Re: [PATCH v3 4/6] dm: fix dm_blk_report_zones

[Benjamin Marzinski <bmarzins@redhat.com>]

On Wed, Apr 09, 2025 at 03:02:58PM +0900, Damien Le Moal wrote:
> On 4/9/25 8:51 AM, Benjamin Marzinski wrote:
> > If dm_get_live_table() returned NULL, dm_put_live_table() was never
> > called. Also, it is possible that md->zone_revalidate_map will change
> > while calling this function. Only read it once, so that we are always
> > using the same value. Otherwise we might miss a call to
> > dm_put_live_table().
> > 
> > Finally, while md->zone_revalidate_map is set and a process is calling
> > blk_revalidate_disk_zones() to set up the zone append emulation
> > resources, it is possible that another process, perhaps triggered by
> > blkdev_report_zones_ioctl(), will call dm_blk_report_zones(). If
> > blk_revalidate_disk_zones() fails, these resources can be freed while
> > the other process is still using them, causing a use-after-free error.
> > 
> > blk_revalidate_disk_zones() will only ever be called when initially
> > setting up the zone append emulation resources, such as when setting up
> > a zoned dm-crypt table for the first time. Further table swaps will not
> > set md->zone_revalidate_map or call blk_revalidate_disk_zones().
> > However it must be called using the new table (referenced by
> > md->zone_revalidate_map) and the new queue limits while the DM device is
> > suspended. dm_blk_report_zones() needs some way to distinguish between a
> > call from blk_revalidate_disk_zones(), which must be allowed to use
> > md->zone_revalidate_map to access this not yet activated table, and all
> > other calls to dm_blk_report_zones(), which should not be allowed while
> > the device is suspended and cannot use md->zone_revalidate_map, since
> > the zone resources might be freed by the process currently calling
> > blk_revalidate_disk_zones().
> > 
> > Solve this by tracking the process that set md->zone_revalidate_map
> > dm_revalidate_zones() and only allowing that process to make use of it
> > in dm_blk_report_zones().
> 
> ..that sets md->zone_revalidate_map in dm_revalidate_zones() and... ?

Yep. I'll fix that.

> > 
> > Fixes: f211268ed1f9b ("dm: Use the block layer zone append emulation")
> > Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
> 
> I do not recall reviewing this version, but looks OK to me with the sentence
> above fixed.

The code is the same as the original version that you reviewed, but I
forgot to remove your Reviewed-by when I rewrote the commit message.
Sorry.

-Ben

> 
> > Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
> 
> 
> -- 
> Damien Le Moal
> Western Digital Research