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List:       linux-mm-commits
Subject:    [patch 31/31] ocfs2: fix potential use after free
From:       akpm () linux-foundation ! org
Date:       2018-11-30 22:10:54
Message-ID: 20181130221054.szxve%akpm () linux-foundation ! org
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From: Pan Bian <bianpan2016@163.com>
Subject: ocfs2: fix potential use after free

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@163.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Joseph Qi <jiangqi903@gmail.com>
Cc: Changwei Ge <ge.changwei@h3c.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/ocfs2/export.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/ocfs2/export.c~ocfs2-fix-potential-use-after-free
+++ a/fs/ocfs2/export.c
@@ -125,10 +125,10 @@ check_err:
 
 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;
 	}
_
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