Subject: [syzbot] possible deadlock in sk_diag_fill (4)

From: syzbot <[email-masked]>
Date: Tue, 09 Aug 2022 13:20:22 -0700

Hello,

syzbot found the following issue on:

HEAD commit:    cb71b93c2dc3 Add linux-next specific files for 20220628
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=17f69c12080000
kernel config:  https://syzkaller.appspot.com/x/.config?x=badbc1adb2d582eb
dashboard link: https://syzkaller.appspot.com/bug?extid=ed5155f1684f6cab8abc
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

======================================================
WARNING: possible circular locking dependency detected
5.19.0-rc4-next-20220628-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.3/3509 is trying to acquire lock:
ffff8880765fae70 (&u->lock/1){+.+.}-{2:2}, at: sk_diag_dump_icons net/unix/diag.c:87 [inline]
ffff8880765fae70 (&u->lock/1){+.+.}-{2:2}, at: sk_diag_fill+0xaaf/0x10d0 net/unix/diag.c:155

but task is already holding lock:
ffff8880765fe9e8 (rlock-AF_UNIX){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:360 [inline]
ffff8880765fe9e8 (rlock-AF_UNIX){+.+.}-{2:2}, at: sk_diag_dump_icons net/unix/diag.c:69 [inline]
ffff8880765fe9e8 (rlock-AF_UNIX){+.+.}-{2:2}, at: sk_diag_fill+0x9c3/0x10d0 net/unix/diag.c:155

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (rlock-AF_UNIX){+.+.}-{2:2}:
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0x39/0x50 kernel/locking/spinlock.c:162
       skb_queue_tail+0x21/0x140 net/core/skbuff.c:3371
       unix_dgram_sendmsg+0xf5a/0x1b60 net/unix/af_unix.c:2015
       sock_sendmsg_nosec net/socket.c:714 [inline]
       sock_sendmsg+0xcf/0x120 net/socket.c:734
       io_send+0x26b/0x780 io_uring/net.c:266
       io_issue_sqe+0x15e/0xd20 io_uring/io_uring.c:1601
       io_queue_sqe io_uring/io_uring.c:1778 [inline]
       io_submit_sqe io_uring/io_uring.c:2036 [inline]
       io_submit_sqes+0x9a6/0x1ec0 io_uring/io_uring.c:2147
       __do_sys_io_uring_enter+0xb85/0x1eb0 io_uring/io_uring.c:3087
       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+0x46/0xb0

-> #0 (&u->lock/1){+.+.}-{2:2}:
       check_prev_add kernel/locking/lockdep.c:3095 [inline]
       check_prevs_add kernel/locking/lockdep.c:3214 [inline]
       validate_chain kernel/locking/lockdep.c:3829 [inline]
       __lock_acquire+0x2abe/0x5660 kernel/locking/lockdep.c:5053
       lock_acquire kernel/locking/lockdep.c:5665 [inline]
       lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5630
       _raw_spin_lock_nested+0x30/0x40 kernel/locking/spinlock.c:378
       sk_diag_dump_icons net/unix/diag.c:87 [inline]
       sk_diag_fill+0xaaf/0x10d0 net/unix/diag.c:155
       sk_diag_dump net/unix/diag.c:193 [inline]
       unix_diag_dump+0x3a9/0x640 net/unix/diag.c:217
       netlink_dump+0x541/0xc20 net/netlink/af_netlink.c:2275
       __netlink_dump_start+0x647/0x900 net/netlink/af_netlink.c:2380
       netlink_dump_start include/linux/netlink.h:245 [inline]
       unix_diag_handler_dump net/unix/diag.c:315 [inline]
       unix_diag_handler_dump+0x5c2/0x830 net/unix/diag.c:304
       __sock_diag_cmd net/core/sock_diag.c:235 [inline]
       sock_diag_rcv_msg+0x31a/0x440 net/core/sock_diag.c:266
       netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2501
       sock_diag_rcv+0x26/0x40 net/core/sock_diag.c:277
       netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
       netlink_unicast+0x543/0x7f0 net/netlink/af_netlink.c:1345
       netlink_sendmsg+0x917/0xe10 net/netlink/af_netlink.c:1921
       sock_sendmsg_nosec net/socket.c:714 [inline]
       sock_sendmsg+0xcf/0x120 net/socket.c:734
       sock_no_sendpage+0xff/0x140 net/core/sock.c:3162
       kernel_sendpage.part.0+0x1d5/0x700 net/socket.c:3564
       kernel_sendpage net/socket.c:3561 [inline]
       sock_sendpage+0xdf/0x140 net/socket.c:1054
       pipe_to_sendpage+0x2ad/0x380 fs/splice.c:364
       splice_from_pipe_feed fs/splice.c:418 [inline]
       __splice_from_pipe+0x43e/0x8a0 fs/splice.c:562
       splice_from_pipe fs/splice.c:597 [inline]
       generic_splice_sendpage+0xd4/0x140 fs/splice.c:746
       do_splice_from fs/splice.c:767 [inline]
       do_splice+0xb57/0x1920 fs/splice.c:1079
       __do_splice+0x134/0x250 fs/splice.c:1144
       __do_sys_splice fs/splice.c:1350 [inline]
       __se_sys_splice fs/splice.c:1332 [inline]
       __x64_sys_splice+0x198/0x250 fs/splice.c:1332
       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+0x46/0xb0

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(rlock-AF_UNIX);
                               lock(&u->lock/1);
                               lock(rlock-AF_UNIX);
  lock(&u->lock/1);

 *** DEADLOCK ***

6 locks held by syz-executor.3/3509:
 #0: ffff888074fac468 (&pipe->mutex/1){+.+.}-{3:3}, at: pipe_lock_nested fs/pipe.c:82 [inline]
 #0: ffff888074fac468 (&pipe->mutex/1){+.+.}-{3:3}, at: pipe_lock+0x5a/0x70 fs/pipe.c:90
 #1: ffffffff8d5aef88 (sock_diag_mutex){+.+.}-{3:3}, at: sock_diag_rcv+0x17/0x40 net/core/sock_diag.c:276
 #2: ffffffff8d5af108 (sock_diag_table_mutex){+.+.}-{3:3}, at: __sock_diag_cmd net/core/sock_diag.c:230 [inline]
 #2: ffffffff8d5af108 (sock_diag_table_mutex){+.+.}-{3:3}, at: sock_diag_rcv_msg+0x19b/0x440 net/core/sock_diag.c:266
 #3: ffff88801d907678 (nlk_cb_mutex-SOCK_DIAG){+.+.}-{3:3}, at: netlink_dump+0xae/0xc20 net/netlink/af_netlink.c:2223
 #4: ffff888046a7a798 (&net->unx.table.locks[i]){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:360 [inline]
 #4: ffff888046a7a798 (&net->unx.table.locks[i]){+.+.}-{2:2}, at: unix_diag_dump+0x1b4/0x640 net/unix/diag.c:211
 #5: ffff8880765fe9e8 (rlock-AF_UNIX){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:360 [inline]
 #5: ffff8880765fe9e8 (rlock-AF_UNIX){+.+.}-{2:2}, at: sk_diag_dump_icons net/unix/diag.c:69 [inline]
 #5: ffff8880765fe9e8 (rlock-AF_UNIX){+.+.}-{2:2}, at: sk_diag_fill+0x9c3/0x10d0 net/unix/diag.c:155

stack backtrace:
CPU: 1 PID: 3509 Comm: syz-executor.3 Not tainted 5.19.0-rc4-next-20220628-syzkaller #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
 check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3095 [inline]
 check_prevs_add kernel/locking/lockdep.c:3214 [inline]
 validate_chain kernel/locking/lockdep.c:3829 [inline]
 __lock_acquire+0x2abe/0x5660 kernel/locking/lockdep.c:5053
 lock_acquire kernel/locking/lockdep.c:5665 [inline]
 lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5630
 _raw_spin_lock_nested+0x30/0x40 kernel/locking/spinlock.c:378
 sk_diag_dump_icons net/unix/diag.c:87 [inline]
 sk_diag_fill+0xaaf/0x10d0 net/unix/diag.c:155
 sk_diag_dump net/unix/diag.c:193 [inline]
 unix_diag_dump+0x3a9/0x640 net/unix/diag.c:217
 netlink_dump+0x541/0xc20 net/netlink/af_netlink.c:2275
 __netlink_dump_start+0x647/0x900 net/netlink/af_netlink.c:2380
 netlink_dump_start include/linux/netlink.h:245 [inline]
 unix_diag_handler_dump net/unix/diag.c:315 [inline]
 unix_diag_handler_dump+0x5c2/0x830 net/unix/diag.c:304
 __sock_diag_cmd net/core/sock_diag.c:235 [inline]
 sock_diag_rcv_msg+0x31a/0x440 net/core/sock_diag.c:266
 netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2501
 sock_diag_rcv+0x26/0x40 net/core/sock_diag.c:277
 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
 netlink_unicast+0x543/0x7f0 net/netlink/af_netlink.c:1345
 netlink_sendmsg+0x917/0xe10 net/netlink/af_netlink.c:1921
 sock_sendmsg_nosec net/socket.c:714 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:734
 sock_no_sendpage+0xff/0x140 net/core/sock.c:3162
 kernel_sendpage.part.0+0x1d5/0x700 net/socket.c:3564
 kernel_sendpage net/socket.c:3561 [inline]
 sock_sendpage+0xdf/0x140 net/socket.c:1054
 pipe_to_sendpage+0x2ad/0x380 fs/splice.c:364
 splice_from_pipe_feed fs/splice.c:418 [inline]
 __splice_from_pipe+0x43e/0x8a0 fs/splice.c:562
 splice_from_pipe fs/splice.c:597 [inline]
 generic_splice_sendpage+0xd4/0x140 fs/splice.c:746
 do_splice_from fs/splice.c:767 [inline]
 do_splice+0xb57/0x1920 fs/splice.c:1079
 __do_splice+0x134/0x250 fs/splice.c:1144
 __do_sys_splice fs/splice.c:1350 [inline]
 __se_sys_splice fs/splice.c:1332 [inline]
 __x64_sys_splice+0x198/0x250 fs/splice.c:1332
 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+0x46/0xb0
RIP: 0033:0x7f94a7089209
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f94a8105168 EFLAGS: 00000246 ORIG_RAX: 0000000000000113
RAX: ffffffffffffffda RBX: 00007f94a719bf60 RCX: 00007f94a7089209
RDX: 0000000000000005 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007f94a70e3161 R08: 0000000080000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffd5cb777cf R14: 00007f94a8105300 R15: 0000000000022000
 </TASK>

---
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