[PATCH 4.4 116/117] zram: dont call idr_remove() from zram_remove()

[Greg Kroah-Hartman]

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

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

From: Jerome Marchand <jmarchan@xxxxxxxxxx>

commit 17ec4cd985780a7e30aa45bb8f272237c12502a4 upstream.

The use of idr_remove() is forbidden in the callback functions of
idr_for_each().  It is therefore unsafe to call idr_remove in
zram_remove().

This patch moves the call to idr_remove() from zram_remove() to
hot_remove_store().  In the detroy_devices() path, idrs are removed by
idr_destroy().  This solves an use-after-free detected by KASan.

[akpm@xxxxxxxxxxxxxxxxxxxx: fix coding stype, per Sergey]
Signed-off-by: Jerome Marchand <jmarchan@xxxxxxxxxx>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/block/zram/zram_drv.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1325,7 +1325,6 @@ static int zram_remove(struct zram *zram
 
 	pr_info("Removed device: %s\n", zram->disk->disk_name);
 
-	idr_remove(&zram_index_idr, zram->disk->first_minor);
 	blk_cleanup_queue(zram->disk->queue);
 	del_gendisk(zram->disk);
 	put_disk(zram->disk);
@@ -1367,10 +1366,12 @@ static ssize_t hot_remove_store(struct c
 	mutex_lock(&zram_index_mutex);
 
 	zram = idr_find(&zram_index_idr, dev_id);
-	if (zram)
+	if (zram) {
 		ret = zram_remove(zram);
-	else
+		idr_remove(&zram_index_idr, dev_id);
+	} else {
 		ret = -ENODEV;
+	}
 
 	mutex_unlock(&zram_index_mutex);
 	return ret ? ret : count;