Re: [syzbot] WARNING: suspicious RCU usage in bpf_sk_reuseport_detach

[Daniel Borkmann]

[ +Hawkins ]

On 8/15/22 12:59 PM, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    94ce3b64c62d net/tls: Use RCU API to access tls_ctx->netdev
> git tree:       net
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=14641e15080000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=53da55f2bdeb0d4c
> dashboard link: https://syzkaller.appspot.com/bug?extid=24bcff6e82ce253f23ec
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=106c89fd080000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17ead885080000
>
> The issue was bisected to:
>
> commit f72c38fad234759fe943cb2e40bf3d0f7de1d4d9
> Author: Edward Cree <ecree.xilinx@xxxxxxxxx>
> Date:   Wed Jul 20 18:33:48 2022 +0000
>
>      sfc: hook up ef100 representor TX

Looks rather related to:

commit 2a0133723f9ebeb751cfce19f74ec07e108bef1f
Author: Hawkins Jiawei <yin31149@xxxxxxxxx>
Date:   Fri Aug 5 15:48:34 2022 +0800

    net: fix refcount bug in sk_psock_get (2)

> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=125bf9fd080000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=115bf9fd080000
> console output: https://syzkaller.appspot.com/x/log.txt?x=165bf9fd080000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+24bcff6e82ce253f23ec@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: f72c38fad234 ("sfc: hook up ef100 representor TX")
>
> =============================
> WARNING: suspicious RCU usage
> 5.19.0-syzkaller-05408-g94ce3b64c62d #0 Not tainted
> -----------------------------
> include/net/sock.h:592 suspicious rcu_dereference_check() usage!
>
> other info that might help us debug this:
>
>
> rcu_scheduler_active = 2, debug_locks = 1
> 4 locks held by syz-executor334/3611:
>   #0: ffff888073b7be10 (&sb->s_type->i_mutex_key#10){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:760 [inline]
>   #0: ffff888073b7be10 (&sb->s_type->i_mutex_key#10){+.+.}-{3:3}, at: __sock_release+0x86/0x280 net/socket.c:649
>   #1: ffffc900014e5c28 (&table->hash[i].lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:354 [inline]
>   #1: ffffc900014e5c28 (&table->hash[i].lock){+...}-{2:2}, at: udp_lib_unhash net/ipv4/udp.c:2014 [inline]
>   #1: ffffc900014e5c28 (&table->hash[i].lock){+...}-{2:2}, at: udp_lib_unhash+0x1d5/0x730 net/ipv4/udp.c:2004
>   #2: ffffffff8d7a9a78 (reuseport_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:354 [inline]
>   #2: ffffffff8d7a9a78 (reuseport_lock){+...}-{2:2}, at: reuseport_detach_sock+0x22/0x4a0 net/core/sock_reuseport.c:346
>   #3: ffff888145f9a0b8 (clock-AF_INET){++..}-{2:2}, at: bpf_sk_reuseport_detach+0x26/0x190 kernel/bpf/reuseport_array.c:26
>
> stack backtrace:
> CPU: 1 PID: 3611 Comm: syz-executor334 Not tainted 5.19.0-syzkaller-05408-g94ce3b64c62d #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022
> Call Trace:
>   <TASK>
>   __dump_stack lib/dump_stack.c:88 [inline]
>   dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
>   __rcu_dereference_sk_user_data_with_flags include/net/sock.h:592 [inline]
>   bpf_sk_reuseport_detach+0x156/0x190 kernel/bpf/reuseport_array.c:27
>   reuseport_detach_sock+0x8c/0x4a0 net/core/sock_reuseport.c:362
>   udp_lib_unhash net/ipv4/udp.c:2016 [inline]
>   udp_lib_unhash+0x210/0x730 net/ipv4/udp.c:2004
>   sk_common_release+0xba/0x390 net/core/sock.c:3600
>   inet_release+0x12e/0x280 net/ipv4/af_inet.c:428
>   __sock_release+0xcd/0x280 net/socket.c:650
>   sock_close+0x18/0x20 net/socket.c:1365
>   __fput+0x277/0x9d0 fs/file_table.c:320
>   task_work_run+0xdd/0x1a0 kernel/task_work.c:177
>   exit_task_work include/linux/task_work.h:38 [inline]
>   do_exit+0xade/0x29d0 kernel/exit.c:795
>   do_group_exit+0xd2/0x2f0 kernel/exit.c:925
>   __do_sys_exit_group kernel/exit.c:936 [inline]
>   __se_sys_exit_group kernel/exit.c:934 [inline]
>   __x64_sys_exit_group+0x3a/0x50 kernel/exit.c:934
>   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>   do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>   entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7fe407d09699
> Code: Unable to access opcode bytes at RIP 0x7fe407d0966f.
> RSP: 002b:00007ffc0ff152a8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
>
>
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx.
>
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> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this issue, for details see:
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