block/loop: Use global lock for ioctl() operation.

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>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index a29ef169f360abcfa5ad7c395c27a69431a9d942..63008e87977181805639086abdc7efab0c28d73a 100644 (file)
--- 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 4d42c7af7de750e8f72e74bf0edb0b2ce26d2208..af75a5ee409440b24ab633d3a744ed9f8c307256 100644 (file)
--- 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;