[PATCH] vfs: check i_count under lock in evict_inodes

[Chunwei Chen]

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@xxxxxxxxxxxxxxxxxx>
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Chunwei Chen <david.chen@xxxxxxxxxxx>
---
 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