Re: [syzbot] [rdma?] [s390?] [net?] KASAN: null-ptr-deref Read in smc_tcp_syn_recv_sock

[syzbot <syzbot+827ae2bfb3a3529333e9@syzkaller.appspotmail.com>]

Hello,

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

======================================================
WARNING: possible circular locking dependency detected
6.12.0-rc4-syzkaller-00261-g850925a8133c-dirty #0 Not tainted
------------------------------------------------------
syz.1.6963/21920 is trying to acquire lock:
ffff888033c0b750 ((work_completion)(&new_smc->smc_listen_work)){+.+.}-{0:0}, at: touch_work_lockdep_map kernel/workqueue.c:3895 [inline]
ffff888033c0b750 ((work_completion)(&new_smc->smc_listen_work)){+.+.}-{0:0}, at: start_flush_work kernel/workqueue.c:4149 [inline]
ffff888033c0b750 ((work_completion)(&new_smc->smc_listen_work)){+.+.}-{0:0}, at: __flush_work+0x46d/0xc30 kernel/workqueue.c:4181

but task is already holding lock:
ffff88805fe88dd8 (sk_lock-AF_SMC/1){+.+.}-{0:0}, at: smc_release+0x378/0x5f0 net/smc/af_smc.c:338

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (sk_lock-AF_SMC/1){+.+.}-{0:0}:
       lock_sock_nested+0x3a/0xf0 net/core/sock.c:3611
       smc_listen_out+0x1fa/0x490 net/smc/af_smc.c:1907
       smc_listen_out_connected net/smc/af_smc.c:1927 [inline]
       smc_listen_work+0x571/0x50c0 net/smc/af_smc.c:2441
       process_one_work+0x9c8/0x1ba0 kernel/workqueue.c:3229
       process_scheduled_works kernel/workqueue.c:3310 [inline]
       worker_thread+0x6c8/0xf00 kernel/workqueue.c:3391
       kthread+0x2c4/0x3a0 kernel/kthread.c:389
       ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:147
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

-> #0 ((work_completion)(&new_smc->smc_listen_work)){+.+.}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3161 [inline]
       check_prevs_add kernel/locking/lockdep.c:3280 [inline]
       validate_chain kernel/locking/lockdep.c:3904 [inline]
       __lock_acquire+0x250b/0x3ce0 kernel/locking/lockdep.c:5202
       lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5825
       touch_work_lockdep_map kernel/workqueue.c:3895 [inline]
       start_flush_work kernel/workqueue.c:4149 [inline]
       __flush_work+0x477/0xc30 kernel/workqueue.c:4181
       __cancel_work_sync+0x10c/0x130 kernel/workqueue.c:4337
       smc_clcsock_release+0x5f/0xe0 net/smc/smc_close.c:29
       __smc_release+0x5c2/0x880 net/smc/af_smc.c:303
       smc_close_non_accepted+0xda/0x200 net/smc/af_smc.c:1839
       smc_close_cleanup_listen net/smc/smc_close.c:45 [inline]
       smc_close_active+0xc3c/0x1070 net/smc/smc_close.c:225
       __smc_release+0x634/0x880 net/smc/af_smc.c:279
       smc_release+0x1fc/0x5f0 net/smc/af_smc.c:346
       __sock_release+0xb3/0x270 net/socket.c:658
       sock_close+0x1c/0x30 net/socket.c:1426
       __fput+0x3f9/0xb60 fs/file_table.c:431
       task_work_run+0x151/0x250 kernel/task_work.c:239
       resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
       exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
       exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
       __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
       syscall_exit_to_user_mode+0x27b/0x2a0 kernel/entry/common.c:218
       do_syscall_64+0xda/0x250 arch/x86/entry/common.c:89
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(sk_lock-AF_SMC/1);
                               lock((work_completion)(&new_smc->smc_listen_work));
                               lock(sk_lock-AF_SMC/1);
  lock((work_completion)(&new_smc->smc_listen_work));

 *** DEADLOCK ***

3 locks held by syz.1.6963/21920:
 #0: ffff8880746ea008 (&sb->s_type->i_mutex_key#10){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:815 [inline]
 #0: ffff8880746ea008 (&sb->s_type->i_mutex_key#10){+.+.}-{3:3}, at: __sock_release+0x86/0x270 net/socket.c:657
 #1: ffff88805fe88dd8 (sk_lock-AF_SMC/1){+.+.}-{0:0}, at: smc_release+0x378/0x5f0 net/smc/af_smc.c:338
 #2: ffffffff8e1b8380 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:337 [inline]
 #2: ffffffff8e1b8380 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
 #2: ffffffff8e1b8380 (rcu_read_lock){....}-{1:2}, at: start_flush_work kernel/workqueue.c:4123 [inline]
 #2: ffffffff8e1b8380 (rcu_read_lock){....}-{1:2}, at: __flush_work+0x103/0xc30 kernel/workqueue.c:4181

stack backtrace:
CPU: 0 UID: 0 PID: 21920 Comm: syz.1.6963 Not tainted 6.12.0-rc4-syzkaller-00261-g850925a8133c-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_circular_bug+0x41c/0x610 kernel/locking/lockdep.c:2074
 check_noncircular+0x31a/0x400 kernel/locking/lockdep.c:2206
 check_prev_add kernel/locking/lockdep.c:3161 [inline]
 check_prevs_add kernel/locking/lockdep.c:3280 [inline]
 validate_chain kernel/locking/lockdep.c:3904 [inline]
 __lock_acquire+0x250b/0x3ce0 kernel/locking/lockdep.c:5202
 lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5825
 touch_work_lockdep_map kernel/workqueue.c:3895 [inline]
 start_flush_work kernel/workqueue.c:4149 [inline]
 __flush_work+0x477/0xc30 kernel/workqueue.c:4181
 __cancel_work_sync+0x10c/0x130 kernel/workqueue.c:4337
 smc_clcsock_release+0x5f/0xe0 net/smc/smc_close.c:29
 __smc_release+0x5c2/0x880 net/smc/af_smc.c:303
 smc_close_non_accepted+0xda/0x200 net/smc/af_smc.c:1839
 smc_close_cleanup_listen net/smc/smc_close.c:45 [inline]
 smc_close_active+0xc3c/0x1070 net/smc/smc_close.c:225
 __smc_release+0x634/0x880 net/smc/af_smc.c:279
 smc_release+0x1fc/0x5f0 net/smc/af_smc.c:346
 __sock_release+0xb3/0x270 net/socket.c:658
 sock_close+0x1c/0x30 net/socket.c:1426
 __fput+0x3f9/0xb60 fs/file_table.c:431
 task_work_run+0x151/0x250 kernel/task_work.c:239
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
 exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
 __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
 syscall_exit_to_user_mode+0x27b/0x2a0 kernel/entry/common.c:218
 do_syscall_64+0xda/0x250 arch/x86/entry/common.c:89
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f851fb7e719
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:00007f85208c6038 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007f851fd35f80 RCX: 00007f851fb7e719
RDX: 0000000000000000 RSI: ffffffffffffffff RDI: 0000000000000003
RBP: 00007f851fbf132e R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f851fd35f80 R15: 00007ffea8200be8
 </TASK>


Tested on:

commit:         850925a8 Merge tag '9p-for-6.12-rc5' of https://github..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=114cefb0580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=17c0d505695d6b0
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=155d294c580000