[syzbot] possible deadlock in sk_diag_fill (3)

From: syzbot
Date: Fri Aug 13 2021 - 13:17:24 EST

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Hello,

syzbot found the following issue on:

HEAD commit: 36a21d51725a Linux 5.14-rc5
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=120315e6300000
kernel config: https://syzkaller.appspot.com/x/.config?x=730106bfb5bf8ace
dashboard link: https://syzkaller.appspot.com/bug?extid=00676df89338017efb46
compiler: Debian clang version 11.0.1-2, GNU ld (GNU Binutils for Debian) 2.35.1

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+00676df89338017efb46@xxxxxxxxxxxxxxxxxxxxxxxxx

======================================================
WARNING: possible circular locking dependency detected
5.14.0-rc5-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.5/2925 is trying to acquire lock:
ffff888018d38630 (&u->lock/1){+.+.}-{2:2}, at: sk_diag_dump_icons net/unix/diag.c:86 [inline]
ffff888018d38630 (&u->lock/1){+.+.}-{2:2}, at: sk_diag_fill+0x6f2/0x1090 net/unix/diag.c:154

but task is already holding lock:
ffff888018d389a0 (
rlock-AF_UNIX){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:354 [inline]
rlock-AF_UNIX){+.+.}-{2:2}, at: sk_diag_dump_icons net/unix/diag.c:68 [inline]
rlock-AF_UNIX){+.+.}-{2:2}, at: sk_diag_fill+0x64b/0x1090 net/unix/diag.c:154

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (rlock-AF_UNIX){+.+.}-{2:2}:
lock_acquire+0x182/0x4a0 kernel/locking/lockdep.c:5625
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0xb3/0x100 kernel/locking/spinlock.c:159
skb_queue_tail+0x32/0x120 net/core/skbuff.c:3263
unix_dgram_sendmsg+0x1a3c/0x2a80 net/unix/af_unix.c:1850
sock_sendmsg_nosec net/socket.c:703 [inline]
sock_sendmsg net/socket.c:723 [inline]
____sys_sendmsg+0x5a2/0x900 net/socket.c:2392
___sys_sendmsg net/socket.c:2446 [inline]
__sys_sendmmsg+0x500/0x790 net/socket.c:2532
__do_sys_sendmmsg net/socket.c:2561 [inline]
__se_sys_sendmmsg net/socket.c:2558 [inline]
__x64_sys_sendmmsg+0x9c/0xb0 net/socket.c:2558
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae

-> #0 (&u->lock/1){+.+.}-{2:2}:
check_prev_add kernel/locking/lockdep.c:3051 [inline]
check_prevs_add+0x4f9/0x5b30 kernel/locking/lockdep.c:3174
validate_chain kernel/locking/lockdep.c:3789 [inline]
__lock_acquire+0x4476/0x6100 kernel/locking/lockdep.c:5015
lock_acquire+0x182/0x4a0 kernel/locking/lockdep.c:5625
_raw_spin_lock_nested+0x2d/0x40 kernel/locking/spinlock.c:361
sk_diag_dump_icons net/unix/diag.c:86 [inline]
sk_diag_fill+0x6f2/0x1090 net/unix/diag.c:154
sk_diag_dump net/unix/diag.c:192 [inline]
unix_diag_dump+0x2e9/0x4f0 net/unix/diag.c:220
netlink_dump+0x5b7/0xc30 net/netlink/af_netlink.c:2278
__netlink_dump_start+0x53d/0x710 net/netlink/af_netlink.c:2383
netlink_dump_start include/linux/netlink.h:258 [inline]
unix_diag_handler_dump+0x307/0x7d0 net/unix/diag.c:319
__sock_diag_cmd net/core/sock_diag.c:234 [inline]
sock_diag_rcv_msg+0x350/0x460 net/core/sock_diag.c:265
netlink_rcv_skb+0x1f0/0x460 net/netlink/af_netlink.c:2504
sock_diag_rcv+0x26/0x40 net/core/sock_diag.c:276
netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline]
netlink_unicast+0x7de/0x9b0 net/netlink/af_netlink.c:1340
netlink_sendmsg+0x9e7/0xe00 net/netlink/af_netlink.c:1929
sock_sendmsg_nosec net/socket.c:703 [inline]
sock_sendmsg net/socket.c:723 [inline]
sock_write_iter+0x398/0x520 net/socket.c:1056
do_iter_readv_writev+0x566/0x770 include/linux/fs.h:2108
do_iter_write+0x16c/0x5f0 fs/read_write.c:866
vfs_writev fs/read_write.c:939 [inline]
do_writev+0x240/0x440 fs/read_write.c:982
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae

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 ***

5 locks held by syz-executor.5/2925:
#0: ffffffff8d751a88 (sock_diag_mutex){+.+.}-{3:3}, at: sock_diag_rcv+0x17/0x40 net/core/sock_diag.c:275
#1: ffffffff8d7518e8 (sock_diag_table_mutex){+.+.}-{3:3}, at: __sock_diag_cmd net/core/sock_diag.c:229 [inline]
#1: ffffffff8d7518e8 (sock_diag_table_mutex){+.+.}-{3:3}, at: sock_diag_rcv_msg+0x23f/0x460 net/core/sock_diag.c:265
#2: ffff88806de6f638 (nlk_cb_mutex-SOCK_DIAG){+.+.}-{3:3}, at: netlink_dump+0xd0/0xc30 net/netlink/af_netlink.c:2233
#3: ffffffff8d841178 (unix_table_lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:354 [inline]
#3: ffffffff8d841178 (unix_table_lock){+.+.}-{2:2}, at: unix_diag_dump+0xf1/0x4f0 net/unix/diag.c:206
#4: ffff888018d389a0 (rlock-AF_UNIX){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:354 [inline]
#4: ffff888018d389a0 (rlock-AF_UNIX){+.+.}-{2:2}, at: sk_diag_dump_icons net/unix/diag.c:68 [inline]
#4: ffff888018d389a0 (rlock-AF_UNIX){+.+.}-{2:2}, at: sk_diag_fill+0x64b/0x1090 net/unix/diag.c:154

stack backtrace:
CPU: 0 PID: 2925 Comm: syz-executor.5 Not tainted 5.14.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x1ae/0x29f lib/dump_stack.c:105
print_circular_bug+0xb17/0xdc0 kernel/locking/lockdep.c:2009
check_noncircular+0x2cc/0x390 kernel/locking/lockdep.c:2131
check_prev_add kernel/locking/lockdep.c:3051 [inline]
check_prevs_add+0x4f9/0x5b30 kernel/locking/lockdep.c:3174
validate_chain kernel/locking/lockdep.c:3789 [inline]
__lock_acquire+0x4476/0x6100 kernel/locking/lockdep.c:5015
lock_acquire+0x182/0x4a0 kernel/locking/lockdep.c:5625
_raw_spin_lock_nested+0x2d/0x40 kernel/locking/spinlock.c:361
sk_diag_dump_icons net/unix/diag.c:86 [inline]
sk_diag_fill+0x6f2/0x1090 net/unix/diag.c:154
sk_diag_dump net/unix/diag.c:192 [inline]
unix_diag_dump+0x2e9/0x4f0 net/unix/diag.c:220
netlink_dump+0x5b7/0xc30 net/netlink/af_netlink.c:2278
__netlink_dump_start+0x53d/0x710 net/netlink/af_netlink.c:2383
netlink_dump_start include/linux/netlink.h:258 [inline]
unix_diag_handler_dump+0x307/0x7d0 net/unix/diag.c:319
__sock_diag_cmd net/core/sock_diag.c:234 [inline]
sock_diag_rcv_msg+0x350/0x460 net/core/sock_diag.c:265
netlink_rcv_skb+0x1f0/0x460 net/netlink/af_netlink.c:2504
sock_diag_rcv+0x26/0x40 net/core/sock_diag.c:276
netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline]
netlink_unicast+0x7de/0x9b0 net/netlink/af_netlink.c:1340
netlink_sendmsg+0x9e7/0xe00 net/netlink/af_netlink.c:1929
sock_sendmsg_nosec net/socket.c:703 [inline]
sock_sendmsg net/socket.c:723 [inline]
sock_write_iter+0x398/0x520 net/socket.c:1056
do_iter_readv_writev+0x566/0x770 include/linux/fs.h:2108
do_iter_write+0x16c/0x5f0 fs/read_write.c:866
vfs_writev fs/read_write.c:939 [inline]
do_writev+0x240/0x440 fs/read_write.c:982
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x4665e9
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 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f5b30d9a188 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 000000000056bf80 RCX: 00000000004665e9
RDX: 0000000000000001 RSI: 00000000200000c0 RDI: 0000000000000006
RBP: 00000000004bfcc4 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056bf80
R13: 00007ffd964833ff R14: 00007f5b30d9a300 R15: 0000000000022000

---
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Next message: Rob Herring: "Re: [PATCH v2 1/3] dt-bindings: PCI: ti,j721e: Add bindings to specify legacy interrupts"
Previous message: jim . cromie: "Re: [PATCH v5 2/9] moduleparam: add data member to struct kernel_param"
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