Re: [syzbot] possible deadlock in sctp_addr_wq_timeout_handler

From: Xin Long
Date: Sat May 01 2021 - 17:27:20 EST

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On Fri, Apr 30, 2021 at 3:19 PM syzbot
<syzbot+959223586843e69a2674@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 2a1d7946 Merge tag 'for-linus' of git://git.kernel.org/pub..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=159af1c1d00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=9404cfa686df2c05
> dashboard link: https://syzkaller.appspot.com/bug?extid=959223586843e69a2674
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11613d71d00000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12be674dd00000
>
> The issue was bisected to:
>
> commit 997acaf6b4b59c6a9c259740312a69ea549cc684
> Author: Mark Rutland <mark.rutland@xxxxxxx>
> Date: Mon Jan 11 15:37:07 2021 +0000
>
> lockdep: report broken irq restoration
>
> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=17c36a5dd00000
> final oops: https://syzkaller.appspot.com/x/report.txt?x=14236a5dd00000
> console output: https://syzkaller.appspot.com/x/log.txt?x=10236a5dd00000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+959223586843e69a2674@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 997acaf6b4b5 ("lockdep: report broken irq restoration")
>
> ======================================================
> WARNING: possible circular locking dependency detected
> 5.12.0-rc8-syzkaller #0 Not tainted
> ------------------------------------------------------
> syz-executor044/8536 is trying to acquire lock:
> ffff8880183933a0 (slock-AF_INET6){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:354 [inline]
> ffff8880183933a0 (slock-AF_INET6){+.-.}-{2:2}, at: sctp_addr_wq_timeout_handler+0x1a1/0x550 net/sctp/protocol.c:666
>
> but task is already holding lock:
> ffffffff8d659620 (&net->sctp.addr_wq_lock){+.-.}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:359 [inline]
> ffffffff8d659620 (&net->sctp.addr_wq_lock){+.-.}-{2:2}, at: sctp_addr_wq_timeout_handler+0x38/0x550 net/sctp/protocol.c:626
>
> which lock already depends on the new lock.
>
>
> the existing dependency chain (in reverse order) is:
>
> -> #1 (&net->sctp.addr_wq_lock){+.-.}-{2:2}:
> __raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]
> _raw_spin_lock_bh+0x2f/0x40 kernel/locking/spinlock.c:175
> spin_lock_bh include/linux/spinlock.h:359 [inline]
> sctp_destroy_sock+0x204/0x440 net/sctp/socket.c:5028
> sctp_v6_destroy_sock+0x11/0x20 net/sctp/socket.c:9528
> sk_common_release+0x64/0x390 net/core/sock.c:3264
> sctp_close+0x4da/0x940 net/sctp/socket.c:1531
> inet_release+0x12e/0x280 net/ipv4/af_inet.c:431
> inet6_release+0x4c/0x70 net/ipv6/af_inet6.c:478
> __sock_release+0xcd/0x280 net/socket.c:599
> sock_close+0x18/0x20 net/socket.c:1258
> __fput+0x288/0x920 fs/file_table.c:280
> task_work_run+0xdd/0x1a0 kernel/task_work.c:140
> exit_task_work include/linux/task_work.h:30 [inline]
> do_exit+0xbfc/0x2a60 kernel/exit.c:825
> do_group_exit+0x125/0x310 kernel/exit.c:922
> __do_sys_exit_group kernel/exit.c:933 [inline]
> __se_sys_exit_group kernel/exit.c:931 [inline]
> __x64_sys_exit_group+0x3a/0x50 kernel/exit.c:931
> do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
> entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> -> #0 (slock-AF_INET6){+.-.}-{2:2}:
> check_prev_add kernel/locking/lockdep.c:2937 [inline]
> check_prevs_add kernel/locking/lockdep.c:3060 [inline]
> validate_chain kernel/locking/lockdep.c:3675 [inline]
> __lock_acquire+0x2b14/0x54c0 kernel/locking/lockdep.c:4901
> lock_acquire kernel/locking/lockdep.c:5511 [inline]
> lock_acquire+0x1ab/0x740 kernel/locking/lockdep.c:5476
> __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
> _raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:151
> spin_lock include/linux/spinlock.h:354 [inline]
> sctp_addr_wq_timeout_handler+0x1a1/0x550 net/sctp/protocol.c:666
> call_timer_fn+0x1a5/0x6b0 kernel/time/timer.c:1431
> expire_timers kernel/time/timer.c:1476 [inline]
> __run_timers.part.0+0x67c/0xa50 kernel/time/timer.c:1745
> __run_timers kernel/time/timer.c:1726 [inline]
> run_timer_softirq+0xb3/0x1d0 kernel/time/timer.c:1758
> __do_softirq+0x29b/0x9f6 kernel/softirq.c:345
> invoke_softirq kernel/softirq.c:221 [inline]
> __irq_exit_rcu kernel/softirq.c:422 [inline]
> irq_exit_rcu+0x134/0x200 kernel/softirq.c:434
> sysvec_apic_timer_interrupt+0x93/0xc0 arch/x86/kernel/apic/apic.c:1100
> asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:632
> __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:161 [inline]
> _raw_spin_unlock_irqrestore+0x38/0x70 kernel/locking/spinlock.c:191
> __debug_check_no_obj_freed lib/debugobjects.c:997 [inline]
> debug_check_no_obj_freed+0x20c/0x420 lib/debugobjects.c:1018
> slab_free_hook mm/slub.c:1554 [inline]
> slab_free_freelist_hook+0x147/0x210 mm/slub.c:1600
> slab_free mm/slub.c:3161 [inline]
> kmem_cache_free+0x8a/0x740 mm/slub.c:3177
> free_fs_struct fs/fs_struct.c:92 [inline]
> exit_fs+0x123/0x170 fs/fs_struct.c:108
> do_exit+0xbca/0x2a60 kernel/exit.c:821
> do_group_exit+0x125/0x310 kernel/exit.c:922
> __do_sys_exit_group kernel/exit.c:933 [inline]
> __se_sys_exit_group kernel/exit.c:931 [inline]
> __x64_sys_exit_group+0x3a/0x50 kernel/exit.c:931
> do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
> entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> other info that might help us debug this:
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(&net->sctp.addr_wq_lock);
> lock(slock-AF_INET6);
> lock(&net->sctp.addr_wq_lock);
> lock(slock-AF_INET6);
Unfortunately, Commit b166a20b0738 ("net/sctp: fix race condition in
sctp_destroy_sock")
introduced this, and had to be reverted. I'm thinking to fix it by
delaying the auto_asconf
until doing bind, which makes more sense, as auto_asconf requires an
ANY addr bind:

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index a710917c5ac7..4ae428f2f2c5 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -357,6 +357,18 @@ static struct sctp_af *sctp_sockaddr_af(struct
sctp_sock *opt,
return af;
}

+static void sctp_auto_asconf_init(struct sctp_sock *sp)
+{
+ struct net *net = sock_net(&sp->inet.sk);
+
+ if (net->sctp.default_auto_asconf) {
+ spin_lock(&net->sctp.addr_wq_lock);
+ list_add_tail(&sp->auto_asconf_list, &net->sctp.auto_asconf_splist);
+ spin_unlock(&net->sctp.addr_wq_lock);
+ sp->do_auto_asconf = 1;
+ }
+}
+
/* Bind a local address either to an endpoint or to an association. */
static int sctp_do_bind(struct sock *sk, union sctp_addr *addr, int len)
{
@@ -418,8 +430,10 @@ static int sctp_do_bind(struct sock *sk, union
sctp_addr *addr, int len)
return -EADDRINUSE;

/* Refresh ephemeral port. */
- if (!bp->port)
+ if (!bp->port) {
bp->port = inet_sk(sk)->inet_num;
+ sctp_auto_asconf_init(sp);
+ }

/* Add the address to the bind address list.
* Use GFP_ATOMIC since BHs will be disabled.
@@ -4993,19 +5007,6 @@ static int sctp_init_sock(struct sock *sk)
sk_sockets_allocated_inc(sk);
sock_prot_inuse_add(net, sk->sk_prot, 1);

- /* Nothing can fail after this block, otherwise
- * sctp_destroy_sock() will be called without addr_wq_lock held
- */
- if (net->sctp.default_auto_asconf) {
- spin_lock(&sock_net(sk)->sctp.addr_wq_lock);
- list_add_tail(&sp->auto_asconf_list,
- &net->sctp.auto_asconf_splist);
- sp->do_auto_asconf = 1;
- spin_unlock(&sock_net(sk)->sctp.addr_wq_lock);
- } else {
- sp->do_auto_asconf = 0;
- }
-
local_bh_enable();

return 0;
@@ -9401,6 +9402,8 @@ static int sctp_sock_migrate(struct sock *oldsk,
struct sock *newsk,
return err;
}

+ sctp_auto_asconf_init(newsp);
+
/* Move any messages in the old socket's receive queue that are for the
* peeled off association to the new socket's receive queue.
*/
--
2.18.1

Thanks.
>
> *** DEADLOCK ***
>
> 2 locks held by syz-executor044/8536:
> #0: ffffc90000007d78 ((&net->sctp.addr_wq_timer)){+.-.}-{0:0}, at: lockdep_copy_map include/linux/lockdep.h:35 [inline]
> #0: ffffc90000007d78 ((&net->sctp.addr_wq_timer)){+.-.}-{0:0}, at: call_timer_fn+0xd5/0x6b0 kernel/time/timer.c:1421
> #1: ffffffff8d659620 (&net->sctp.addr_wq_lock){+.-.}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:359 [inline]
> #1: ffffffff8d659620 (&net->sctp.addr_wq_lock){+.-.}-{2:2}, at: sctp_addr_wq_timeout_handler+0x38/0x550 net/sctp/protocol.c:626
>
> stack backtrace:
> CPU: 0 PID: 8536 Comm: syz-executor044 Not tainted 5.12.0-rc8-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
> <IRQ>
> __dump_stack lib/dump_stack.c:79 [inline]
> dump_stack+0x141/0x1d7 lib/dump_stack.c:120
> check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2128
> check_prev_add kernel/locking/lockdep.c:2937 [inline]
> check_prevs_add kernel/locking/lockdep.c:3060 [inline]
> validate_chain kernel/locking/lockdep.c:3675 [inline]
> __lock_acquire+0x2b14/0x54c0 kernel/locking/lockdep.c:4901
> lock_acquire kernel/locking/lockdep.c:5511 [inline]
> lock_acquire+0x1ab/0x740 kernel/locking/lockdep.c:5476
> __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
> _raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:151
> spin_lock include/linux/spinlock.h:354 [inline]
> sctp_addr_wq_timeout_handler+0x1a1/0x550 net/sctp/protocol.c:666
> call_timer_fn+0x1a5/0x6b0 kernel/time/timer.c:1431
> expire_timers kernel/time/timer.c:1476 [inline]
> __run_timers.part.0+0x67c/0xa50 kernel/time/timer.c:1745
> __run_timers kernel/time/timer.c:1726 [inline]
> run_timer_softirq+0xb3/0x1d0 kernel/time/timer.c:1758
> __do_softirq+0x29b/0x9f6 kernel/softirq.c:345
> invoke_softirq kernel/softirq.c:221 [inline]
> __irq_exit_rcu kernel/softirq.c:422 [inline]
> irq_exit_rcu+0x134/0x200 kernel/softirq.c:434
> sysvec_apic_timer_interrupt+0x93/0xc0 arch/x86/kernel/apic/apic.c:1100
> </IRQ>
> asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:632
> RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:161 [inline]
> RIP: 0010:_raw_spin_unlock_irqrestore+0x38/0x70 kernel/locking/spinlock.c:191
> Code: 74 24 10 e8 4a f9 53 f8 48 89 ef e8 82 af 54 f8 81 e3 00 02 00 00 75 25 9c 58 f6 c4 02 75 2d 48 85 db 74 01 fb bf 01 00 00 00 <e8> 63 7d 48 f8 65 8b 05 0c 48 fc 76 85 c0 74 0a 5b 5d c3 e8 d0 3c
> RSP: 0018:ffffc9000173fc50 EFLAGS: 00000206
> RAX: 0000000000000002 RBX: 0000000000000200 RCX: 1ffffffff1b89e11
> RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000001
> RBP: ffffffff9006cf00 R08: 0000000000000001 R09: 0000000000000001
> R10: ffffffff8179e4c8 R11: 000000000000003f R12: 1ffffffff200d9df
> R13: 0000000000000000 R14: dead000000000100 R15: dffffc0000000000
> __debug_check_no_obj_freed lib/debugobjects.c:997 [inline]
> debug_check_no_obj_freed+0x20c/0x420 lib/debugobjects.c:1018
> slab_free_hook mm/slub.c:1554 [inline]
> slab_free_freelist_hook+0x147/0x210 mm/slub.c:1600
> slab_free mm/slub.c:3161 [inline]
> kmem_cache_free+0x8a/0x740 mm/slub.c:3177
> free_fs_struct fs/fs_struct.c:92 [inline]
> exit_fs+0x123/0x170 fs/fs_struct.c:108
> do_exit+0xbca/0x2a60 kernel/exit.c:821
> do_group_exit+0x125/0x310 kernel/exit.c:922
> __do_sys_exit_group kernel/exit.c:933 [inline]
> __se_sys_exit_group kernel/exit.c:931 [inline]
> __x64_sys_exit_group+0x3a/0x50 kernel/exit.c:931
> do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
> entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x43ea79
> Code: Unable to access opcode bytes at RIP 0x43ea4f.
> RSP: 002b:00007ffdbc348058 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
> RAX: ffffffffffffffda RBX: 00000000004b0330 RCX: 000000000043ea79
> RDX: 000000000000003c RSI: 00000000000000e7 RDI: 0000000000000000
> RBP: 0000000000000000 R08: ffffffffffffffc0 R09: 0000000000000001
> R10: 0000000000000001 R11: 0000000000000246 R12: 00000000004b0330
> R13: 0000000000000001 R14: 0000000000000000 R15: 0000000000000001
>
>
> ---
> 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.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches

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