3.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxx> Reported-by: syzbot <syzbot+bf89c128e05dd6c62523@xxxxxxxxxxxxxxxxxxxxxxxxx> Reviewed-by: Jan Kara <jack@xxxxxxx> Signed-off-by: Jan Kara <jack@xxxxxxx> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/block/loop.c | 47 ++++++++++++++++++++++++----------------------- drivers/block/loop.h | 1 - 2 files changed, 24 insertions(+), 24 deletions(-) --- 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_devic */ 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_devic 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 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 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 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_ 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 * 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_dev { 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_dev } 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 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 * 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 fi 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; --- 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 */
