linux-kernel - [PATCH] ocfs2: fix potential use after free

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Date:   Sun, 25 Nov 2018 09:27:17 +0800
From:   Pan Bian <bianpan2016@....com>
To:     Mark Fasheh <mark@...heh.com>, Joel Becker <jlbec@...lplan.org>
Cc:     ocfs2-devel@....oracle.com, linux-kernel@...r.kernel.org,
        Tao Ma <boyu.mt@...bao.com>, Pan Bian <bianpan2016@....com>
Subject: [PATCH] ocfs2: fix potential use after free

The function ocfs2_get_dentry calls iput(inode) to drop the reference
count of inode, and if the reference count hits 0, inode is freed.
However, in this function, it then reads inode->i_generation, which may
result in a use after free bug. This patch moves the put operation
later.

Fixes: 781f200cb7a("ocfs2: Remove masklog ML_EXPORT.")
Signed-off-by: Pan Bian <bianpan2016@....com>
---
 fs/ocfs2/export.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ocfs2/export.c b/fs/ocfs2/export.c
index 9f88188..4bf8d58 100644
--- a/fs/ocfs2/export.c
+++ b/fs/ocfs2/export.c
@@ -125,10 +125,10 @@ static struct dentry *ocfs2_get_dentry(struct super_block *sb,
 
 check_gen:
 	if (handle->ih_generation != inode->i_generation) {
-		iput(inode);
 		trace_ocfs2_get_dentry_generation((unsigned long long)blkno,
 						  handle->ih_generation,
 						  inode->i_generation);
+		iput(inode);
 		result = ERR_PTR(-ESTALE);
 		goto bail;
 	}
-- 
2.7.4