linux-kernel - [PATCH] fs:super:get_anon_bdev: fix race condition could cause dev exceed its upper limitation

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Message-ID: <20150623105445.GA6746@udknight.ahead-top.com>
Date:	Tue, 23 Jun 2015 18:54:45 +0800
From:	Wang YanQing <udknight@...il.com>
To:	viro@...iv.linux.org.uk
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] fs:super:get_anon_bdev: fix race condition could cause dev
 exceed its upper limitation

Execution of get_anon_bdev concurrently and preemptive kernel all
could bring race condition, it isn't enough to check dev against
its upper limitation with equality operator only.

This patch fix it.

Signed-off-by: Wang YanQing <udknight@...il.com>
---
 fs/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/super.c b/fs/super.c
index 928c20f..b613723 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -842,7 +842,7 @@ int get_anon_bdev(dev_t *p)
 	else if (error)
 		return -EAGAIN;
 
-	if (dev == (1 << MINORBITS)) {
+	if (dev >= (1 << MINORBITS)) {
 		spin_lock(&unnamed_dev_lock);
 		ida_remove(&unnamed_dev_ida, dev);
 		if (unnamed_dev_start > dev)
-- 
1.8.5.6.2.g3d8a54e.dirty
--
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