[4.2.y-ckt stable] Patch "zram: don't call idr_remove() from zram_remove()" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    zram: don't call idr_remove() from zram_remove()

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt3.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 133c5bd195d264f990bd03b5c38de68481c3d3d3 Mon Sep 17 00:00:00 2001
From: Jerome Marchand <jmarchan at redhat.com>
Date: Fri, 15 Jan 2016 16:54:48 -0800
Subject: zram: don't call idr_remove() from zram_remove()

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 at linux-foundation.org: fix coding stype, per Sergey]
Signed-off-by: Jerome Marchand <jmarchan at redhat.com>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky at gmail.com>
Cc: Minchan Kim <minchan at kernel.org>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/block/zram/zram_drv.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 763301c..6a706f5 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1319,7 +1319,6 @@ 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);
@@ -1361,10 +1360,12 @@ static ssize_t hot_remove_store(struct class *class,
 	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;
--
1.9.1