CIFS: fix use-after-free of the lease keys

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@vger.kernel.org> # 4.20
Fixes: 179e44d49c2f ("smb3: add tracepoint for sending lease break responses to server")
Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Paulo Alcantara <palcantara@suse.de>

diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index ef52d66424314f85ea5de5689bd31202937b6709..77b3aaa39b35c0c6dc1c96c8bdf0542fa1bf98bc 100644 (file)
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -4441,8 +4441,8 @@ SMB2_lease_break(const unsigned int xid, struct cifs_tcon *tcon,
        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,