Date: Thu, 14 Mar 2024 15:09:05 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: syzbot <syzbot+c669c1136495a2e7c31f@...kaller.appspotmail.com>
Cc: davem@...emloft.net, kuba@...nel.org, linux-kernel@...r.kernel.org, 
	netdev@...r.kernel.org, pabeni@...hat.com, syzkaller-bugs@...glegroups.com, 
	willemdebruijn.kernel@...il.com
Subject: Re: [syzbot] [net?] KCSAN: data-race in dev_queue_xmit_nit / packet_setsockopt

On Thu, Mar 14, 2024 at 3:06 PM syzbot
<syzbot+c669c1136495a2e7c31f@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    480e035fc4c7 Merge tag 'drm-next-2024-03-13' of https://gi..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=11e6a901180000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=943916f31352dd09
> dashboard link: https://syzkaller.appspot.com/bug?extid=c669c1136495a2e7c31f
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/6e7a2dd336dc/disk-480e035f.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/8cb00a02987d/vmlinux-480e035f.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/f325a1992de8/bzImage-480e035f.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+c669c1136495a2e7c31f@...kaller.appspotmail.com
>
> ==================================================================
> BUG: KCSAN: data-race in dev_queue_xmit_nit / packet_setsockopt
>
> write to 0xffff888107804542 of 1 bytes by task 22618 on cpu 0:
>  packet_setsockopt+0xd83/0xfd0 net/packet/af_packet.c:4003
>  do_sock_setsockopt net/socket.c:2311 [inline]
>  __sys_setsockopt+0x1d8/0x250 net/socket.c:2334
>  __do_sys_setsockopt net/socket.c:2343 [inline]
>  __se_sys_setsockopt net/socket.c:2340 [inline]
>  __x64_sys_setsockopt+0x66/0x80 net/socket.c:2340
>  do_syscall_64+0xd3/0x1d0
>  entry_SYSCALL_64_after_hwframe+0x6d/0x75
>
> read to 0xffff888107804542 of 1 bytes by task 27 on cpu 1:
>  dev_queue_xmit_nit+0x82/0x620 net/core/dev.c:2248
>  xmit_one net/core/dev.c:3527 [inline]
>  dev_hard_start_xmit+0xcc/0x3f0 net/core/dev.c:3547
>  __dev_queue_xmit+0xf24/0x1dd0 net/core/dev.c:4335
>  dev_queue_xmit include/linux/netdevice.h:3091 [inline]
>  batadv_send_skb_packet+0x264/0x300 net/batman-adv/send.c:108
>  batadv_send_broadcast_skb+0x24/0x30 net/batman-adv/send.c:127
>  batadv_iv_ogm_send_to_if net/batman-adv/bat_iv_ogm.c:392 [inline]
>  batadv_iv_ogm_emit net/batman-adv/bat_iv_ogm.c:420 [inline]
>  batadv_iv_send_outstanding_bat_ogm_packet+0x3f0/0x4b0 net/batman-adv/bat_iv_ogm.c:1700
>  process_one_work kernel/workqueue.c:3254 [inline]
>  process_scheduled_works+0x465/0x990 kernel/workqueue.c:3335
>  worker_thread+0x526/0x730 kernel/workqueue.c:3416
>  kthread+0x1d1/0x210 kernel/kthread.c:388
>  ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243
>
> value changed: 0x00 -> 0x01
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 1 PID: 27 Comm: kworker/u8:1 Tainted: G        W          6.8.0-syzkaller-08073-g480e035fc4c7 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/29/2024
> Workqueue: bat_events batadv_iv_send_outstanding_bat_ogm_packet
> ==================================================================
>
>
> ---
> 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@...glegroups.com.
>
> syzbot will keep track of this issue. See:
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>
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
>
> If you want to overwrite report's subsystems, reply with:
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>
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
>
> If you want to undo deduplication, reply with:
> #syz undup

I will submit this fix soon:

diff --git a/net/core/dev.c b/net/core/dev.c
index 0766a245816bdf70f6609dc7b6d694ae81e7a9e5..722787c3275527f1652ec98623f61500ee753b45
100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2245,7 +2245,7 @@ void dev_queue_xmit_nit(struct sk_buff *skb,
struct net_device *dev)
        rcu_read_lock();
 again:
        list_for_each_entry_rcu(ptype, ptype_list, list) {
-               if (ptype->ignore_outgoing)
+               if (READ_ONCE(ptype->ignore_outgoing))
                        continue;

                /* Never send packets back to the socket
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 61270826b9ac73e66f9011c3230d4668f0bf7c77..7cfc7d301508fcead214fbdb4e962b0553a17916
100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -4000,7 +4000,7 @@ packet_setsockopt(struct socket *sock, int
level, int optname, sockptr_t optval,
                if (val < 0 || val > 1)
                        return -EINVAL;

-               po->prot_hook.ignore_outgoing = !!val;
+               WRITE_ONCE(po->prot_hook.ignore_outgoing, !!val);
                return 0;
        }
        case PACKET_TX_HAS_OFF:
@@ -4134,7 +4134,7 @@ static int packet_getsockopt(struct socket
*sock, int level, int optname,
                       0);
                break;
        case PACKET_IGNORE_OUTGOING:
-               val = po->prot_hook.ignore_outgoing;
+               val = READ_ONCE(po->prot_hook.ignore_outgoing);
                break;
        case PACKET_ROLLOVER_STATS:
                if (!po->rollover)

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