Re: md/dm-mpath: check whether all pgpaths have same uuid in multipath_ctr()

[Mike Snitzer <snitzer@redhat.com>]

On Wed, Mar 24 2021 at  9:21pm -0400,
Zhiqiang Liu <liuzhiqiang26@huawei.com> wrote:

> 
> 
> On 2021/3/22 22:22, Mike Snitzer wrote:
> > On Mon, Mar 22 2021 at  4:11am -0400,
> > Christoph Hellwig <hch@infradead.org> wrote:
> > 
> >> On Sat, Mar 20, 2021 at 03:19:23PM +0800, Zhiqiang Liu wrote:
> >>> From: Zhiqiang Liu <liuzhiqiang26@huawei.com>
> >>>
> >>> When we make IO stress test on multipath device, there will
> >>> be a metadata err because of wrong path. In the test, we
> >>> concurrent execute 'iscsi device login|logout' and
> >>> 'multipath -r' command with IO stress on multipath device.
> >>> In some case, systemd-udevd may have not time to process
> >>> uevents of iscsi device logout|login, and then 'multipath -r'
> >>> command triggers multipathd daemon calls ioctl to load table
> >>> with incorrect old device info from systemd-udevd.
> >>> Then, one iscsi path may be incorrectly attached to another
> >>> multipath which has different uuid. Finally, the metadata err
> >>> occurs when umounting filesystem to down write metadata on
> >>> the iscsi device which is actually not owned by the multipath
> >>> device.
> >>>
> >>> So we need to check whether all pgpaths of one multipath have
> >>> the same uuid, if not, we should throw a error.
> >>>
> >>> Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
> >>> Signed-off-by: lixiaokeng <lixiaokeng@huawei.com>
> >>> Signed-off-by: linfeilong <linfeilong@huawei.com>
> >>> Signed-off-by: Wubo <wubo40@huawei.com>
> >>> ---
> >>>  drivers/md/dm-mpath.c   | 52 +++++++++++++++++++++++++++++++++++++++++
> >>>  drivers/scsi/scsi_lib.c |  1 +
> >>>  2 files changed, 53 insertions(+)
> >>>
> >>> diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
> >>> index bced42f082b0..f0b995784b53 100644
> >>> --- a/drivers/md/dm-mpath.c
> >>> +++ b/drivers/md/dm-mpath.c
> >>> @@ -24,6 +24,7 @@
> >>>  #include <linux/workqueue.h>
> >>>  #include <linux/delay.h>
> >>>  #include <scsi/scsi_dh.h>
> >>> +#include <linux/dm-ioctl.h>
> >>>  #include <linux/atomic.h>
> >>>  #include <linux/blk-mq.h>
> >>>
> >>> @@ -1169,6 +1170,45 @@ static int parse_features(struct dm_arg_set *as, struct multipath *m)
> >>>  	return r;
> >>>  }
> >>>
> >>> +#define SCSI_VPD_LUN_ID_PREFIX_LEN 4
> >>> +#define MPATH_UUID_PREFIX_LEN 7
> >>> +static int check_pg_uuid(struct priority_group *pg, char *md_uuid)
> >>> +{
> >>> +	char pgpath_uuid[DM_UUID_LEN] = {0};
> >>> +	struct request_queue *q;
> >>> +	struct pgpath *pgpath;
> >>> +	struct scsi_device *sdev;
> >>> +	ssize_t count;
> >>> +	int r = 0;
> >>> +
> >>> +	list_for_each_entry(pgpath, &pg->pgpaths, list) {
> >>> +		q = bdev_get_queue(pgpath->path.dev->bdev);
> >>> +		sdev = scsi_device_from_queue(q);
> >>
> >> Common dm-multipath code should never poke into scsi internals.  This
> >> is something for the device handler to check.  It probably also won't
> >> work for all older devices.
> > 
> > Definitely.
> > 
> > But that aside, userspace (multipathd) _should_ be able to do extra
> > validation, _before_ pushing down a new table to the kernel, rather than
> > forcing the kernel to do it.
> 
> As your said, it is better to do extra validation in userspace (multipathd).
> However, in some cases, the userspace cannot see the real-time present devices
> info as Martin (committer of multipath-tools) said.
> In addition, the kernel can see right device info in the table at any time,
> so the uuid check in kernel can ensure one multipath is composed with paths mapped to
> the same device.
> 
> Considering the severity of the wrong path in multipath, I think it worths more
> checking.

As already said: this should be fixable in userspace.  Please work with
multipath-tools developers to address this.

Mike