linux-kernel - [PATCH AUTOSEL 4.9 45/45] ocfs2: fix potential use after free

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Date:   Wed,  5 Dec 2018 04:47:06 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     stable@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Pan Bian <bianpan2016@....com>, Mark Fasheh <mark@...heh.com>,
        Joel Becker <jlbec@...lplan.org>,
        Junxiao Bi <junxiao.bi@...cle.com>,
        Joseph Qi <jiangqi903@...il.com>,
        Changwei Ge <ge.changwei@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 4.9 45/45] ocfs2: fix potential use after free

From: Pan Bian <bianpan2016@....com>

[ Upstream commit 164f7e586739d07eb56af6f6d66acebb11f315c8 ]

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.  Move the put operation later.

Link: http://lkml.kernel.org/r/1543109237-110227-1-git-send-email-bianpan2016@163.com
Fixes: 781f200cb7a("ocfs2: Remove masklog ML_EXPORT.")
Signed-off-by: Pan Bian <bianpan2016@....com>
Reviewed-by: Andrew Morton <akpm@...ux-foundation.org>
Cc: Mark Fasheh <mark@...heh.com>
Cc: Joel Becker <jlbec@...lplan.org>
Cc: Junxiao Bi <junxiao.bi@...cle.com>
Cc: Joseph Qi <jiangqi903@...il.com>
Cc: Changwei Ge <ge.changwei@....com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 827fc9809bc2..3494e220b510 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;
 	}
-- 
2.17.1