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

commit 310ca162d779efee8a2dc3731439680f3e9c1e86 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 15157a3eabb4bf45c85c6fde1b6e496ad8d0794b..a467dc43c389c9d29c3667787fea814468c7f579 100644 (file)
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -81,6 +81,7 @@
 
 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;
@@ -1012,7 +1013,7 @@ static int loop_clr_fd(struct loop_device *lo)
         */
        if (lo->lo_refcnt > 1) {
                lo->lo_flags |= LO_FLAGS_AUTOCLEAR;
-               mutex_unlock(&lo->lo_ctl_mutex);
+               mutex_unlock(&loop_ctl_mutex);
                return 0;
        }
 
@@ -1061,12 +1062,12 @@ static int loop_clr_fd(struct loop_device *lo)
        lo->lo_flags = 0;
        if (!part_shift)
                lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;
-       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;
@@ -1300,7 +1301,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
        struct loop_device *lo = bdev->bd_disk->private_data;
        int err;
 
-       mutex_lock_nested(&lo->lo_ctl_mutex, 1);
+       mutex_lock_nested(&loop_ctl_mutex, 1);
        switch (cmd) {
        case LOOP_SET_FD:
                err = loop_set_fd(lo, mode, bdev, arg);
@@ -1309,7 +1310,7 @@ 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;
@@ -1340,7 +1341,7 @@ 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;
@@ -1473,16 +1474,16 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode,
 
        switch(cmd) {
        case LOOP_SET_STATUS:
-               mutex_lock(&lo->lo_ctl_mutex);
+               mutex_lock(&loop_ctl_mutex);
                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:
-               mutex_lock(&lo->lo_ctl_mutex);
+               mutex_lock(&loop_ctl_mutex);
                err = loop_get_status_compat(
                        lo, (struct compat_loop_info __user *) arg);
-               mutex_unlock(&lo->lo_ctl_mutex);
+               mutex_unlock(&loop_ctl_mutex);
                break;
        case LOOP_SET_CAPACITY:
        case LOOP_CLR_FD:
@@ -1513,9 +1514,9 @@ static int lo_open(struct block_device *bdev, fmode_t mode)
                goto out;
        }
 
-       mutex_lock(&lo->lo_ctl_mutex);
+       mutex_lock(&loop_ctl_mutex);
        lo->lo_refcnt++;
-       mutex_unlock(&lo->lo_ctl_mutex);
+       mutex_unlock(&loop_ctl_mutex);
 out:
        mutex_unlock(&loop_index_mutex);
        return err;
@@ -1525,7 +1526,7 @@ static void __lo_release(struct loop_device *lo)
 {
        int err;
 
-       mutex_lock(&lo->lo_ctl_mutex);
+       mutex_lock(&loop_ctl_mutex);
 
        if (--lo->lo_refcnt)
                goto out;
@@ -1547,7 +1548,7 @@ static void __lo_release(struct loop_device *lo)
        }
 
 out:
-       mutex_unlock(&lo->lo_ctl_mutex);
+       mutex_unlock(&loop_ctl_mutex);
 }
 
 static void lo_release(struct gendisk *disk, fmode_t mode)
@@ -1593,10 +1594,10 @@ 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;
 }
 
@@ -1677,7 +1678,7 @@ 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);
+       mutex_init(&loop_ctl_mutex);
        lo->lo_number           = i;
        lo->lo_thread           = NULL;
        init_waitqueue_head(&lo->lo_event);
@@ -1789,19 +1790,19 @@ static long loop_control_ioctl(struct file *file, unsigned int cmd,
                ret = loop_lookup(&lo, parm);
                if (ret < 0)
                        break;
-               mutex_lock(&lo->lo_ctl_mutex);
+               mutex_lock(&loop_ctl_mutex);
                if (lo->lo_state != Lo_unbound) {
                        ret = -EBUSY;
-                       mutex_unlock(&lo->lo_ctl_mutex);
+                       mutex_unlock(&loop_ctl_mutex);
                        break;
                }
                if (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 fb113dd45e9766e61b62b1e5c5c3df076580ac1d..205dfb4767a0ac1e33ff606d675a14bd5f9b667c 100644 (file)
--- a/drivers/block/loop.h
+++ b/drivers/block/loop.h
@@ -55,7 +55,6 @@ struct loop_device {
        struct bio_list         lo_bio_list;
        unsigned int            lo_bio_count;
        int                     lo_state;
-       struct mutex            lo_ctl_mutex;
        struct task_struct      *lo_thread;
        wait_queue_head_t       lo_event;
        /* wait queue for incoming requests */