linux-kernel - [PATCH] vfs: check i_count under lock in evict

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Date:	Mon, 11 Jul 2016 17:15:04 -0700
From:	Chunwei Chen <david.chen@...exus.com>
To:	linux-kernel@...r.kernel.org
Cc:	Chunwei Chen <david.chen@...exus.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, stable@...r.kernel.org
Subject: [PATCH] vfs: check i_count under lock in evict_inodes

We need to check i_count again with i_lock held, because iput might re-add
i_count when lazytime is on. Without this check, we could end up with
double-free or use-after-free.

Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: linux-fsdevel@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Cc: stable@...r.kernel.org
Signed-off-by: Chunwei Chen <david.chen@...exus.com>
---
 fs/inode.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/inode.c b/fs/inode.c
index 4ccbc21..10bb020 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -607,7 +607,12 @@ again:
 			continue;
 
 		spin_lock(&inode->i_lock);
-		if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
+		/*
+		 * check i_count again with lock, because iput might re-add
+		 * it when lazytime is on.
+		 */
+		if (atomic_read(&inode->i_count) ||
+		    (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE))) {
 			spin_unlock(&inode->i_lock);
 			continue;
 		}
-- 
2.7.4