| Message ID | 1518430280-16671-2-git-send-email-jchapman@katalix.com |
|---|---|
| State | Changes Requested, archived |
| Delegated to: | David Miller |
| Headers | show |
| Series | l2tp: fix API races discovered by syzbot | expand |
From: James Chapman <jchapman@katalix.com> Date: Mon, 12 Feb 2018 10:11:05 +0000 > Since L2TP hooks on sockets opened by userspace using sk_user_data, we > may race with other socket families that attempt to use the same > socket. > > This problem was discovered by syzbot using AF_KCM. KCM has since been > modified to use only TCP sockets to avoid hitting this issue but we > should prevent such races in L2TP anyway. > > Fixes: c8fffcea0a079 ("l2tp: Refactor l2tp core driver to make use of the common UDP tunnel function") > Reported-by: syzbot+8865eaff7f9acd593945@syzkaller.appspotmail.com Yikes. Where is your signoff James? > Kernel BUG at net/l2tp/l2tp_ppp.c:176! > invalid opcode: 0000 [#1] SMP KASAN > Dumping ftrace buffer: > (ftrace buffer empty) And this oops dump should be before the various fixes/reported-by/signed-off-by tags. Thanks.
On Mon, Feb 12, 2018 at 10:11:05AM +0000, James Chapman wrote: > Since L2TP hooks on sockets opened by userspace using sk_user_data, we > may race with other socket families that attempt to use the same > socket. > > This problem was discovered by syzbot using AF_KCM. KCM has since been > modified to use only TCP sockets to avoid hitting this issue but we > should prevent such races in L2TP anyway. > > Fixes: c8fffcea0a079 ("l2tp: Refactor l2tp core driver to make use of the common UDP tunnel function") > Reported-by: syzbot+8865eaff7f9acd593945@syzkaller.appspotmail.com > > Kernel BUG at net/l2tp/l2tp_ppp.c:176! > invalid opcode: 0000 [#1] SMP KASAN > Dumping ftrace buffer: > (ftrace buffer empty) > Modules linked in: > CPU: 1 PID: 3503 Comm: syzkaller938388 Not tainted 4.15.0-rc7+ #181 > Hardware name: Google Google Compute Engine/Google Compute Engine > RIP: 0010:pppol2tp_sock_to_session net/l2tp/l2tp_ppp.c:176 [inline] > RIP: 0010:pppol2tp_sendmsg+0x512/0x670 net/l2tp/l2tp_ppp.c:304 > RSP: 0018:ffff8801d4887438 EFLAGS: 00010293 > RAX: ffff8801bfef2180 RBX: ffff8801bff88440 RCX: ffffffff84ffbca2 > RDX: 0000000000000000 RSI: ffff8801d4887598 RDI: ffff8801bff88820 > RBP: ffff8801d48874a8 R08: 0000000000000000 R09: 1ffff1003a910e17 > R10: 0000000000000003 R11: 0000000000000001 R12: ffff8801bfff9bc0 > R13: 0000000000000000 R14: 0000000000008000 R15: 0000000000000000 > FS: 0000000001194880(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000020ea0000 CR3: 00000001bfecf001 CR4: 00000000001606e0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Call Trace: > sock_sendmsg_nosec net/socket.c:628 [inline] > sock_sendmsg+0xca/0x110 net/socket.c:638 > kernel_sendmsg+0x47/0x60 net/socket.c:646 > sock_no_sendpage+0x1cc/0x280 net/core/sock.c:2581 > kernel_sendpage+0xbf/0xe0 net/socket.c:3349 > kcm_write_msgs+0x404/0x1b80 net/kcm/kcmsock.c:646 > kcm_sendmsg+0x148d/0x22d0 net/kcm/kcmsock.c:1035 > sock_sendmsg_nosec net/socket.c:628 [inline] > sock_sendmsg+0xca/0x110 net/socket.c:638 > ___sys_sendmsg+0x767/0x8b0 net/socket.c:2018 > __sys_sendmsg+0xe5/0x210 net/socket.c:2052 > SYSC_sendmsg net/socket.c:2063 [inline] > SyS_sendmsg+0x2d/0x50 net/socket.c:2059 > entry_SYSCALL_64_fastpath+0x23/0x9a > RIP: 0033:0x440159 > RSP: 002b:00007ffe74df8288 EFLAGS: 00000217 ORIG_RAX: 000000000000002e > RAX: ffffffffffffffda RBX: ffffffffffffffff RCX: 0000000000440159 > RDX: 0000000000000000 RSI: 00000000201fcfc8 RDI: 0000000000000005 > RBP: 00000000006ca018 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000217 R12: 0000000000401ac0 > R13: 0000000000401b50 R14: 0000000000000000 R15: 0000000000000000 > Code: c5 61 70 fc 48 8b 7d d0 e8 7c c2 5b fd 84 c0 74 0d e8 b3 61 70 fc 48 89 df e8 3b 49 2f ff 41 bd f7 ff ff ff eb 86 e8 9e 61 70 fc <0f> 0b 41 bd 95 ff ff ff e9 74 ff ff ff e8 ec 32 a8 fc e9 77 fb > RIP: pppol2tp_sock_to_session net/l2tp/l2tp_ppp.c:176 [inline] RSP: ffff8801d4887438 > RIP: pppol2tp_sendmsg+0x512/0x670 net/l2tp/l2tp_ppp.c:304 RSP: ffff8801d4887438 > --- > net/l2tp/l2tp_core.c | 21 ++++++++++++++++++--- > net/l2tp/l2tp_ppp.c | 8 ++++++-- > 2 files changed, 24 insertions(+), 5 deletions(-) > > diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c > index 194a7483bb93..de7dce64173f 100644 > --- a/net/l2tp/l2tp_core.c > +++ b/net/l2tp/l2tp_core.c > @@ -1216,6 +1216,7 @@ static void l2tp_tunnel_destruct(struct sock *sk) > > > /* Disable udp encapsulation */ > + write_lock_bh(&sk->sk_callback_lock); > switch (tunnel->encap) { > case L2TP_ENCAPTYPE_UDP: > /* No longer an encapsulation socket. See net/ipv4/udp.c */ > @@ -1229,7 +1230,8 @@ static void l2tp_tunnel_destruct(struct sock *sk) > > /* Remove hooks into tunnel socket */ > sk->sk_destruct = tunnel->old_sk_destruct; > - sk->sk_user_data = NULL; > + rcu_assign_sk_user_data(sk, NULL); > + write_unlock_bh(&sk->sk_callback_lock); > > /* Remove the tunnel struct from the tunnel list */ > pn = l2tp_pernet(tunnel->l2tp_net); > @@ -1583,6 +1585,20 @@ int l2tp_tunnel_create(struct net *net, int fd, int version, u32 tunnel_id, u32 > } > #endif > > + /* Assign socket sk_user_data. Must be done with > + * sk_callback_lock. Bail if sk_user_data is already assigned. > + */ > + write_lock_bh(&sk->sk_callback_lock); > + if (sk->sk_user_data) { > + err = -EALREADY; > + write_unlock_bh(&sk->sk_callback_lock); > + kfree(tunnel); > + tunnel = NULL; > + goto err; > + } > + rcu_assign_sk_user_data(sk, tunnel); > + write_unlock_bh(&sk->sk_callback_lock); > + I'd rather use this code only to replace the direct ->sk_user_data assignment (in the 'else' branch). It looks strange to assign it here using the new locking scheme and let setup_udp_tunnel_sock() re-assign it later, with the same value but without locking. Of course, if every user of ->sk_user_data was updated to the new locking scheme, that should kill the race without having to update setup_udp_tunnel_sock(). But only KCM locks ->sk_callback_lock for now and, as you pointed out, it doesn't act on UDP sockets anymore. Therefore setting ->sk_user_data here rather than at its original place only brings confusion in my opinion. And using rcu_assign_sk_user_data() is a bit confusing too. We never treat ->sk_user_data as RCU protected in the rest of the code. > /* Mark socket as an encapsulation socket. See net/ipv4/udp.c */ > tunnel->encap = encap; > if (encap == L2TP_ENCAPTYPE_UDP) { > @@ -1594,8 +1610,6 @@ int l2tp_tunnel_create(struct net *net, int fd, int version, u32 tunnel_id, u32 > udp_cfg.encap_destroy = l2tp_udp_encap_destroy; > > setup_udp_tunnel_sock(net, sock, &udp_cfg); > - } else { > - sk->sk_user_data = tunnel; > }
diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c index 194a7483bb93..de7dce64173f 100644 --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -1216,6 +1216,7 @@ static void l2tp_tunnel_destruct(struct sock *sk) /* Disable udp encapsulation */ + write_lock_bh(&sk->sk_callback_lock); switch (tunnel->encap) { case L2TP_ENCAPTYPE_UDP: /* No longer an encapsulation socket. See net/ipv4/udp.c */ @@ -1229,7 +1230,8 @@ static void l2tp_tunnel_destruct(struct sock *sk) /* Remove hooks into tunnel socket */ sk->sk_destruct = tunnel->old_sk_destruct; - sk->sk_user_data = NULL; + rcu_assign_sk_user_data(sk, NULL); + write_unlock_bh(&sk->sk_callback_lock); /* Remove the tunnel struct from the tunnel list */ pn = l2tp_pernet(tunnel->l2tp_net); @@ -1583,6 +1585,20 @@ int l2tp_tunnel_create(struct net *net, int fd, int version, u32 tunnel_id, u32 } #endif + /* Assign socket sk_user_data. Must be done with + * sk_callback_lock. Bail if sk_user_data is already assigned. + */ + write_lock_bh(&sk->sk_callback_lock); + if (sk->sk_user_data) { + err = -EALREADY; + write_unlock_bh(&sk->sk_callback_lock); + kfree(tunnel); + tunnel = NULL; + goto err; + } + rcu_assign_sk_user_data(sk, tunnel); + write_unlock_bh(&sk->sk_callback_lock); + /* Mark socket as an encapsulation socket. See net/ipv4/udp.c */ tunnel->encap = encap; if (encap == L2TP_ENCAPTYPE_UDP) { @@ -1594,8 +1610,6 @@ int l2tp_tunnel_create(struct net *net, int fd, int version, u32 tunnel_id, u32 udp_cfg.encap_destroy = l2tp_udp_encap_destroy; setup_udp_tunnel_sock(net, sock, &udp_cfg); - } else { - sk->sk_user_data = tunnel; } /* Hook on the tunnel socket destructor so that we can cleanup @@ -1603,6 +1617,7 @@ int l2tp_tunnel_create(struct net *net, int fd, int version, u32 tunnel_id, u32 */ tunnel->old_sk_destruct = sk->sk_destruct; sk->sk_destruct = &l2tp_tunnel_destruct; + tunnel->sock = sk; tunnel->fd = fd; lockdep_set_class_and_name(&sk->sk_lock.slock, &l2tp_socket_class, "l2tp_sock"); diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c index 59f246d7b290..fe5a0043dd32 100644 --- a/net/l2tp/l2tp_ppp.c +++ b/net/l2tp/l2tp_ppp.c @@ -443,7 +443,9 @@ static void pppol2tp_session_destruct(struct sock *sk) skb_queue_purge(&sk->sk_write_queue); if (session) { - sk->sk_user_data = NULL; + write_lock_bh(&sk->sk_callback_lock); + rcu_assign_sk_user_data(sk, NULL); + write_unlock_bh(&sk->sk_callback_lock); BUG_ON(session->magic != L2TP_SESSION_MAGIC); l2tp_session_dec_refcount(session); } @@ -796,7 +798,9 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr, out_no_ppp: /* This is how we get the session context from the socket. */ - sk->sk_user_data = session; + write_lock_bh(&sk->sk_callback_lock); + rcu_assign_sk_user_data(sk, session); + write_unlock_bh(&sk->sk_callback_lock); rcu_assign_pointer(ps->sk, sk); mutex_unlock(&ps->sk_lock);
Since L2TP hooks on sockets opened by userspace using sk_user_data, we may race with other socket families that attempt to use the same socket. This problem was discovered by syzbot using AF_KCM. KCM has since been modified to use only TCP sockets to avoid hitting this issue but we should prevent such races in L2TP anyway. Fixes: c8fffcea0a079 ("l2tp: Refactor l2tp core driver to make use of the common UDP tunnel function") Reported-by: syzbot+8865eaff7f9acd593945@syzkaller.appspotmail.com Kernel BUG at net/l2tp/l2tp_ppp.c:176! invalid opcode: 0000 [#1] SMP KASAN Dumping ftrace buffer: (ftrace buffer empty) Modules linked in: CPU: 1 PID: 3503 Comm: syzkaller938388 Not tainted 4.15.0-rc7+ #181 Hardware name: Google Google Compute Engine/Google Compute Engine RIP: 0010:pppol2tp_sock_to_session net/l2tp/l2tp_ppp.c:176 [inline] RIP: 0010:pppol2tp_sendmsg+0x512/0x670 net/l2tp/l2tp_ppp.c:304 RSP: 0018:ffff8801d4887438 EFLAGS: 00010293 RAX: ffff8801bfef2180 RBX: ffff8801bff88440 RCX: ffffffff84ffbca2 RDX: 0000000000000000 RSI: ffff8801d4887598 RDI: ffff8801bff88820 RBP: ffff8801d48874a8 R08: 0000000000000000 R09: 1ffff1003a910e17 R10: 0000000000000003 R11: 0000000000000001 R12: ffff8801bfff9bc0 R13: 0000000000000000 R14: 0000000000008000 R15: 0000000000000000 FS: 0000000001194880(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000020ea0000 CR3: 00000001bfecf001 CR4: 00000000001606e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: sock_sendmsg_nosec net/socket.c:628 [inline] sock_sendmsg+0xca/0x110 net/socket.c:638 kernel_sendmsg+0x47/0x60 net/socket.c:646 sock_no_sendpage+0x1cc/0x280 net/core/sock.c:2581 kernel_sendpage+0xbf/0xe0 net/socket.c:3349 kcm_write_msgs+0x404/0x1b80 net/kcm/kcmsock.c:646 kcm_sendmsg+0x148d/0x22d0 net/kcm/kcmsock.c:1035 sock_sendmsg_nosec net/socket.c:628 [inline] sock_sendmsg+0xca/0x110 net/socket.c:638 ___sys_sendmsg+0x767/0x8b0 net/socket.c:2018 __sys_sendmsg+0xe5/0x210 net/socket.c:2052 SYSC_sendmsg net/socket.c:2063 [inline] SyS_sendmsg+0x2d/0x50 net/socket.c:2059 entry_SYSCALL_64_fastpath+0x23/0x9a RIP: 0033:0x440159 RSP: 002b:00007ffe74df8288 EFLAGS: 00000217 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: ffffffffffffffff RCX: 0000000000440159 RDX: 0000000000000000 RSI: 00000000201fcfc8 RDI: 0000000000000005 RBP: 00000000006ca018 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000217 R12: 0000000000401ac0 R13: 0000000000401b50 R14: 0000000000000000 R15: 0000000000000000 Code: c5 61 70 fc 48 8b 7d d0 e8 7c c2 5b fd 84 c0 74 0d e8 b3 61 70 fc 48 89 df e8 3b 49 2f ff 41 bd f7 ff ff ff eb 86 e8 9e 61 70 fc <0f> 0b 41 bd 95 ff ff ff e9 74 ff ff ff e8 ec 32 a8 fc e9 77 fb RIP: pppol2tp_sock_to_session net/l2tp/l2tp_ppp.c:176 [inline] RSP: ffff8801d4887438 RIP: pppol2tp_sendmsg+0x512/0x670 net/l2tp/l2tp_ppp.c:304 RSP: ffff8801d4887438 --- net/l2tp/l2tp_core.c | 21 ++++++++++++++++++--- net/l2tp/l2tp_ppp.c | 8 ++++++-- 2 files changed, 24 insertions(+), 5 deletions(-)