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Message-ID: <Y9f4eAhcJXhh0+c2@debian>
Date: Mon, 30 Jan 2023 18:03:52 +0100
From: Guillaume Nault <gnault@...hat.com>
To: Shigeru Yoshida <syoshida@...hat.com>
Cc: jchapman@...alix.com, davem@...emloft.net, edumazet@...gle.com,
kuba@...nel.org, pabeni@...hat.com, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] l2tp: Avoid possible recursive deadlock in
l2tp_tunnel_register()
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 <syoshida@...hat.com>
> ---
> 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.
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