Re: [syzbot] [smc?] KASAN: null-ptr-deref Read in smc_tcp_syn_recv_sock

syzbot
2025-06-29T16:00:04Z

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
possible deadlock in inet_child_forget

======================================================
WARNING: possible circular locking dependency detected
6.16.0-rc3-syzkaller-gdfba48a70cb6-dirty #0 Not tainted
------------------------------------------------------
syz.2.23/6591 is trying to acquire lock:
ffff88805b87ac70 (k-clock-AF_INET6){++.-}-{3:3}, at: sock_orphan include/net/sock.h:2075 [inline]
ffff88805b87ac70 (k-clock-AF_INET6){++.-}-{3:3}, at: inet_child_forget+0x7e/0x2e0 net/ipv4/inet_connection_sock.c:1383

but task is already holding lock:
ffff88805b87aa58 (k-slock-AF_INET6){+.-.}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffff88805b87aa58 (k-slock-AF_INET6){+.-.}-{3:3}, at: inet_csk_listen_stop+0x203/0x1090 net/ipv4/inet_connection_sock.c:1495

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (k-slock-AF_INET6){+.-.}-{3:3}:
__raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
_raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
spin_lock include/linux/spinlock.h:351 [inline]
sk_clone_lock+0x334/0x1330 net/core/sock.c:2499
inet_csk_clone_lock+0x2a/0x750 net/ipv4/inet_connection_sock.c:1232
tcp_create_openreq_child+0x34/0x1980 net/ipv4/tcp_minisocks.c:526
tcp_v4_syn_recv_sock+0x115/0x1250 net/ipv4/tcp_ipv4.c:1774
tcp_v6_syn_recv_sock+0x1353/0x2480 net/ipv6/tcp_ipv6.c:1382
smc_tcp_syn_recv_sock+0x24b/0x500 net/smc/af_smc.c:144
tcp_check_req+0x69d/0x1f80 net/ipv4/tcp_minisocks.c:874
tcp_v4_rcv+0x19b0/0x4650 net/ipv4/tcp_ipv4.c:2283
ip_protocol_deliver_rcu+0xba/0x4c0 net/ipv4/ip_input.c:205
ip_local_deliver_finish+0x316/0x570 net/ipv4/ip_input.c:233
NF_HOOK include/linux/netfilter.h:317 [inline]
NF_HOOK include/linux/netfilter.h:311 [inline]
ip_local_deliver+0x18e/0x1f0 net/ipv4/ip_input.c:254
dst_input include/net/dst.h:469 [inline]
ip_rcv_finish net/ipv4/ip_input.c:447 [inline]
NF_HOOK include/linux/netfilter.h:317 [inline]
NF_HOOK include/linux/netfilter.h:311 [inline]
ip_rcv+0x2c3/0x5d0 net/ipv4/ip_input.c:567
__netif_receive_skb_one_core+0x197/0x1e0 net/core/dev.c:5977
__netif_receive_skb+0x1d/0x160 net/core/dev.c:6090
process_backlog+0x442/0x15e0 net/core/dev.c:6442
__napi_poll.constprop.0+0xba/0x550 net/core/dev.c:7414
napi_poll net/core/dev.c:7478 [inline]
net_rx_action+0xa9f/0xfe0 net/core/dev.c:7605
handle_softirqs+0x219/0x8e0 kernel/softirq.c:579
do_softirq kernel/softirq.c:480 [inline]
do_softirq+0xb2/0xf0 kernel/softirq.c:467
__local_bh_enable_ip+0x100/0x120 kernel/softirq.c:407
local_bh_enable include/linux/bottom_half.h:33 [inline]
rcu_read_unlock_bh include/linux/rcupdate.h:910 [inline]
__dev_queue_xmit+0x8ab/0x43e0 net/core/dev.c:4740
dev_queue_xmit include/linux/netdevice.h:3355 [inline]
neigh_hh_output include/net/neighbour.h:523 [inline]
neigh_output include/net/neighbour.h:537 [inline]
ip_finish_output2+0xc38/0x21a0 net/ipv4/ip_output.c:235
__ip_finish_output net/ipv4/ip_output.c:313 [inline]
__ip_finish_output+0x49e/0x950 net/ipv4/ip_output.c:295
ip_finish_output+0x35/0x380 net/ipv4/ip_output.c:323
NF_HOOK_COND include/linux/netfilter.h:306 [inline]
ip_output+0x13b/0x2a0 net/ipv4/ip_output.c:433
dst_output include/net/dst.h:459 [inline]
ip_local_out net/ipv4/ip_output.c:129 [inline]
__ip_queue_xmit+0x1d7d/0x26c0 net/ipv4/ip_output.c:527
__tcp_transmit_skb+0x2686/0x3e90 net/ipv4/tcp_output.c:1479
__tcp_send_ack.part.0+0x3de/0x700 net/ipv4/tcp_output.c:4279
__tcp_send_ack net/ipv4/tcp_output.c:4285 [inline]
tcp_send_ack+0x84/0xa0 net/ipv4/tcp_output.c:4285
tcp_rcv_synsent_state_process net/ipv4/tcp_input.c:6632 [inline]
tcp_rcv_state_process+0x4236/0x4ed0 net/ipv4/tcp_input.c:6826
tcp_v4_do_rcv+0x1ad/0xa90 net/ipv4/tcp_ipv4.c:1948
sk_backlog_rcv include/net/sock.h:1148 [inline]
__release_sock+0x31b/0x400 net/core/sock.c:3213
release_sock+0x5a/0x220 net/core/sock.c:3767
mptcp_connect+0xccd/0xfe0 net/mptcp/protocol.c:3695
__inet_stream_connect+0x3c8/0x1020 net/ipv4/af_inet.c:677
inet_stream_connect+0x57/0xa0 net/ipv4/af_inet.c:748
__sys_connect_file+0x141/0x1a0 net/socket.c:2038
__sys_connect+0x13b/0x160 net/socket.c:2057
__do_sys_connect net/socket.c:2063 [inline]
__se_sys_connect net/socket.c:2060 [inline]
__x64_sys_connect+0x72/0xb0 net/socket.c:2060
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (k-clock-AF_INET6){++.-}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3168 [inline]
check_prevs_add kernel/locking/lockdep.c:3287 [inline]
validate_chain kernel/locking/lockdep.c:3911 [inline]
__lock_acquire+0x126f/0x1c90 kernel/locking/lockdep.c:5240
lock_acquire kernel/locking/lockdep.c:5871 [inline]
lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5828
__raw_write_lock_bh include/linux/rwlock_api_smp.h:202 [inline]
_raw_write_lock_bh+0x33/0x40 kernel/locking/spinlock.c:334
sock_orphan include/net/sock.h:2075 [inline]
inet_child_forget+0x7e/0x2e0 net/ipv4/inet_connection_sock.c:1383
inet_csk_listen_stop+0x323/0x1090 net/ipv4/inet_connection_sock.c:1523
tcp_disconnect+0x18a4/0x1ec0 net/ipv4/tcp.c:3340
inet_shutdown+0x26f/0x440 net/ipv4/af_inet.c:935
smc_close_active+0xc2a/0x1070 net/smc/smc_close.c:223
__smc_release+0x634/0x880 net/smc/af_smc.c:282
smc_release+0x1fc/0x5f0 net/smc/af_smc.c:349
__sock_release+0xb3/0x270 net/socket.c:647
sock_close+0x1c/0x30 net/socket.c:1391
__fput+0x402/0xb70 fs/file_table.c:465
task_work_run+0x150/0x240 kernel/task_work.c:227
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
exit_to_user_mode_loop+0xeb/0x110 kernel/entry/common.c:114
exit_to_user_mode_prepare include/linux/entry-common.h:330 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:414 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:449 [inline]
do_syscall_64+0x3f6/0x4c0 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(k-slock-AF_INET6);
lock(k-clock-AF_INET6);
lock(k-slock-AF_INET6);
lock(k-clock-AF_INET6);

*** DEADLOCK ***

4 locks held by syz.2.23/6591:
#0: ffff88805b065608 (&sb->s_type->i_mutex_key#11){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:869 [inline]
#0: ffff88805b065608 (&sb->s_type->i_mutex_key#11){+.+.}-{4:4}, at: __sock_release+0x86/0x270 net/socket.c:646
#1: ffff888058b0a4d8 (sk_lock-AF_SMC/1){+.+.}-{0:0}, at: smc_release+0x378/0x5f0 net/smc/af_smc.c:341
#2: ffff88805b878fd8 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1667 [inline]
#2: ffff88805b878fd8 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: inet_shutdown+0x67/0x440 net/ipv4/af_inet.c:905
#3: ffff88805b87aa58 (k-slock-AF_INET6){+.-.}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline]
#3: ffff88805b87aa58 (k-slock-AF_INET6){+.-.}-{3:3}, at: inet_csk_listen_stop+0x203/0x1090 net/ipv4/inet_connection_sock.c:1495

stack backtrace:
CPU: 0 UID: 0 PID: 6591 Comm: syz.2.23 Not tainted 6.16.0-rc3-syzkaller-gdfba48a70cb6-dirty #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
print_circular_bug+0x275/0x350 kernel/locking/lockdep.c:2046
check_noncircular+0x14c/0x170 kernel/locking/lockdep.c:2178
check_prev_add kernel/locking/lockdep.c:3168 [inline]
check_prevs_add kernel/locking/lockdep.c:3287 [inline]
validate_chain kernel/locking/lockdep.c:3911 [inline]
__lock_acquire+0x126f/0x1c90 kernel/locking/lockdep.c:5240
lock_acquire kernel/locking/lockdep.c:5871 [inline]
lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5828
__raw_write_lock_bh include/linux/rwlock_api_smp.h:202 [inline]
_raw_write_lock_bh+0x33/0x40 kernel/locking/spinlock.c:334
sock_orphan include/net/sock.h:2075 [inline]
inet_child_forget+0x7e/0x2e0 net/ipv4/inet_connection_sock.c:1383
inet_csk_listen_stop+0x323/0x1090 net/ipv4/inet_connection_sock.c:1523
tcp_disconnect+0x18a4/0x1ec0 net/ipv4/tcp.c:3340
inet_shutdown+0x26f/0x440 net/ipv4/af_inet.c:935
smc_close_active+0xc2a/0x1070 net/smc/smc_close.c:223
__smc_release+0x634/0x880 net/smc/af_smc.c:282
smc_release+0x1fc/0x5f0 net/smc/af_smc.c:349
__sock_release+0xb3/0x270 net/socket.c:647
sock_close+0x1c/0x30 net/socket.c:1391
__fput+0x402/0xb70 fs/file_table.c:465
task_work_run+0x150/0x240 kernel/task_work.c:227
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
exit_to_user_mode_loop+0xeb/0x110 kernel/entry/common.c:114
exit_to_user_mode_prepare include/linux/entry-common.h:330 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:414 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:449 [inline]
do_syscall_64+0x3f6/0x4c0 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fec9fd7e719
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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fec9effe038 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007fec9ff35f80 RCX: 00007fec9fd7e719
RDX: 0000000000000000 RSI: ffffffffffffffff RDI: 0000000000000003
RBP: 00007fec9fdf132e R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007fec9ff35f80 R15: 00007ffd574ead88
</TASK>

Tested on:

commit: dfba48a7 Merge tag 'i2c-for-6.16-rc4' of git://git.ker..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11cd688c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=d3e0d55231e0c89c
dashboard link: https://syzkaller.appspot.com/bug?extid=827ae2bfb3a3529333e9
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
patch: https://syzkaller.appspot.com/x/patch.diff?x=10e2a982580000