* [PATCH] loop: drop caches if offset or block_size are changed
@ 2019-01-10 3:17 Jaegeuk Kim
2019-01-10 3:51 ` Jens Axboe
0 siblings, 1 reply; 4+ messages in thread
From: Jaegeuk Kim @ 2019-01-10 3:17 UTC (permalink / raw)
To: linux-kernel, linux-f2fs-devel; +Cc: jaegeuk, Jens Axboe, linux-block
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 <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org
Reported-by: Martijn Coenen <maco@google.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
---
drivers/block/loop.c | 35 +++++++++++++++++++++++++++++++++--
1 file changed, 33 insertions(+), 2 deletions(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index b8a0720d3653..cf5538942834 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1190,6 +1190,12 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
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, const struct loop_info64 *info)
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_device *lo, unsigned long arg)
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,
--
2.19.0.605.g01d371f741-goog
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] loop: drop caches if offset or block_size are changed
2019-01-10 3:17 [PATCH] loop: drop caches if offset or block_size are changed Jaegeuk Kim
@ 2019-01-10 3:51 ` Jens Axboe
2019-03-14 5:07 ` Gwendal Grignou
0 siblings, 1 reply; 4+ messages in thread
From: Jens Axboe @ 2019-01-10 3:51 UTC (permalink / raw)
To: Jaegeuk Kim, linux-kernel, linux-f2fs-devel; +Cc: linux-block
On 1/9/19 8:17 PM, Jaegeuk Kim wrote:
> 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
Applied, thanks.
--
Jens Axboe
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] loop: drop caches if offset or block_size are changed
2019-01-10 3:51 ` Jens Axboe
@ 2019-03-14 5:07 ` Gwendal Grignou
2019-04-15 21:13 ` grygorii tertychnyi
0 siblings, 1 reply; 4+ messages in thread
From: Gwendal Grignou @ 2019-03-14 5:07 UTC (permalink / raw)
To: axboe; +Cc: jaegeuk, linux-block, linux-f2fs-devel, linux-kernel
Jaegeuk,
We have observed an issue in production with this patch.
(ihttps://bugs.chromium.org/p/chromium/issues/detail?id=938958#c38)
If we mount -o loop,offset=... $file, mount will issue 2 ioctl back to back:
- LOOP_SET_FD
- LOOP_SET_STATUS64 with offset change.
Looking at kill_bdev, it calls truncate_inode_pages(). From its
comment, mapping->nrpages can still be non-zero:
"""
* Note: When this function returns, there can be a page in the process of
* deletion (inside __delete_from_page_cache()) in the specified range. Thus
* mapping->nrpages can be non-zero when this function returns even after
* truncation of the whole mapping.
"""
It is therefore possible to have truncated all the pages, but nr_page
still be !0.
We would fail the mount with -EAGAIN while it was perfectly valid.
Is the test for nrpages really necessary in the second part of the patch?
Gwendal.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH] loop: drop caches if offset or block_size are changed
2019-03-14 5:07 ` Gwendal Grignou
@ 2019-04-15 21:13 ` grygorii tertychnyi
0 siblings, 0 replies; 4+ messages in thread
From: grygorii tertychnyi @ 2019-04-15 21:13 UTC (permalink / raw)
To: jaegeuk, gwendal
Cc: xe-linux-external, axboe, linux-block, linux-f2fs-devel, linux-kernel
Jaegeuk,
We also observed an issue with this patch.
After heavely working with image.bin (haxdump with different offsets)
next mount call fails:
# mount -o ro,loop,offset=45967633 -t squashfs image.bin /tmp/gi45
mount: image.bin: failed to setup loop device: Resource temporarily unavailable
# dmesg | tail -n1
loop_set_status: loop2 () has still dirty pages (nrpages=1)
-- Grygorii
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2019-04-15 21:20 UTC | newest]
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2019-01-10 3:17 [PATCH] loop: drop caches if offset or block_size are changed Jaegeuk Kim
2019-01-10 3:51 ` Jens Axboe
2019-03-14 5:07 ` Gwendal Grignou
2019-04-15 21:13 ` grygorii tertychnyi
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