Re: [syzbot] [kernfs?] possible deadlock in walk_component (4)

From: syzbot
Date: Sun Feb 02 2025 - 13:56:37 EST

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syzbot has found a reproducer for the following issue on:

HEAD commit: 69e858e0b8b2 Merge tag 'uml-for-linus-6.14-rc1' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10dc6d18580000
kernel config: https://syzkaller.appspot.com/x/.config?x=98d83cc1742b7377
dashboard link: https://syzkaller.appspot.com/bug?extid=b4567a8b2d2ad5f9dd06
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=116fceb0580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15bf03df980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/3d07b0558b0e/disk-69e858e0.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e5e2250eb3b1/vmlinux-69e858e0.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3e676d17effc/bzImage-69e858e0.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b4567a8b2d2ad5f9dd06@xxxxxxxxxxxxxxxxxxxxxxxxx

======================================================
WARNING: possible circular locking dependency detected
6.13.0-syzkaller-09760-g69e858e0b8b2 #0 Not tainted
------------------------------------------------------
syz-executor466/5830 is trying to acquire lock:
ffff88807997f398 (&type->i_mutex_dir_key#6){++++}-{4:4}, at: inode_lock_shared include/linux/fs.h:875 [inline]
ffff88807997f398 (&type->i_mutex_dir_key#6){++++}-{4:4}, at: lookup_slow fs/namei.c:1809 [inline]
ffff88807997f398 (&type->i_mutex_dir_key#6){++++}-{4:4}, at: walk_component+0x342/0x5b0 fs/namei.c:2114

but task is already holding lock:
ffffffff8e07d228 (param_lock){+.+.}-{4:4}, at: kernel_param_lock kernel/params.c:607 [inline]
ffffffff8e07d228 (param_lock){+.+.}-{4:4}, at: param_attr_store+0xe6/0x300 kernel/params.c:586

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #3 (param_lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:585 [inline]
__mutex_lock+0x19b/0xb10 kernel/locking/mutex.c:730
ieee80211_rate_control_ops_get net/mac80211/rate.c:220 [inline]
rate_control_alloc net/mac80211/rate.c:266 [inline]
ieee80211_init_rate_ctrl_alg+0x18d/0x6b0 net/mac80211/rate.c:1015
ieee80211_register_hw+0x2077/0x3ff0 net/mac80211/main.c:1531
mac80211_hwsim_new_radio+0x2c47/0x56d0 drivers/net/wireless/virtual/mac80211_hwsim.c:5558
init_mac80211_hwsim+0x432/0x8c0 drivers/net/wireless/virtual/mac80211_hwsim.c:6910
do_one_initcall+0x128/0x630 init/main.c:1257
do_initcall_level init/main.c:1319 [inline]
do_initcalls init/main.c:1335 [inline]
do_basic_setup init/main.c:1354 [inline]
kernel_init_freeable+0x58f/0x8b0 init/main.c:1568
kernel_init+0x1c/0x2b0 init/main.c:1457
ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

-> #2 (rtnl_mutex){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:585 [inline]
__mutex_lock+0x19b/0xb10 kernel/locking/mutex.c:730
cgrp_css_online+0xa9/0x200 net/core/netprio_cgroup.c:157
online_css+0xaf/0x350 kernel/cgroup/cgroup.c:5568
css_create kernel/cgroup/cgroup.c:5652 [inline]
cgroup_apply_control_enable+0x6d7/0xc80 kernel/cgroup/cgroup.c:3239
cgroup_mkdir+0x398/0x1150 kernel/cgroup/cgroup.c:5847
kernfs_iop_mkdir+0x14a/0x1d0 fs/kernfs/dir.c:1247
vfs_mkdir+0x57d/0x860 fs/namei.c:4313
do_mkdirat+0x301/0x3a0 fs/namei.c:4336
__do_sys_mkdir fs/namei.c:4356 [inline]
__se_sys_mkdir fs/namei.c:4354 [inline]
__x64_sys_mkdir+0xef/0x140 fs/namei.c:4354
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (cgroup_mutex){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:585 [inline]
__mutex_lock+0x19b/0xb10 kernel/locking/mutex.c:730
cgroup_lock include/linux/cgroup.h:368 [inline]
cgroup_kn_lock_live+0x139/0x570 kernel/cgroup/cgroup.c:1662
cgroup_rmdir+0x22/0x2d0 kernel/cgroup/cgroup.c:6045
kernfs_iop_rmdir+0x143/0x1c0 fs/kernfs/dir.c:1265
vfs_rmdir fs/namei.c:4396 [inline]
vfs_rmdir+0x203/0x690 fs/namei.c:4373
do_rmdir+0x3a2/0x410 fs/namei.c:4455
__do_sys_rmdir fs/namei.c:4474 [inline]
__se_sys_rmdir fs/namei.c:4472 [inline]
__x64_sys_rmdir+0xc5/0x110 fs/namei.c:4472
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&type->i_mutex_dir_key#6){++++}-{4:4}:
check_prev_add kernel/locking/lockdep.c:3163 [inline]
check_prevs_add kernel/locking/lockdep.c:3282 [inline]
validate_chain kernel/locking/lockdep.c:3906 [inline]
__lock_acquire+0x249e/0x3c40 kernel/locking/lockdep.c:5228
lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5851
down_read+0x9a/0x330 kernel/locking/rwsem.c:1524
inode_lock_shared include/linux/fs.h:875 [inline]
lookup_slow fs/namei.c:1809 [inline]
walk_component+0x342/0x5b0 fs/namei.c:2114
lookup_last fs/namei.c:2612 [inline]
path_lookupat+0x17f/0x770 fs/namei.c:2636
filename_lookup+0x221/0x5f0 fs/namei.c:2665
kern_path+0x35/0x50 fs/namei.c:2773
lookup_bdev+0xd9/0x280 block/bdev.c:1163
bdev_file_open_by_path+0x83/0x330 block/bdev.c:1036
add_device drivers/mtd/devices/block2mtd.c:279 [inline]
block2mtd_setup2+0x32e/0xe30 drivers/mtd/devices/block2mtd.c:459
block2mtd_setup+0x55/0x70 drivers/mtd/devices/block2mtd.c:476
param_attr_store+0x18f/0x300 kernel/params.c:588
module_attr_store+0x55/0x80 kernel/params.c:924
sysfs_kf_write+0x117/0x170 fs/sysfs/file.c:139
kernfs_fop_write_iter+0x33d/0x500 fs/kernfs/file.c:334
new_sync_write fs/read_write.c:586 [inline]
vfs_write+0x5ae/0x1150 fs/read_write.c:679
ksys_write+0x12b/0x250 fs/read_write.c:731
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
&type->i_mutex_dir_key#6 --> rtnl_mutex --> param_lock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(param_lock);
lock(rtnl_mutex);
lock(param_lock);
rlock(&type->i_mutex_dir_key#6);

*** DEADLOCK ***

4 locks held by syz-executor466/5830:
#0: ffff8880244b2420 (sb_writers#8){.+.+}-{0:0}, at: ksys_write+0x12b/0x250 fs/read_write.c:731
#1: ffff88802975f488 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x27b/0x500 fs/kernfs/file.c:325
#2: ffff88814c9e6008 (kn->active#4){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x29e/0x500 fs/kernfs/file.c:326
#3: ffffffff8e07d228 (param_lock){+.+.}-{4:4}, at: kernel_param_lock kernel/params.c:607 [inline]
#3: ffffffff8e07d228 (param_lock){+.+.}-{4:4}, at: param_attr_store+0xe6/0x300 kernel/params.c:586

stack backtrace:
CPU: 0 UID: 0 PID: 5830 Comm: syz-executor466 Not tainted 6.13.0-syzkaller-09760-g69e858e0b8b2 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
print_circular_bug+0x490/0x760 kernel/locking/lockdep.c:2076
check_noncircular+0x31a/0x400 kernel/locking/lockdep.c:2208
check_prev_add kernel/locking/lockdep.c:3163 [inline]
check_prevs_add kernel/locking/lockdep.c:3282 [inline]
validate_chain kernel/locking/lockdep.c:3906 [inline]
__lock_acquire+0x249e/0x3c40 kernel/locking/lockdep.c:5228
lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5851
down_read+0x9a/0x330 kernel/locking/rwsem.c:1524
inode_lock_shared include/linux/fs.h:875 [inline]
lookup_slow fs/namei.c:1809 [inline]
walk_component+0x342/0x5b0 fs/namei.c:2114
lookup_last fs/namei.c:2612 [inline]
path_lookupat+0x17f/0x770 fs/namei.c:2636
filename_lookup+0x221/0x5f0 fs/namei.c:2665
kern_path+0x35/0x50 fs/namei.c:2773
lookup_bdev+0xd9/0x280 block/bdev.c:1163
bdev_file_open_by_path+0x83/0x330 block/bdev.c:1036
add_device drivers/mtd/devices/block2mtd.c:279 [inline]
block2mtd_setup2+0x32e/0xe30 drivers/mtd/devices/block2mtd.c:459
block2mtd_setup+0x55/0x70 drivers/mtd/devices/block2mtd.c:476
param_attr_store+0x18f/0x300 kernel/params.c:588
module_attr_store+0x55/0x80 kernel/params.c:924
sysfs_kf_write+0x117/0x170 fs/sysfs/file.c:139
kernfs_fop_write_iter+0x33d/0x500 fs/kernfs/file.c:334
new_sync_write fs/read_write.c:586 [inline]
vfs_write+0x5ae/0x1150 fs/read_write.c:679
ksys_write+0x12b/0x250 fs/read_write.c:731
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f64e4ab2ea9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 61 18 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fffc0a6c6d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f64e4ab2ea9
RDX: 0000000000000003 RSI: 0000000020000000 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f64e4afc036
R13: 00007fffc0a6c710 R14: 00007fffc0a6c750 R15: 0000000000000000
</TASK>
block2mtd: error: cannot open device 3QI

---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

Next message: Krzysztof Kozlowski: "Re: [PATCH v5 3/5] arm64: dts: agilex: add dtsi for PCIe Root Port"
Previous message: Danilo Krummrich: "Re: [PATCH 0/4] drm/gpuvm: Add support for single-page-filled mappings"
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