[syzbot] possible deadlock in skb_queue_tail (4)

From: syzbot
Date: Tue Sep 20 2022 - 08:54:40 EST

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Hello,

syzbot found the following issue on:

HEAD commit: 3245cb65fd91 Merge tag 'devicetree-fixes-for-6.0-2' of git..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12b0c487080000
kernel config: https://syzkaller.appspot.com/x/.config?x=98a30118ec9215e9
dashboard link: https://syzkaller.appspot.com/bug?extid=44b38bcb874d81a15a57
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: i386

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: syzbot+44b38bcb874d81a15a57@xxxxxxxxxxxxxxxxxxxxxxxxx

======================================================
WARNING: possible circular locking dependency detected
6.0.0-rc5-syzkaller-00025-g3245cb65fd91 #0 Not tainted
------------------------------------------------------
syz-executor.4/21149 is trying to acquire lock:
ffff8880178441e8 (rlock-AF_UNIX){+.+.}-{2:2}, at: skb_queue_tail+0x21/0x140 net/core/skbuff.c:3400

but task is already holding lock:
ffff888017844670 (&u->lock/1){+.+.}-{2:2}, at: unix_state_double_lock net/unix/af_unix.c:1298 [inline]
ffff888017844670 (&u->lock/1){+.+.}-{2:2}, at: unix_state_double_lock+0x77/0xa0 net/unix/af_unix.c:1290

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&u->lock/1){+.+.}-{2:2}:
_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_write_iter+0x291/0x3d0 net/socket.c:1108
call_write_iter include/linux/fs.h:2187 [inline]
do_iter_readv_writev+0x20b/0x3b0 fs/read_write.c:729
do_iter_write+0x182/0x700 fs/read_write.c:855
vfs_writev+0x1aa/0x630 fs/read_write.c:928
do_writev+0x279/0x2f0 fs/read_write.c:971
do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline]
__do_fast_syscall_32+0x65/0xf0 arch/x86/entry/common.c:178
do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:203
entry_SYSENTER_compat_after_hwframe+0x70/0x82

-> #0 (rlock-AF_UNIX){+.+.}-{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+0x2a43/0x56d0 kernel/locking/lockdep.c:5053
lock_acquire kernel/locking/lockdep.c:5666 [inline]
lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5631
__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:3400
unix_dgram_sendmsg+0xf41/0x1b50 net/unix/af_unix.c:2043
sock_sendmsg_nosec net/socket.c:714 [inline]
sock_sendmsg+0xcf/0x120 net/socket.c:734
____sys_sendmsg+0x6eb/0x810 net/socket.c:2482
__sys_sendmsg_sock+0x26/0x30 net/socket.c:2548
io_sendmsg+0x246/0x7d0 io_uring/net.c:289
io_issue_sqe+0x6b6/0xd20 io_uring/io_uring.c:1577
io_queue_sqe io_uring/io_uring.c:1755 [inline]
io_submit_sqe io_uring/io_uring.c:2013 [inline]
io_submit_sqes+0x94e/0x1d30 io_uring/io_uring.c:2124
__do_sys_io_uring_enter+0xb85/0x1ea0 io_uring/io_uring.c:3054
do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline]
__do_fast_syscall_32+0x65/0xf0 arch/x86/entry/common.c:178
do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:203
entry_SYSENTER_compat_after_hwframe+0x70/0x82

other info that might help us debug this:

Possible unsafe locking scenario:

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

*** DEADLOCK ***

2 locks held by syz-executor.4/21149:
#0: ffff88807dcb40a8 (&ctx->uring_lock){+.+.}-{3:3}, at: __do_sys_io_uring_enter+0xb7a/0x1ea0 io_uring/io_uring.c:3053
#1: ffff888017844670 (&u->lock/1){+.+.}-{2:2}, at: unix_state_double_lock net/unix/af_unix.c:1298 [inline]
#1: ffff888017844670 (&u->lock/1){+.+.}-{2:2}, at: unix_state_double_lock+0x77/0xa0 net/unix/af_unix.c:1290

stack backtrace:
CPU: 0 PID: 21149 Comm: syz-executor.4 Not tainted 6.0.0-rc5-syzkaller-00025-g3245cb65fd91 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2022
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+0x2a43/0x56d0 kernel/locking/lockdep.c:5053
lock_acquire kernel/locking/lockdep.c:5666 [inline]
lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5631
__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:3400
unix_dgram_sendmsg+0xf41/0x1b50 net/unix/af_unix.c:2043
sock_sendmsg_nosec net/socket.c:714 [inline]
sock_sendmsg+0xcf/0x120 net/socket.c:734
____sys_sendmsg+0x6eb/0x810 net/socket.c:2482
__sys_sendmsg_sock+0x26/0x30 net/socket.c:2548
io_sendmsg+0x246/0x7d0 io_uring/net.c:289
io_issue_sqe+0x6b6/0xd20 io_uring/io_uring.c:1577
io_queue_sqe io_uring/io_uring.c:1755 [inline]
io_submit_sqe io_uring/io_uring.c:2013 [inline]
io_submit_sqes+0x94e/0x1d30 io_uring/io_uring.c:2124
__do_sys_io_uring_enter+0xb85/0x1ea0 io_uring/io_uring.c:3054
do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline]
__do_fast_syscall_32+0x65/0xf0 arch/x86/entry/common.c:178
do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:203
entry_SYSENTER_compat_after_hwframe+0x70/0x82
RIP: 0023:0xf7faf549
Code: 03 74 c0 01 10 05 03 74 b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 8d b4 26 00 00 00 00 8d b4 26 00 00 00 00
RSP: 002b:00000000f7f895cc EFLAGS: 00000296 ORIG_RAX: 00000000000001aa
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000002a6e
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
</TASK>
----------------
Code disassembly (best guess):
0: 03 74 c0 01 add 0x1(%rax,%rax,8),%esi
4: 10 05 03 74 b8 01 adc %al,0x1b87403(%rip) # 0x1b8740d
a: 10 06 adc %al,(%rsi)
c: 03 74 b4 01 add 0x1(%rsp,%rsi,4),%esi
10: 10 07 adc %al,(%rdi)
12: 03 74 b0 01 add 0x1(%rax,%rsi,4),%esi
16: 10 08 adc %cl,(%rax)
18: 03 74 d8 01 add 0x1(%rax,%rbx,8),%esi
1c: 00 00 add %al,(%rax)
1e: 00 00 add %al,(%rax)
20: 00 51 52 add %dl,0x52(%rcx)
23: 55 push %rbp
24: 89 e5 mov %esp,%ebp
26: 0f 34 sysenter
28: cd 80 int $0x80
* 2a: 5d pop %rbp <-- trapping instruction
2b: 5a pop %rdx
2c: 59 pop %rcx
2d: c3 retq
2e: 90 nop
2f: 90 nop
30: 90 nop
31: 90 nop
32: 8d b4 26 00 00 00 00 lea 0x0(%rsi,%riz,1),%esi
39: 8d b4 26 00 00 00 00 lea 0x0(%rsi,%riz,1),%esi

---
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Next message: Christian König: "Re: [PATCH] drm/amdgpu: initialize r variable into amdgpu_cs_submit function"
Previous message: Maxime Ripard: "[PATCH v2 1/7] firmware: raspberrypi: Introduce rpi_firmware_find_node()"
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