netdev - Re: [PATCH net] tcp: deny tcp_disconnect() when threads are waiting

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Date: Mon, 29 May 2023 11:55:55 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Eric Dumazet <edumazet@...gle.com>, "David S . Miller"
 <davem@...emloft.net>,  Jakub Kicinski <kuba@...nel.org>
Cc: netdev@...r.kernel.org, eric.dumazet@...il.com, syzbot
	 <syzkaller@...glegroups.com>
Subject: Re: [PATCH net] tcp: deny tcp_disconnect() when threads are waiting

On Fri, 2023-05-26 at 16:34 +0000, Eric Dumazet wrote:
> Historically connect(AF_UNSPEC) has been abused by syzkaller
> and other fuzzers to trigger various bugs.
> 
> A recent one triggers a divide-by-zero [1], and Paolo Abeni
> was able to diagnose the issue.
> 
> tcp_recvmsg_locked() has tests about sk_state being not TCP_LISTEN
> and TCP REPAIR mode being not used.
> 
> Then later if socket lock is released in sk_wait_data(),
> another thread can call connect(AF_UNSPEC), then make this
> socket a TCP listener.
> 
> When recvmsg() is resumed, it can eventually call tcp_cleanup_rbuf()
> and attempt a divide by 0 in tcp_rcv_space_adjust() [1]
> 
> This patch adds a new socket field, counting number of threads
> blocked in sk_wait_event() and inet_wait_for_connect().
> 
> If this counter is not zero, tcp_disconnect() returns an error.
> 
> This patch adds code in blocking socket system calls, thus should
> not hurt performance of non blocking ones.
> 
> Note that we probably could revert commit 499350a5a6e7 ("tcp:
> initialize rcv_mss to TCP_MIN_MSS instead of 0") to restore
> original tcpi_rcv_mss meaning (was 0 if no payload was ever
> received on a socket)
> 
> [1]
> divide error: 0000 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 13832 Comm: syz-executor.5 Not tainted 6.3.0-rc4-syzkaller-00224-g00c7b5f4ddc5 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
> RIP: 0010:tcp_rcv_space_adjust+0x36e/0x9d0 net/ipv4/tcp_input.c:740
> Code: 00 00 00 00 fc ff df 4c 89 64 24 48 8b 44 24 04 44 89 f9 41 81 c7 80 03 00 00 c1 e1 04 44 29 f0 48 63 c9 48 01 e9 48 0f af c1 <49> f7 f6 48 8d 04 41 48 89 44 24 40 48 8b 44 24 30 48 c1 e8 03 48
> RSP: 0018:ffffc900033af660 EFLAGS: 00010206
> RAX: 4a66b76cbade2c48 RBX: ffff888076640cc0 RCX: 00000000c334e4ac
> RDX: 0000000000000000 RSI: dffffc0000000000 RDI: 0000000000000001
> RBP: 00000000c324e86c R08: 0000000000000001 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: ffff8880766417f8
> R13: ffff888028fbb980 R14: 0000000000000000 R15: 0000000000010344
> FS: 00007f5bffbfe700(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000001b32f25000 CR3: 000000007ced0000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> <TASK>
> tcp_recvmsg_locked+0x100e/0x22e0 net/ipv4/tcp.c:2616
> tcp_recvmsg+0x117/0x620 net/ipv4/tcp.c:2681
> inet6_recvmsg+0x114/0x640 net/ipv6/af_inet6.c:670
> sock_recvmsg_nosec net/socket.c:1017 [inline]
> sock_recvmsg+0xe2/0x160 net/socket.c:1038
> ____sys_recvmsg+0x210/0x5a0 net/socket.c:2720
> ___sys_recvmsg+0xf2/0x180 net/socket.c:2762
> do_recvmmsg+0x25e/0x6e0 net/socket.c:2856
> __sys_recvmmsg net/socket.c:2935 [inline]
> __do_sys_recvmmsg net/socket.c:2958 [inline]
> __se_sys_recvmmsg net/socket.c:2951 [inline]
> __x64_sys_recvmmsg+0x20f/0x260 net/socket.c:2951
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7f5c0108c0f9
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 f1 19 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:00007f5bffbfe168 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
> RAX: ffffffffffffffda RBX: 00007f5c011ac050 RCX: 00007f5c0108c0f9
> RDX: 0000000000000001 RSI: 0000000020000bc0 RDI: 0000000000000003
> RBP: 00007f5c010e7b39 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000122 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f5c012cfb1f R14: 00007f5bffbfe300 R15: 0000000000022000
> </TASK>
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Reported-by: syzbot <syzkaller@...glegroups.com>
> Reported-by: Paolo Abeni <pabeni@...hat.com>
> Diagnosed-by: Paolo Abeni <pabeni@...hat.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Thanks Eric!

FWIW I gave this a spin in my testbed and solves the issue for me.

Tested-by: Paolo Abeni <pabeni@...hat.com>