linux-kernel - [PATCH 4.20 38/80] CIFS: fix use-after-free of the lease keys

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Date:   Mon,  4 Feb 2019 11:36:58 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Aurelien Aptel <aaptel@...e.com>,
        Steve French <stfrench@...rosoft.com>,
        Paulo Alcantara <palcantara@...e.de>
Subject: [PATCH 4.20 38/80] CIFS: fix use-after-free of the lease keys

4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Aurelien Aptel <aaptel@...e.com>

commit d339adc12a4f885b572c5412e4869af8939db854 upstream.

The request buffers are freed right before copying the pointers.
Use the func args instead which are identical and still valid.

Simple reproducer (requires KASAN enabled) on a cifs mount:

echo foo > foo ; tail -f foo & rm foo

Cc: <stable@...r.kernel.org> # 4.20
Fixes: 179e44d49c2f ("smb3: add tracepoint for sending lease break responses to server")
Signed-off-by: Aurelien Aptel <aaptel@...e.com>
Signed-off-by: Steve French <stfrench@...rosoft.com>
Reviewed-by: Paulo Alcantara <palcantara@...e.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/cifs/smb2pdu.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -4339,8 +4339,8 @@ SMB2_lease_break(const unsigned int xid,
 	rc = cifs_send_recv(xid, ses, &rqst, &resp_buf_type, flags, &rsp_iov);
 	cifs_small_buf_release(req);
 
-	please_key_low = (__u64 *)req->LeaseKey;
-	please_key_high = (__u64 *)(req->LeaseKey+8);
+	please_key_low = (__u64 *)lease_key;
+	please_key_high = (__u64 *)(lease_key+8);
 	if (rc) {
 		cifs_stats_fail_inc(tcon, SMB2_OPLOCK_BREAK_HE);
 		trace_smb3_lease_err(le32_to_cpu(lease_state), tcon->tid,