From: Manjunath Patil <manjunath.b.patil@oracle.com>
Date: Tue, 30 Oct 2018 09:49:21 -0700
Subject: [PATCH] xen-blkfront: fix kernel panic with negotiate_mq error path
Git-commit: 6cc4a0863c9709c512280c64e698d68443ac8053
Patch-mainline: v4.20-rc2
References: bsc#1104967,FATE#325924
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

info->nr_rings isn't adjusted in case of ENOMEM error from
negotiate_mq(). This leads to kernel panic in error path.

Typical call stack involving panic -
 #8 page_fault at ffffffff8175936f
    [exception RIP: blkif_free_ring+33]
    RIP: ffffffffa0149491  RSP: ffff8804f7673c08  RFLAGS: 00010292
 ...
 #9 blkif_free at ffffffffa0149aaa [xen_blkfront]
 #10 talk_to_blkback at ffffffffa014c8cd [xen_blkfront]
 #11 blkback_changed at ffffffffa014ea8b [xen_blkfront]
 #12 xenbus_otherend_changed at ffffffff81424670
 #13 backend_changed at ffffffff81426dc3
 #14 xenwatch_thread at ffffffff81422f29
 #15 kthread at ffffffff810abe6a
 #16 ret_from_fork at ffffffff81754078

Cc: stable@vger.kernel.org
Fixes: 7ed8ce1c5fc7 ("xen-blkfront: move negotiate_mq to cover all cases of new VBDs")
Signed-off-by: Manjunath Patil <manjunath.b.patil@oracle.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Hannes Reinecke <hare@suse.com>
---
 drivers/block/xen-blkfront.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 9eea83ae01c6..9ac3999a55b7 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -1919,6 +1919,7 @@ static int negotiate_mq(struct blkfront_info *info)
 	info->rinfo = kzalloc(sizeof(struct blkfront_ring_info) * info->nr_rings, GFP_KERNEL);
 	if (!info->rinfo) {
 		xenbus_dev_fatal(info->xbdev, -ENOMEM, "allocating ring_info structure");
+		info->nr_rings = 0;
 		return -ENOMEM;
 	}
 
-- 
2.16.4