On 02.04.2018 12:20, syzbot wrote:
> Hello,
>
> syzbot hit the following crash on net-next commit
> 06b19fe9a6df7aaa423cd8404ebe5ac9ec4b2960 (Sun Apr 1 03:37:33 2018 +0000)
> Merge branch 'chelsio-inline-tls'
> syzbot dashboard link:
> https://syzkaller.appspot.com/bug?extid=6b495100f17ca8554ab9
>
> Unfortunately, I don't have any reproducer for this crash yet.
> Raw console output:
> https://syzkaller.appspot.com/x/log.txt?id=6218830443446272
> Kernel config: https://syzkaller.appspot.com/x/.config?id=3327544840960562528
> compiler: gcc (GCC) 7.1.1 20170620
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+6b495100f17ca8554...@syzkaller.appspotmail.com
> It will help syzbot understand when the bug is fixed. See footer for details.
> If you forward the report, please keep this part and the footer.
>
>
> ======================================================
> WARNING: possible circular locking dependency detected
> 4.16.0-rc6+ #290 Not tainted
> ------------------------------------------------------
> syz-executor7/20971 is trying to acquire lock:
> (&af_unix_sk_receive_queue_lock_key){+.+.}, at: [<00000000271ef0d8>]
> skb_queue_tail+0x26/0x150 net/core/skbuff.c:2899
>
> but task is already holding lock:
> (&(&u->lock)->rlock/1){+.+.}, at: [<000000004e725e14>]
> unix_state_double_lock+0x7b/0xb0 net/unix/af_unix.c:1088
>
> which lock already depends on the new lock.
>
>
> the existing dependency chain (in reverse order) is:
>
> -> #1 (&(&u->lock)->rlock/1){+.+.}:
> _raw_spin_lock_nested+0x28/0x40 kernel/locking/spinlock.c:354
> sk_diag_dump_icons net/unix/diag.c:82 [inline]
> sk_diag_fill.isra.4+0xa52/0xfe0 net/unix/diag.c:144
> sk_diag_dump net/unix/diag.c:178 [inline]
> unix_diag_dump+0x400/0x4f0 net/unix/diag.c:206
> netlink_dump+0x492/0xcf0 net/netlink/af_netlink.c:2221
> __netlink_dump_start+0x4ec/0x710 net/netlink/af_netlink.c:2318
> netlink_dump_start include/linux/netlink.h:214 [inline]
> unix_diag_handler_dump+0x3e7/0x750 net/unix/diag.c:307
> __sock_diag_cmd net/core/sock_diag.c:230 [inline]
> sock_diag_rcv_msg+0x204/0x360 net/core/sock_diag.c:261
> netlink_rcv_skb+0x14b/0x380 net/netlink/af_netlink.c:2443
> sock_diag_rcv+0x2a/0x40 net/core/sock_diag.c:272
> netlink_unicast_kernel net/netlink/af_netlink.c:1307 [inline]
> netlink_unicast+0x4c4/0x6b0 net/netlink/af_netlink.c:1333
> netlink_sendmsg+0xa4a/0xe80 net/netlink/af_netlink.c:1896
> sock_sendmsg_nosec net/socket.c:629 [inline]
> sock_sendmsg+0xca/0x110 net/socket.c:639
> sock_write_iter+0x31a/0x5d0 net/socket.c:908
> call_write_iter include/linux/fs.h:1782 [inline]
> new_sync_write fs/read_write.c:469 [inline]
> __vfs_write+0x684/0x970 fs/read_write.c:482
> vfs_write+0x189/0x510 fs/read_write.c:544
> SYSC_write fs/read_write.c:589 [inline]
> SyS_write+0xef/0x220 fs/read_write.c:581
> do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
> entry_SYSCALL_64_after_hwframe+0x42/0xb7
>
> -> #0 (&af_unix_sk_receive_queue_lock_key){+.+.}:
> lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3920
> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> _raw_spin_lock_irqsave+0x96/0xc0 kernel/locking/spinlock.c:152
> skb_queue_tail+0x26/0x150 net/core/skbuff.c:2899
> unix_dgram_sendmsg+0xa30/0x1610 net/unix/af_unix.c:1807
> sock_sendmsg_nosec net/socket.c:629 [inline]
> sock_sendmsg+0xca/0x110 net/socket.c:639
> ___sys_sendmsg+0x320/0x8b0 net/socket.c:2047
> __sys_sendmmsg+0x1ee/0x620 net/socket.c:2137
> SYSC_sendmmsg net/socket.c:2168 [inline]
> SyS_sendmmsg+0x35/0x60 net/socket.c:2163
> do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
> entry_SYSCALL_64_after_hwframe+0x42/0xb7
sk_diag_dump_icons() dumps only sockets in TCP_LISTEN state.
TCP_LISTEN state may be assigned in only place in net/unix/af_unix.c:
it's unix_listen(). The function is applied to stream and seqpacket
socket types.
It can't be stream because of the second stack, and seqpacket also can't,
as I don't think it's possible for gcc to inline unix_seqpacket_sendmsg()
in the way, we don't see it in the stack.
So, this is looks like false positive result for me.
Kirill
>
> other info that might help us debug this:
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(&(&u->lock)->rlock/1);
> lock(&af_unix_sk_receive_queue_lock_key);
> lock(&(&u->lock)->rlock/1);
> lock(&af_unix_sk_receive_queue_lock_key);
>
> *** DEADLOCK ***
>
> 1 lock held by syz-executor7/20971:
> #0: (&(&u->lock)->rlock/1){+.+.}, at: [<000000004e725e14>]
> unix_state_double_lock+0x7b/0xb0 net/unix/af_unix.c:1088
>
> stack backtrace:
> CPU: 0 PID: 20971 Comm: syz-executor7 Not tainted 4.16.0-rc6+ #290
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
> __dump_stack lib/dump_stack.c:17 [inline]
> dump_stack+0x194/0x24d lib/dump_stack.c:53
> print_circular_bug.isra.38+0x2cd/0x2dc kernel/locking/lockdep.c:1223
> check_prev_add kernel/locking/lockdep.c:1863 [inline]
> check_prevs_add kernel/locking/lockdep.c:1976 [inline]
> validate_chain kernel/locking/lockdep.c:2417 [inline]
> __lock_acquire+0x30a8/0x3e00 kernel/locking/lockdep.c:3431
> lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3920
> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> _raw_spin_lock_irqsave+0x96/0xc0 kernel/locking/spinlock.c:152
> skb_queue_tail+0x26/0x150 net/core/skbuff.c:2899
> unix_dgram_sendmsg+0xa30/0x1610 net/unix/af_unix.c:1807
> sock_sendmsg_nosec net/socket.c:629 [inline]
> sock_sendmsg+0xca/0x110 net/socket.c:639
> ___sys_sendmsg+0x320/0x8b0 net/socket.c:2047
> __sys_sendmmsg+0x1ee/0x620 net/socket.c:2137
> SYSC_sendmmsg net/socket.c:2168 [inline]
> SyS_sendmmsg+0x35/0x60 net/socket.c:2163
> do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
> entry_SYSCALL_64_after_hwframe+0x42/0xb7
> RIP: 0033:0x455269
> RSP: 002b:00007f71ffad6c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
> RAX: ffffffffffffffda RBX: 00007f71ffad76d4 RCX: 0000000000455269
> RDX: 04924924924924f4 RSI: 0000000020000200 RDI: 0000000000000016
> RBP: 000000000072bf58 R08: 0000000000000000 R09: 0000000000000000
> R10: 00000000200000d4 R11: 0000000000000246 R12: 00000000ffffffff
> R13: 00000000000004ca R14: 00000000006f9390 R15: 0000000000000001
> IPVS: Unknown mcast interface: bcsh0
> IPVS: Unknown mcast interface: bcsh0
> IPVS: Unknown mcast interface: bcsh0
> IPVS: Unknown mcast interface: bcsh0
> IPVS: Unknown mcast interface: bcsh0
> IPVS: Unknown mcast interface: bcsh0
> IPVS: Unknown mcast interface: bcsh0
> IPVS: Unknown mcast interface: bcsh0
> IPVS: Unknown mcast interface: bcsh0
> IPVS: sync thread started: state = BACKUP, mcast_ifn = bcsh0, syncid = 0, id
> = 0
> IPVS: Unknown mcast interface: bcsh0
> IPVS: Unknown mcast interface: bcsh0
> IPVS: Unknown mcast interface: bcsh0
> IPVS: Unknown mcast interface: bcsh0
> IPVS: Unknown mcast interface: bcsh0
> IPVS: Unknown mcast interface: bcsh0
> IPVS: Unknown mcast interface: bcsh0
> IPVS: Unknown mcast interface: bcsh0
>
>
> ---
> This bug is generated by a dumb bot. It may contain errors.
> See https://goo.gl/tpsmEJ for details.
> Direct all questions to syzkal...@googlegroups.com.
>
> syzbot will keep track of this bug report.
> If you forgot to add the Reported-by tag, once the fix for this bug is merged
> into any tree, please reply to this email with:
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