[PATCH 5.10 076/111] tcp: defer shutdown(SEND_SHUTDOWN) for TCP_SYN_RECV sockets

Greg Kroah-Hartman
2024-05-14T11:49:40Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 94062790aedb505bdda209b10bea47b294d6394f ]

TCP_SYN_RECV state is really special, it is only used by
cross-syn connections, mostly used by fuzzers.

In the following crash [1], syzbot managed to trigger a divide
by zero in tcp_rcv_space_adjust()

A socket makes the following state transitions,
without ever calling tcp_init_transfer(),
meaning tcp_init_buffer_space() is also not called.

TCP_CLOSE
connect()
TCP_SYN_SENT
TCP_SYN_RECV
shutdown() -> tcp_shutdown(sk, SEND_SHUTDOWN)
TCP_FIN_WAIT1

To fix this issue, change tcp_shutdown() to not
perform a TCP_SYN_RECV -> TCP_FIN_WAIT1 transition,
which makes no sense anyway.

When tcp_rcv_state_process() later changes socket state
from TCP_SYN_RECV to TCP_ESTABLISH, then look at
sk->sk_shutdown to finally enter TCP_FIN_WAIT1 state,
and send a FIN packet from a sane socket state.

This means tcp_send_fin() can now be called from BH
context, and must use GFP_ATOMIC allocations.

[1]
divide error: 0000 [#1] PREEMPT SMP KASAN NOPTI
CPU: 1 PID: 5084 Comm: syz-executor358 Not tainted 6.9.0-rc6-syzkaller-00022-g98369dccd2f8 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
RIP: 0010:tcp_rcv_space_adjust+0x2df/0x890 net/ipv4/tcp_input.c:767
Code: e3 04 4c 01 eb 48 8b 44 24 38 0f b6 04 10 84 c0 49 89 d5 0f 85 a5 03 00 00 41 8b 8e c8 09 00 00 89 e8 29 c8 48 0f af c3 31 d2 <48> f7 f1 48 8d 1c 43 49 8d 96 76 08 00 00 48 89 d0 48 c1 e8 03 48
RSP: 0018:ffffc900031ef3f0 EFLAGS: 00010246
RAX: 0c677a10441f8f42 RBX: 000000004fb95e7e RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000027d4b11f R08: ffffffff89e535a4 R09: 1ffffffff25e6ab7
R10: dffffc0000000000 R11: ffffffff8135e920 R12: ffff88802a9f8d30
R13: dffffc0000000000 R14: ffff88802a9f8d00 R15: 1ffff1100553f2da
FS: 00005555775c0380(0000) GS:ffff8880b9500000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f1155bf2304 CR3: 000000002b9f2000 CR4: 0000000000350ef0
Call Trace:
<TASK>
tcp_recvmsg_locked+0x106d/0x25a0 net/ipv4/tcp.c:2513
tcp_recvmsg+0x25d/0x920 net/ipv4/tcp.c:2578
inet6_recvmsg+0x16a/0x730 net/ipv6/af_inet6.c:680
sock_recvmsg_nosec net/socket.c:1046 [inline]
sock_recvmsg+0x109/0x280 net/socket.c:1068
____sys_recvmsg+0x1db/0x470 net/socket.c:2803
___sys_recvmsg net/socket.c:2845 [inline]
do_recvmmsg+0x474/0xae0 net/socket.c:2939
__sys_recvmmsg net/socket.c:3018 [inline]
__do_sys_recvmmsg net/socket.c:3041 [inline]
__se_sys_recvmmsg net/socket.c:3034 [inline]
__x64_sys_recvmmsg+0x199/0x250 net/socket.c:3034
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7faeb6363db9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 c1 17 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffcc1997168 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007faeb6363db9
RDX: 0000000000000001 RSI: 0000000020000bc0 RDI: 0000000000000005
RBP: 0000000000000000 R08: 0000000000000000 R09: 000000000000001c
R10: 0000000000000122 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000001

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Link: https://lore.kernel.org/r/20240501125448.896529-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/ipv4/tcp.c | 4 ++--
net/ipv4/tcp_input.c | 2 ++
net/ipv4/tcp_output.c | 4 +++-
3 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index ac6cb2dc60380..4ed0d303791a1 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2493,7 +2493,7 @@ void tcp_shutdown(struct sock *sk, int how)
/* If we've already sent a FIN, or it's a closed state, skip this. */
if ((1 << sk->sk_state) &
(TCPF_ESTABLISHED | TCPF_SYN_SENT |
- TCPF_SYN_RECV | TCPF_CLOSE_WAIT)) {
+ TCPF_CLOSE_WAIT)) {
/* Clear out any half completed packets. FIN if needed. */
if (tcp_close_state(sk))
tcp_send_fin(sk);
@@ -2604,7 +2604,7 @@ void __tcp_close(struct sock *sk, long timeout)
* machine. State transitions:
*
* TCP_ESTABLISHED -> TCP_FIN_WAIT1
- * TCP_SYN_RECV -> TCP_FIN_WAIT1 (forget it, it's impossible)
+ * TCP_SYN_RECV -> TCP_FIN_WAIT1 (it is difficult)
* TCP_CLOSE_WAIT -> TCP_LAST_ACK
*
* are legal only when FIN has been sent (i.e. in window),
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 0f9fe5edad142..512f8dc051c61 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6516,6 +6516,8 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)

tcp_initialize_rcv_mss(sk);
tcp_fast_path_on(tp);
+ if (sk->sk_shutdown & SEND_SHUTDOWN)
+ tcp_shutdown(sk, SEND_SHUTDOWN);
break;

case TCP_FIN_WAIT1: {
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index f0df14782ee01..68f1633c477ae 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3440,7 +3440,9 @@ void tcp_send_fin(struct sock *sk)
return;
}
} else {
- skb = alloc_skb_fclone(MAX_TCP_HEADER, sk->sk_allocation);
+ skb = alloc_skb_fclone(MAX_TCP_HEADER,
+ sk_gfp_mask(sk, GFP_ATOMIC |
+ __GFP_NOWARN));
if (unlikely(!skb))
return;

--
2.43.0