From db5a93a43fea2aa3c3bbaf8c48d238e60d834676 Mon Sep 17 00:00:00 2001
From: Manuel Bentele
Date: Mon, 9 Nov 2020 07:16:07 +0100
Subject: [KERNEL] protect access to server list if alt server is added/removed

This patch locks the protecting spinlock of the DNBD3 device's new
server list. Otherwise a race condition between ioctl ADD_SRV/REM_SRV
(process context) and dnbd3 discover thread would be possible.
---
 src/kernel/blk.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/kernel/blk.c b/src/kernel/blk.c
index afdeea8..7e043c0 100644
--- a/src/kernel/blk.c
+++ b/src/kernel/blk.c
@@ -39,6 +39,7 @@ static int dnbd3_blk_ioctl(struct block_device *bdev, fmode_t mode, unsigned int
 	struct request_queue *blk_queue = dev->disk->queue;
 	char *imgname = NULL;
 	dnbd3_ioctl_t *msg = NULL;
+	unsigned long irqflags;
 	int i = 0;
 
 	while (dev->disconnecting) { /* do nothing */ }
@@ -193,9 +194,11 @@ static int dnbd3_blk_ioctl(struct block_device *bdev, fmode_t mode, unsigned int
 		}
 		else
 		{
+			spin_lock_irqsave(&dev->blk_lock, irqflags);
 			memcpy(&dev->new_servers[dev->new_servers_num].host, &msg->hosts[0], sizeof(msg->hosts[0]));
 			dev->new_servers[dev->new_servers_num].failures = (cmd == IOCTL_ADD_SRV ? 0 : 1); // 0 = ADD, 1 = REM
 			++dev->new_servers_num;
+			spin_unlock_irqrestore(&dev->blk_lock, irqflags);
 			result = 0;
 		}
 		break;
-- 
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