[PATCH 4.20 110/111] loop: drop caches if offset or block_size are changed

[Greg Kroah-Hartman]

4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jaegeuk Kim <jaeg...@kernel.org>

commit 5db470e229e22b7eda6e23b5566e532c96fb5bc3 upstream.

If we don't drop caches used in old offset or block_size, we can get old data
from new offset/block_size, which gives unexpected data to user.

For example, Martijn found a loopback bug in the below scenario.
1) LOOP_SET_FD loads first two pages on loop file
2) LOOP_SET_STATUS64 changes the offset on the loop file
3) mount is failed due to the cached pages having wrong superblock

Cc: Jens Axboe <ax...@kernel.dk>
Cc: linux-bl...@vger.kernel.org
Reported-by: Martijn Coenen <m...@google.com>
Reviewed-by: Bart Van Assche <bvanass...@acm.org>
Signed-off-by: Jaegeuk Kim <jaeg...@kernel.org>
Signed-off-by: Jens Axboe <ax...@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/block/loop.c |   35 +++++++++++++++++++++++++++++++++--
 1 file changed, 33 insertions(+), 2 deletions(-)

--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1190,6 +1190,12 @@ loop_set_status(struct loop_device *lo,
                goto out_unlock;
        }
 
+       if (lo->lo_offset != info->lo_offset ||
+           lo->lo_sizelimit != info->lo_sizelimit) {
+               sync_blockdev(lo->lo_device);
+               kill_bdev(lo->lo_device);
+       }
+
        /* I/O need to be drained during transfer transition */
        blk_mq_freeze_queue(lo->lo_queue);
 
@@ -1218,6 +1224,14 @@ loop_set_status(struct loop_device *lo,
 
        if (lo->lo_offset != info->lo_offset ||
            lo->lo_sizelimit != info->lo_sizelimit) {
+               /* kill_bdev should have truncated all the pages */
+               if (lo->lo_device->bd_inode->i_mapping->nrpages) {
+                       err = -EAGAIN;
+                       pr_warn("%s: loop%d (%s) has still dirty pages 
(nrpages=%lu)\n",
+                               __func__, lo->lo_number, lo->lo_file_name,
+                               lo->lo_device->bd_inode->i_mapping->nrpages);
+                       goto out_unfreeze;
+               }
                if (figure_loop_size(lo, info->lo_offset, info->lo_sizelimit)) {
                        err = -EFBIG;
                        goto out_unfreeze;
@@ -1443,22 +1457,39 @@ static int loop_set_dio(struct loop_devi
 
 static int loop_set_block_size(struct loop_device *lo, unsigned long arg)
 {
+       int err = 0;
+
        if (lo->lo_state != Lo_bound)
                return -ENXIO;
 
        if (arg < 512 || arg > PAGE_SIZE || !is_power_of_2(arg))
                return -EINVAL;
 
+       if (lo->lo_queue->limits.logical_block_size != arg) {
+               sync_blockdev(lo->lo_device);
+               kill_bdev(lo->lo_device);
+       }
+
        blk_mq_freeze_queue(lo->lo_queue);
 
+       /* kill_bdev should have truncated all the pages */
+       if (lo->lo_queue->limits.logical_block_size != arg &&
+                       lo->lo_device->bd_inode->i_mapping->nrpages) {
+               err = -EAGAIN;
+               pr_warn("%s: loop%d (%s) has still dirty pages (nrpages=%lu)\n",
+                       __func__, lo->lo_number, lo->lo_file_name,
+                       lo->lo_device->bd_inode->i_mapping->nrpages);
+               goto out_unfreeze;
+       }
+
        blk_queue_logical_block_size(lo->lo_queue, arg);
        blk_queue_physical_block_size(lo->lo_queue, arg);
        blk_queue_io_min(lo->lo_queue, arg);
        loop_update_dio(lo);
-
+out_unfreeze:
        blk_mq_unfreeze_queue(lo->lo_queue);
 
-       return 0;
+       return err;
 }
 
 static int lo_simple_ioctl(struct loop_device *lo, unsigned int cmd,