af_unix: fix lockdep positive in sk_diag_dump_icons()
syzbot reported a lockdep splat [1].
Blamed commit hinted about the possible lockdep
violation, and code used unix_state_lock_nested()
in an attempt to silence lockdep.
It is not sufficient, because unix_state_lock_nested()
is already used from unix_state_double_lock().
We need to use a separate subclass.
This patch adds a distinct enumeration to make things
more explicit.
Also use swap() in unix_state_double_lock() as a clean up.
v2: add a missing inline keyword to unix_state_lock_nested()
[1]
WARNING: possible circular locking dependency detected
6.8.0-rc1-syzkaller-00356-g8a696a29c690 #0 Not tainted
syz-executor.1/2542 is trying to acquire lock:
ffff88808b5df9e8 (rlock-AF_UNIX){+.+.}-{2:2}, at: skb_queue_tail+0x36/0x120 net/core/skbuff.c:3863
but task is already holding lock:
ffff88808b5dfe70 (&u->lock/1){+.+.}-{2:2}, at: unix_dgram_sendmsg+0xfc7/0x2200 net/unix/af_unix.c:2089
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&u->lock/1){+.+.}-{2:2}:
lock_acquire+0x1e3/0x530 kernel/locking/lockdep.c:5754
_raw_spin_lock_nested+0x31/0x40 kernel/locking/spinlock.c:378
sk_diag_dump_icons net/unix/diag.c:87 [inline]
sk_diag_fill+0x6ea/0xfe0 net/unix/diag.c:157
sk_diag_dump net/unix/diag.c:196 [inline]
unix_diag_dump+0x3e9/0x630 net/unix/diag.c:220
netlink_dump+0x5c1/0xcd0 net/netlink/af_netlink.c:2264
__netlink_dump_start+0x5d7/0x780 net/netlink/af_netlink.c:2370
netlink_dump_start include/linux/netlink.h:338 [inline]
unix_diag_handler_dump+0x1c3/0x8f0 net/unix/diag.c:319
sock_diag_rcv_msg+0xe3/0x400
netlink_rcv_skb+0x1df/0x430 net/netlink/af_netlink.c:2543
sock_diag_rcv+0x2a/0x40 net/core/sock_diag.c:280
netlink_unicast_kernel net/netlink/af_netlink.c:1341 [inline]
netlink_unicast+0x7e6/0x980 net/netlink/af_netlink.c:1367
netlink_sendmsg+0xa37/0xd70 net/netlink/af_netlink.c:1908
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg net/socket.c:745 [inline]
sock_write_iter+0x39a/0x520 net/socket.c:1160
call_write_iter include/linux/fs.h:2085 [inline]
new_sync_write fs/read_write.c:497 [inline]
vfs_write+0xa74/0xca0 fs/read_write.c:590
ksys_write+0x1a0/0x2c0 fs/read_write.c:643
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf5/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b
-> #0 (rlock-AF_UNIX){+.+.}-{2:2}:
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain+0x1909/0x5ab0 kernel/locking/lockdep.c:3869
__lock_acquire+0x1345/0x1fd0 kernel/locking/lockdep.c:5137
lock_acquire+0x1e3/0x530 kernel/locking/lockdep.c:5754
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0xd5/0x120 kernel/locking/spinlock.c:162
skb_queue_tail+0x36/0x120 net/core/skbuff.c:3863
unix_dgram_sendmsg+0x15d9/0x2200 net/unix/af_unix.c:2112
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg net/socket.c:745 [inline]
____sys_sendmsg+0x592/0x890 net/socket.c:2584
___sys_sendmsg net/socket.c:2638 [inline]
__sys_sendmmsg+0x3b2/0x730 net/socket.c:2724
__do_sys_sendmmsg net/socket.c:2753 [inline]
__se_sys_sendmmsg net/socket.c:2750 [inline]
__x64_sys_sendmmsg+0xa0/0xb0 net/socket.c:2750
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf5/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b
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 ***
1 lock held by syz-executor.1/2542:
#0: ffff88808b5dfe70 (&u->lock/1){+.+.}-{2:2}, at: unix_dgram_sendmsg+0xfc7/0x2200 net/unix/af_unix.c:2089
stack backtrace:
CPU: 1 PID: 2542 Comm: syz-executor.1 Not tainted 6.8.0-rc1-syzkaller-00356-g8a696a29c690 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x1e7/0x2d0 lib/dump_stack.c:106
check_noncircular+0x366/0x490 kernel/locking/lockdep.c:2187
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain+0x1909/0x5ab0 kernel/locking/lockdep.c:3869
__lock_acquire+0x1345/0x1fd0 kernel/locking/lockdep.c:5137
lock_acquire+0x1e3/0x530 kernel/locking/lockdep.c:5754
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0xd5/0x120 kernel/locking/spinlock.c:162
skb_queue_tail+0x36/0x120 net/core/skbuff.c:3863
unix_dgram_sendmsg+0x15d9/0x2200 net/unix/af_unix.c:2112
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg net/socket.c:745 [inline]
____sys_sendmsg+0x592/0x890 net/socket.c:2584
___sys_sendmsg net/socket.c:2638 [inline]
__sys_sendmmsg+0x3b2/0x730 net/socket.c:2724
__do_sys_sendmmsg net/socket.c:2753 [inline]
__se_sys_sendmmsg net/socket.c:2750 [inline]
__x64_sys_sendmmsg+0xa0/0xb0 net/socket.c:2750
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf5/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b
RIP: 0033:0x7f26d887cda9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 20 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f26d95a60c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00007f26d89abf80 RCX: 00007f26d887cda9
RDX: 000000000000003e RSI: 00000000200bd000 RDI: 0000000000000004
RBP: 00007f26d88c947a R08: 0000000000000000 R09: 0000000000000000
R10: 00000000000008c0 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007f26d89abf80 R15: 00007ffcfe081a68
Fixes: 2aac7a2c ("unix_diag: Pending connections IDs NLA")
Reported-by: 
syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20240130184235.1620738-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>