat_loop_info __user *)arg);
-			mutex_unlock(&lo->lo_ctl_mutex);
+			mutex_unlock(&loop_ctl_mutex);
 		}
 		break;
 	case LOOP_GET_STATUS:
-		err = mutex_lock_killable(&lo->lo_ctl_mutex);
+		err = mutex_lock_killable(&loop_ctl_mutex);
 		if (!err) {
 			err = loop_get_status_compat(lo,
 						     (struct compat_loop_info __user *)arg);
-			/* loop_get_status() unlocks lo_ctl_mutex */
+			/* loop_get_status() unlocks loop_ctl_mutex */
 		}
 		break;
 	case LOOP_SET_CAPACITY:
@@ -1647,7 +1648,7 @@ static void __lo_release(struct loop_device *lo)
 	if (atomic_dec_return(&lo->lo_refcnt))
 		return;
 
-	mutex_lock(&lo->lo_ctl_mutex);
+	mutex_lock(&loop_ctl_mutex);
 	if (lo->lo_flags & LO_FLAGS_AUTOCLEAR) {
 		/*
 		 * In autoclear mode, stop the loop thread
@@ -1665,7 +1666,7 @@ static void __lo_release(struct loop_device *lo)
 		blk_mq_unfreeze_queue(lo->lo_queue);
 	}
 
-	mutex_unlock(&lo->lo_ctl_mutex);
+	mutex_unlock(&loop_ctl_mutex);
 }
 
 static void lo_release(struct gendisk *disk, fmode_t mode)
@@ -1711,10 +1712,10 @@ static int unregister_transfer_cb(int id, void *ptr, void *data)
 	struct loop_device *lo = ptr;
 	struct loop_func_table *xfer = data;
 
-	mutex_lock(&lo->lo_ctl_mutex);
+	mutex_lock(&loop_ctl_mutex);
 	if (lo->lo_encryption == xfer)
 		loop_release_xfer(lo);
-	mutex_unlock(&lo->lo_ctl_mutex);
+	mutex_unlock(&loop_ctl_mutex);
 	return 0;
 }
 
@@ -1895,7 +1896,6 @@ static int loop_add(struct loop_device **l, int i)
 	if (!part_shift)
 		disk->flags |= GENHD_FL_NO_PART_SCAN;
 	disk->flags |= GENHD_FL_EXT_DEVT;
-	mutex_init(&lo->lo_ctl_mutex);
 	atomic_set(&lo->lo_refcnt, 0);
 	lo->lo_number		= i;
 	spin_lock_init(&lo->lo_lock);
@@ -2008,21 +2008,21 @@ static long loop_control_ioctl(struct file *file, unsigned int cmd,
 		ret = loop_lookup(&lo, parm);
 		if (ret < 0)
 			break;
-		ret = mutex_lock_killable(&lo->lo_ctl_mutex);
+		ret = mutex_lock_killable(&loop_ctl_mutex);
 		if (ret)
 			break;
 		if (lo->lo_state != Lo_unbound) {
 			ret = -EBUSY;
-			mutex_unlock(&lo->lo_ctl_mutex);
+			mutex_unlock(&loop_ctl_mutex);
 			break;
 		}
 		if (atomic_read(&lo->lo_refcnt) > 0) {
 			ret = -EBUSY;
-			mutex_unlock(&lo->lo_ctl_mutex);
+			mutex_unlock(&loop_ctl_mutex);
 			break;
 		}
 		lo->lo_disk->private_data = NULL;
-		mutex_unlock(&lo->lo_ctl_mutex);
+		mutex_unlock(&loop_ctl_mutex);
 		idr_remove(&loop_index_idr, lo->lo_number);
 		loop_remove(lo);
 		break;
diff --git a/drivers/block/loop.h b/drivers/block/loop.h
index 4d42c7af7de7..af75a5ee4094 100644
--- a/drivers/block/loop.h
+++ b/drivers/block/loop.h
@@ -54,7 +54,6 @@ struct loop_device {
 
 	spinlock_t		lo_lock;
 	int			lo_state;
-	struct mutex		lo_ctl_mutex;
 	struct kthread_worker	worker;
 	struct task_struct	*worker_task;
 	bool			use_dio;
-- 
2.16.4

  parent reply	other threads:[~2018-11-08 13:01 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-08 13:01 [PATCH 0/16 v3] loop: Fix oops and possible deadlocks Jan Kara
2018-11-08 13:01 ` [PATCH 01/16] block/loop: Don't grab "struct file" for vfs_getattr() operation Jan Kara
2018-11-08 13:01 ` Jan Kara [this message]
2018-11-08 13:01 ` [PATCH 03/16] loop: Fold __loop_release into loop_release Jan Kara
2018-11-08 13:01 ` [PATCH 04/16] loop: Get rid of loop_index_mutex Jan Kara
2018-11-08 13:01 ` [PATCH 05/16] loop: Push lo_ctl_mutex down into individual ioctls Jan Kara
2018-11-08 13:01 ` [PATCH 06/16] loop: Split setting of lo_state from loop_clr_fd Jan Kara
2018-11-08 13:01 ` [PATCH 07/16] loop: Push loop_ctl_mutex down into loop_clr_fd() Jan Kara
2018-11-08 13:01 ` [PATCH 08/16] loop: Push loop_ctl_mutex down to loop_get_status() Jan Kara
2018-11-08 13:01 ` [PATCH 09/16] loop: Push loop_ctl_mutex down to loop_set_status() Jan Kara
2018-11-08 13:01 ` [PATCH 10/16] loop: Push loop_ctl_mutex down to loop_set_fd() Jan Kara
2018-11-08 13:01 ` [PATCH 11/16] loop: Push loop_ctl_mutex down to loop_change_fd() Jan Kara
2018-11-08 13:01 ` [PATCH 12/16] loop: Move special partition reread handling in loop_clr_fd() Jan Kara
2018-11-08 13:01 ` [PATCH 13/16] loop: Move loop_reread_partitions() out of loop_ctl_mutex Jan Kara
2018-11-08 13:01 ` [PATCH 14/16] loop: Fix deadlock when calling blkdev_reread_part() Jan Kara
2018-11-08 13:01 ` [PATCH 15/16] loop: Avoid circular locking dependency between loop_ctl_mutex and bd_mutex Jan Kara
2018-11-08 13:01 ` [PATCH 16/16] loop: Get rid of 'nested' acquisition of loop_ctl_mutex Jan Kara
2018-11-08 13:21 ` [PATCH 0/16 v3] loop: Fix oops and possible deadlocks Jens Axboe
2018-11-08 13:25   ` Jan Kara
2018-11-08 13:31     ` Jens Axboe
2018-11-08 21:28 ` Theodore Y. Ts'o
2018-11-12 10:15   ` Jan Kara

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