dm: fix dm_blk_report_zones

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 sets md->zone_revalidate_map in
dm_revalidate_zones() and only allowing that process to make use of it
in dm_blk_report_zones().

Fixes: f211268 ("dm: Use the block layer zone append emulation")
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Tested-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

Author: bmarzins

drivers/md/dm-core.h

@@ -141,6 +141,7 @@ struct mapped_device {
 #ifdef CONFIG_BLK_DEV_ZONED
 	unsigned int nr_zones;
 	void *zone_revalidate_map;
+	struct task_struct *revalidate_map_task;
 #endif
 
 #ifdef CONFIG_IMA

drivers/md/dm-zone.c

@@ -56,24 +56,31 @@ int dm_blk_report_zones(struct gendisk *disk, sector_t sector,
 {
 	struct mapped_device *md = disk->private_data;
 	struct dm_table *map;
-	int srcu_idx, ret;
+	struct dm_table *zone_revalidate_map = md->zone_revalidate_map;
+	int srcu_idx, ret = -EIO;
+	bool put_table = false;
 
-	if (!md->zone_revalidate_map) {
-		/* Regular user context */
+	if (!zone_revalidate_map || md->revalidate_map_task != current) {
+		/*
+		 * Regular user context or
+		 * Zone revalidation during __bind() is in progress, but this
+		 * call is from a different process
+		 */
 		if (dm_suspended_md(md))
 			return -EAGAIN;
 
 		map = dm_get_live_table(md, &srcu_idx);
-		if (!map)
-			return -EIO;
+		put_table = true;
 	} else {
 		/* Zone revalidation during __bind() */
-		map = md->zone_revalidate_map;
+		map = zone_revalidate_map;
 	}
 
-	ret = dm_blk_do_report_zones(md, map, sector, nr_zones, cb, data);
+	if (map)
+		ret = dm_blk_do_report_zones(md, map, sector, nr_zones, cb,
+					     data);
 
-	if (!md->zone_revalidate_map)
+	if (put_table)
 		dm_put_live_table(md, srcu_idx);
 
 	return ret;
@@ -175,7 +182,9 @@ int dm_revalidate_zones(struct dm_table *t, struct request_queue *q)
 	 * our table for dm_blk_report_zones() to use directly.
 	 */
 	md->zone_revalidate_map = t;
+	md->revalidate_map_task = current;
 	ret = blk_revalidate_disk_zones(disk);
+	md->revalidate_map_task = NULL;
 	md->zone_revalidate_map = NULL;
 
 	if (ret) {