netdev - Re: [PATCH v2 net] sctp: Fix null-ptr-deref in reuseport_add

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Message-ID: <CADvbK_eRc7pgp_E95hjWK4wBSnY7RAtmqi3wPk+0+7f1O06p5w@mail.gmail.com>
Date: Fri, 2 Aug 2024 11:25:05 -0400
From: Xin Long <lucien.xin@...il.com>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org, linux-sctp@...r.kernel.org, 
	syzbot+e6979a5d2f10ecb700e4@...kaller.appspotmail.com
Subject: Re: [PATCH v2 net] sctp: Fix null-ptr-deref in reuseport_add_sock().

On Wed, Jul 31, 2024 at 7:46 PM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
>
> syzbot reported a null-ptr-deref while accessing sk2->sk_reuseport_cb in
> reuseport_add_sock(). [0]
>
> The repro first creates a listener with SO_REUSEPORT.  Then, it creates
> another listener on the same port and concurrently closes the first
> listener.
>
> The second listen() calls reuseport_add_sock() with the first listener as
> sk2, where sk2->sk_reuseport_cb is not expected to be cleared concurrently,
> but the close() does clear it by reuseport_detach_sock().
>
> The problem is SCTP does not properly synchronise reuseport_alloc(),
> reuseport_add_sock(), and reuseport_detach_sock().
>
> The caller of reuseport_alloc() and reuseport_{add,detach}_sock() must
> provide synchronisation for sockets that are classified into the same
> reuseport group.
>
> Otherwise, such sockets form multiple identical reuseport groups, and
> all groups except one would be silently dead.
>
>   1. Two sockets call listen() concurrently
>   2. No socket in the same group found in sctp_ep_hashtable[]
>   3. Two sockets call reuseport_alloc() and form two reuseport groups
>   4. Only one group hit first in __sctp_rcv_lookup_endpoint() receives
>       incoming packets
>
> Also, the reported null-ptr-deref could occur.
>
> TCP/UDP guarantees that would not happen by holding the hash bucket lock.
>
> Let's apply the locking strategy to __sctp_hash_endpoint() and
> __sctp_unhash_endpoint().
>
> [0]:
> Oops: general protection fault, probably for non-canonical address 0xdffffc0000000002: 0000 [#1] PREEMPT SMP KASAN PTI
> KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
> CPU: 1 UID: 0 PID: 10230 Comm: syz-executor119 Not tainted 6.10.0-syzkaller-12585-g301927d2d2eb #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/27/2024
> RIP: 0010:reuseport_add_sock+0x27e/0x5e0 net/core/sock_reuseport.c:350
> Code: 00 0f b7 5d 00 bf 01 00 00 00 89 de e8 1b a4 ff f7 83 fb 01 0f 85 a3 01 00 00 e8 6d a0 ff f7 49 8d 7e 12 48 89 f8 48 c1 e8 03 <42> 0f b6 04 28 84 c0 0f 85 4b 02 00 00 41 0f b7 5e 12 49 8d 7e 14
> RSP: 0018:ffffc9000b947c98 EFLAGS: 00010202
> RAX: 0000000000000002 RBX: ffff8880252ddf98 RCX: ffff888079478000
> RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000012
> RBP: 0000000000000001 R08: ffffffff8993e18d R09: 1ffffffff1fef385
> R10: dffffc0000000000 R11: fffffbfff1fef386 R12: ffff8880252ddac0
> R13: dffffc0000000000 R14: 0000000000000000 R15: 0000000000000000
> FS:  00007f24e45b96c0(0000) GS:ffff8880b9300000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007ffcced5f7b8 CR3: 00000000241be000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  __sctp_hash_endpoint net/sctp/input.c:762 [inline]
>  sctp_hash_endpoint+0x52a/0x600 net/sctp/input.c:790
>  sctp_listen_start net/sctp/socket.c:8570 [inline]
>  sctp_inet_listen+0x767/0xa20 net/sctp/socket.c:8625
>  __sys_listen_socket net/socket.c:1883 [inline]
>  __sys_listen+0x1b7/0x230 net/socket.c:1894
>  __do_sys_listen net/socket.c:1902 [inline]
>  __se_sys_listen net/socket.c:1900 [inline]
>  __x64_sys_listen+0x5a/0x70 net/socket.c:1900
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f24e46039b9
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 91 1a 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 b0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f24e45b9228 EFLAGS: 00000246 ORIG_RAX: 0000000000000032
> RAX: ffffffffffffffda RBX: 00007f24e468e428 RCX: 00007f24e46039b9
> RDX: 00007f24e46039b9 RSI: 0000000000000003 RDI: 0000000000000004
> RBP: 00007f24e468e420 R08: 00007f24e45b96c0 R09: 00007f24e45b96c0
> R10: 00007f24e45b96c0 R11: 0000000000000246 R12: 00007f24e468e42c
> R13: 00007f24e465a5dc R14: 0020000000000001 R15: 00007ffcced5f7d8
>  </TASK>
> Modules linked in:
>
> Fixes: 6ba845740267 ("sctp: process sk_reuseport in sctp_get_port_local")
> Reported-by: syzbot+e6979a5d2f10ecb700e4@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=e6979a5d2f10ecb700e4
> Tested-by: syzbot+e6979a5d2f10ecb700e4@...kaller.appspotmail.com
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>

Acked-by: Xin Long <lucien.xin@...il.com>

Thanks.