linux-kernel - [PATCH 5.4 051/178] cifs: Fix cached_fid refcnt leak in open

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Message-Id: <20200629152523.2494198-52-sashal@kernel.org>
Date:   Mon, 29 Jun 2020 11:23:16 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Xiyu Yang <xiyuyang19@...an.edu.cn>,
        Xin Tan <tanxin.ctf@...il.com>,
        Steve French <stfrench@...rosoft.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [PATCH 5.4 051/178] cifs: Fix cached_fid refcnt leak in open_shroot

From: Xiyu Yang <xiyuyang19@...an.edu.cn>

commit 77577de64167aa0643d47ffbaacf3642632b321b upstream.

open_shroot() invokes kref_get(), which increases the refcount of the
"tcon->crfid" object. When open_shroot() returns not zero, it means the
open operation failed and close_shroot() will not be called to decrement
the refcount of the "tcon->crfid".

The reference counting issue happens in one normal path of
open_shroot(). When the cached root have been opened successfully in a
concurrent process, the function increases the refcount and jump to
"oshr_free" to return. However the current return value "rc" may not
equal to 0, thus the increased refcount will not be balanced outside the
function, causing a refcnt leak.

Fix this issue by setting the value of "rc" to 0 before jumping to
"oshr_free" label.

Signed-off-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@...il.com>
Signed-off-by: Steve French <stfrench@...rosoft.com>
CC: Stable <stable@...r.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/cifs/smb2ops.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index 58915d882285c..f5e893ed48aaa 100644
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -736,6 +736,7 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
 			/* close extra handle outside of crit sec */
 			SMB2_close(xid, tcon, fid.persistent_fid, fid.volatile_fid);
 		}
+		rc = 0;
 		goto oshr_free;
 	}

-- 
2.25.1