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[2a01:cb05:8918:ce00:9322:c8fd:d95c:b32b]) by smtp.gmail.com with ESMTPSA id x15-20020ac8018f000000b003b9a573aec6sm92722qtf.70.2023.01.30.09.03.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 30 Jan 2023 09:03:56 -0800 (PST) Date: Mon, 30 Jan 2023 18:03:52 +0100 From: Guillaume Nault To: Shigeru Yoshida Cc: jchapman@katalix.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] l2tp: Avoid possible recursive deadlock in l2tp_tunnel_register() Message-ID: References: <20230130154438.1373750-1-syoshida@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230130154438.1373750-1-syoshida@redhat.com> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, Jan 31, 2023 at 12:44:38AM +0900, Shigeru Yoshida wrote: > This patch fixes the issue by returning error when a pppol2tp socket > itself is passed. Fixes: 0b2c59720e65 ("l2tp: close all race conditions in l2tp_tunnel_register()") > Signed-off-by: Shigeru Yoshida > --- > net/l2tp/l2tp_ppp.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c > index db2e584c625e..88d1a339500b 100644 > --- a/net/l2tp/l2tp_ppp.c > +++ b/net/l2tp/l2tp_ppp.c > @@ -702,11 +702,14 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr, > struct l2tp_tunnel_cfg tcfg = { > .encap = L2TP_ENCAPTYPE_UDP, > }; > + int dummy = 0; There's no need to initialise dummy here. This is just confusing. We could even do without any extra variable and reuse error in sockfd_lookup(). > /* Prevent l2tp_tunnel_register() from trying to set up > - * a kernel socket. > + * a kernel socket. Also, prevent l2tp_tunnel_register() > + * from trying to use pppol2tp socket itself. > */ > - if (info.fd < 0) { > + if (info.fd < 0 || > + sock == sockfd_lookup(info.fd, &dummy)) { > error = -EBADF; > goto end; > } That should work, but the real problem is calling l2tp_tunnel_register() under lock_sock(). We should instead get/create the tunnel before locking the pppol2tp socket.