From 362b6725778bd3eb7a73e36a75e92e2b09ec7541 Mon Sep 17 00:00:00 2001 From: James Chapman Date: Mon, 29 Jul 2024 09:49:07 +0100 Subject: [PATCH] l2tp: fix tunnel init / UDP socket receive race syzbot exposes a race during tunnel init when the tunnel's UDP socket is made ready to receive traffic before the tunnel's l2tp_net pointer is set. This can result in a segfault in net_generic() when l2tp_tunnel_get tries to access its per-net list. Unable to handle kernel paging request at virtual address dfff800000000257 KASAN: probably user-memory-access in range [0x00000000000012b8-0x00000000000012bf] Mem abort info: ESR = 0x0000000096000005 EC = 0x25: DABT (current EL), IL = 32 bits SET = 0, FnV = 0 EA = 0, S1PTW = 0 FSC = 0x05: level 1 translation fault Data abort info: ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000 CM = 0, WnR = 0, TnD = 0, TagAccess = 0 GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0 [dfff800000000257] address between user and kernel address ranges Internal error: Oops: 0000000096000005 [#1] PREEMPT SMP Modules linked in: CPU: 1 PID: 6969 Comm: syz.2.105 Not tainted 6.10.0-rc7-syzkaller-gc912bf709078 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024 pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : net_generic+0xd0/0x250 include/net/netns/generic.h:46 lr : rcu_read_lock include/linux/rcupdate.h:782 [inline] lr : net_generic+0x54/0x250 include/net/netns/generic.h:45 sp : ffff8000a6c86c10 x29: ffff8000a6c86c10 x28: dfff800000000000 x27: 0000000000000802 x26: 0000000000000002 x25: 1ffff00014d90d88 x24: dfff800000000000 x23: ffff0000ca3fbd70 x22: ffff8000a6c86c40 x21: dfff800000000000 x20: 00000000000012b8 x19: 000000000000004e x18: 1ffff00014d90cfe x17: 000000000003099a x16: ffff80008054bde8 x15: 0000000000000001 x14: ffff80008f100568 x13: dfff800000000000 x12: 00000000af8628cd x11: 0000000068a0e22d x10: 0000000000ff0100 x9 : 0000000000000000 x8 : 0000000000000257 x7 : ffff80008a4326a8 x6 : 0000000000000000 x5 : 0000000000000000 x4 : 0000000000000000 x3 : 0000000000000002 x2 : 0000000000000008 x1 : ffff80008b681f20 x0 : 0000000000000001 Call trace: net_generic+0xd0/0x250 include/net/netns/generic.h:46 l2tp_pernet net/l2tp/l2tp_core.c:125 [inline] l2tp_tunnel_get+0x90/0x464 net/l2tp/l2tp_core.c:207 l2tp_udp_recv_core net/l2tp/l2tp_core.c:852 [inline] l2tp_udp_encap_recv+0x314/0xb3c net/l2tp/l2tp_core.c:933 udpv6_queue_rcv_one_skb+0x1870/0x1ad4 net/ipv6/udp.c:727 udpv6_queue_rcv_skb+0x3bc/0x574 net/ipv6/udp.c:789 udp6_unicast_rcv_skb+0x1cc/0x320 net/ipv6/udp.c:929 __udp6_lib_rcv+0xbcc/0x1330 net/ipv6/udp.c:1018 udpv6_rcv+0x88/0x9c net/ipv6/udp.c:1133 ip6_protocol_deliver_rcu+0x988/0x12a4 net/ipv6/ip6_input.c:438 ip6_input_finish+0x164/0x298 net/ipv6/ip6_input.c:483 NF_HOOK+0x328/0x3d4 include/linux/netfilter.h:314 ip6_input+0x90/0xa8 net/ipv6/ip6_input.c:492 dst_input include/net/dst.h:460 [inline] ip6_rcv_finish+0x1f0/0x21c net/ipv6/ip6_input.c:79 NF_HOOK+0x328/0x3d4 include/linux/netfilter.h:314 ipv6_rcv+0x9c/0xbc net/ipv6/ip6_input.c:310 __netif_receive_skb_one_core net/core/dev.c:5625 [inline] __netif_receive_skb+0x18c/0x3c8 net/core/dev.c:5739 netif_receive_skb_internal net/core/dev.c:5825 [inline] netif_receive_skb+0x1f0/0x93c net/core/dev.c:5885 tun_rx_batched+0x568/0x6e4 tun_get_user+0x260c/0x3978 drivers/net/tun.c:2002 tun_chr_write_iter+0xfc/0x204 drivers/net/tun.c:2048 new_sync_write fs/read_write.c:497 [inline] vfs_write+0x8f8/0xc38 fs/read_write.c:590 ksys_write+0x15c/0x26c fs/read_write.c:643 __do_sys_write fs/read_write.c:655 [inline] __se_sys_write fs/read_write.c:652 [inline] __arm64_sys_write+0x7c/0x90 fs/read_write.c:652 __invoke_syscall arch/arm64/kernel/syscall.c:34 [inline] invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:48 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:131 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:150 el0_svc+0x54/0x168 arch/arm64/kernel/entry-common.c:712 el0t_64_sync_handler+0x84/0xfc arch/arm64/kernel/entry-common.c:730 el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:598 Code: d2d00015 f2fbfff5 8b080294 d343fe88 (38756908) ---[ end trace 0000000000000000 ]--- ---------------- Code disassembly (best guess): 0: d2d00015 mov x21, #0x800000000000 // #140737488355328 4: f2fbfff5 movk x21, #0xdfff, lsl #48 8: 8b080294 add x20, x20, x8 c: d343fe88 lsr x8, x20, #3 * 10: 38756908 ldrb w8, [x8, x21] <-- trapping instruction Reported-by: syzbot+6acef9e0a4d1f46c83d4@syzkaller.appspotmail.com Fixes: 628bc3e5a1be ("l2tp: Support several sockets with same IP/port quadruple") Signed-off-by: James Chapman --- net/l2tp/l2tp_core.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c index 88a34db265d8..c5a6cfcf1b3f 100644 --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -1523,6 +1523,8 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net, goto err; } + tunnel->l2tp_net = net; + sk = sock->sk; lock_sock(sk); write_lock_bh(&sk->sk_callback_lock); @@ -1551,7 +1553,6 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net, sock_hold(sk); tunnel->sock = sk; - tunnel->l2tp_net = net; spin_lock_bh(&pn->l2tp_tunnel_idr_lock); idr_replace(&pn->l2tp_tunnel_idr, tunnel, tunnel->tunnel_id); -- 2.34.1