Re: [syzbot] [fs?] KASAN: slab-use-after-free Read in debugfs_u32_get (2)

[syzbot <syzbot+6c25f4750230faf70be9@syzkaller.appspotmail.com>]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

[   90.657969][   T12] netdevsim netdevsim1 netdevsim2: set [1, 0] type 2 family 0 port 6081 - 0
[   90.667366][   T12] netdevsim netdevsim1 netdevsim3: set [1, 0] type 2 family 0 port 6081 - 0
2026/06/18 09:21:13 executed programs: 0
[   90.770444][   T50] Bluetooth: hci0: unexpected cc 0x0c03 length: 249 > 1
[   90.781106][   T50] Bluetooth: hci0: unexpected cc 0x1003 length: 249 > 9
[   90.792650][   T50] Bluetooth: hci0: unexpected cc 0x1001 length: 249 > 9
[   90.802067][   T50] Bluetooth: hci0: unexpected cc 0x0c23 length: 249 > 4
[   90.809763][   T50] Bluetooth: hci0: unexpected cc 0x0c38 length: 249 > 2
[   91.161772][ T5757] bridge0: port 1(bridge_slave_0) entered blocking state
[   91.169484][ T5757] bridge0: port 1(bridge_slave_0) entered disabled state
[   91.177477][ T5757] bridge_slave_0: entered allmulticast mode
[   91.185001][ T5757] bridge_slave_0: entered promiscuous mode
[   91.193706][ T5757] bridge0: port 2(bridge_slave_1) entered blocking state
[   91.201868][ T5757] bridge0: port 2(bridge_slave_1) entered disabled state
[   91.209601][ T5757] bridge_slave_1: entered allmulticast mode
[   91.217118][ T5757] bridge_slave_1: entered promiscuous mode
[   91.238425][ T5757] bond0: (slave bond_slave_0): Enslaving as an active interface with an up link
[   91.250819][ T5757] bond0: (slave bond_slave_1): Enslaving as an active interface with an up link
[   91.276001][ T5757] team0: Port device team_slave_0 added
[   91.283694][ T5757] team0: Port device team_slave_1 added
[   91.302541][ T5757] batman_adv: batadv0: Adding interface: batadv_slave_0
[   91.309669][ T5757] batman_adv: batadv0: The MTU of interface batadv_slave_0 is too small (1500) to handle the transport of batman-adv packets. Packets going over this interface will be fragmented on layer2 which could impact the performance. Setting the MTU to 1532 would solve the problem.
[   91.336872][ T5757] batman_adv: batadv0: Not using interface batadv_slave_0 (retrying later): interface not active
[   91.349188][ T5757] batman_adv: batadv0: Adding interface: batadv_slave_1
[   91.357166][ T5757] batman_adv: batadv0: The MTU of interface batadv_slave_1 is too small (1500) to handle the transport of batman-adv packets. Packets going over this interface will be fragmented on layer2 which could impact the performance. Setting the MTU to 1532 would solve the problem.
[   91.384019][ T5757] batman_adv: batadv0: Not using interface batadv_slave_1 (retrying later): interface not active
[   91.420336][ T5757] hsr_slave_0: entered promiscuous mode
[   91.427350][ T5757] hsr_slave_1: entered promiscuous mode
[   91.433876][ T5757] debugfs: 'hsr0' already exists in 'hsr'
[   91.439785][ T5757] Cannot create hsr debugfs directory
[   91.532434][ T5757] netdevsim netdevsim0 netdevsim0: renamed from eth0
[   91.541647][ T5757] 8021q: adding VLAN 0 to HW filter on device netdevsim0
[   91.550200][ T5757] netdevsim netdevsim0 netdevsim1: renamed from eth1
[   91.559463][ T5757] 8021q: adding VLAN 0 to HW filter on device netdevsim1
[   91.569779][ T5757] netdevsim netdevsim0 netdevsim2: renamed from eth2
[   91.579911][ T5757] 8021q: adding VLAN 0 to HW filter on device netdevsim2
[   91.588284][ T5757] netdevsim netdevsim0 netdevsim3: renamed from eth3
[   91.597422][ T5757] 8021q: adding VLAN 0 to HW filter on device netdevsim3
[   91.618154][ T5757] bridge0: port 2(bridge_slave_1) entered blocking state
[   91.625451][ T5757] bridge0: port 2(bridge_slave_1) entered forwarding state
[   91.633183][ T5757] bridge0: port 1(bridge_slave_0) entered blocking state
[   91.640456][ T5757] bridge0: port 1(bridge_slave_0) entered forwarding state
[   91.651809][   T58] bridge0: port 1(bridge_slave_0) entered disabled state
[   91.659706][   T58] bridge0: port 2(bridge_slave_1) entered disabled state
[   91.705781][ T5757] 8021q: adding VLAN 0 to HW filter on device bond0
[   91.724491][ T5757] 8021q: adding VLAN 0 to HW filter on device team0
[   91.736217][   T58] bridge0: port 1(bridge_slave_0) entered blocking state
[   91.743525][   T58] bridge0: port 1(bridge_slave_0) entered forwarding state
[   91.758884][   T58] bridge0: port 2(bridge_slave_1) entered blocking state
[   91.766069][   T58] bridge0: port 2(bridge_slave_1) entered forwarding state
[   92.054180][ T5757] 8021q: adding VLAN 0 to HW filter on device batadv0
[   92.094726][ T5757] veth0_vlan: entered promiscuous mode
[   92.105045][ T5757] veth1_vlan: entered promiscuous mode
[   92.132923][ T5757] veth0_macvtap: entered promiscuous mode
[   92.143175][ T5757] veth1_macvtap: entered promiscuous mode
[   92.158019][ T5757] batman_adv: batadv0: Interface activated: batadv_slave_0
[   92.171480][ T5757] batman_adv: batadv0: Interface activated: batadv_slave_1
[   92.185832][   T12] netdevsim netdevsim0 netdevsim0: set [1, 0] type 2 family 0 port 6081 - 0
[   92.198478][   T12] netdevsim netdevsim0 netdevsim1: set [1, 0] type 2 family 0 port 6081 - 0
[   92.207627][   T12] netdevsim netdevsim0 netdevsim2: set [1, 0] type 2 family 0 port 6081 - 0
[   92.217684][   T12] netdevsim netdevsim0 netdevsim3: set [1, 0] type 2 family 0 port 6081 - 0
[   92.260657][   T12] wlan0: Created IBSS using preconfigured BSSID 50:50:50:50:50:50
[   92.271752][   T12] wlan0: Creating new IBSS network, BSSID 50:50:50:50:50:50
[   92.292048][   T12] wlan1: Created IBSS using preconfigured BSSID 50:50:50:50:50:50
[   92.300386][   T12] wlan1: Creating new IBSS network, BSSID 50:50:50:50:50:50
[   92.434520][   T36] ==================================================================
[   92.443019][   T36] BUG: KASAN: null-ptr-deref in down_write_nested+0xb4/0x200
[   92.451123][   T36] Write of size 8 at addr 00000000000000d8 by task kworker/u8:2/36
[   92.459336][   T36] 
[   92.461731][   T36] CPU: 0 UID: 0 PID: 36 Comm: kworker/u8:2 Not tainted syzkaller #0 PREEMPT(full) 
[   92.461766][   T36] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
[   92.461789][   T36] Workqueue: netns cleanup_net
[   92.461838][   T36] Call Trace:
[   92.461849][   T36]  <TASK>
[   92.461860][   T36]  dump_stack_lvl+0x100/0x190
[   92.461910][   T36]  kasan_report+0xdf/0x1c0
[   92.461955][   T36]  ? down_write_nested+0xb4/0x200
[   92.462001][   T36]  kasan_check_range+0x10f/0x1e0
[   92.462031][   T36]  down_write_nested+0xb4/0x200
[   92.462071][   T36]  ? __simple_recursive_removal+0x7f/0x5c0
[   92.462115][   T36]  ? __pfx_down_write_nested+0x10/0x10
[   92.462157][   T36]  ? lock_release+0x24d/0x310
[   92.462193][   T36]  ? do_raw_spin_unlock+0x145/0x1e0
[   92.462235][   T36]  __simple_recursive_removal+0x7f/0x5c0
[   92.462279][   T36]  ? __pfx_remove_one+0x10/0x10
[   92.462319][   T36]  ? mntput+0x70/0xa0
[   92.462360][   T36]  debugfs_remove+0x5d/0x80
[   92.462397][   T36]  nsim_destroy+0x6a/0x970
[   92.462434][   T36]  ? mntput_no_expire+0x202/0x220
[   92.462477][   T36]  __nsim_dev_port_del+0x1c2/0x2b0
[   92.462520][   T36]  nsim_dev_reload_destroy+0x10a/0x4a0
[   92.462545][   T36]  ? xa_get_mark+0x19c/0x750
[   92.462570][   T36]  ? lock_release+0x24d/0x310
[   92.462606][   T36]  nsim_dev_reload_down+0x66/0xd0
[   92.462631][   T36]  devlink_reload+0x1ae/0x7a0
[   92.462659][   T36]  ? __pfx_devlink_reload+0x10/0x10
[   92.462691][   T36]  devlink_pernet_pre_exit+0x247/0x370
[   92.462730][   T36]  ? iput.part.0+0x1a0/0x1050
[   92.462762][   T36]  ? __pfx_devlink_pernet_pre_exit+0x10/0x10
[   92.462846][   T36]  ? iput+0x3a/0x40
[   92.462875][   T36]  ? sock_release+0x14d/0x1c0
[   92.462910][   T36]  ? __pfx_devlink_pernet_pre_exit+0x10/0x10
[   92.462950][   T36]  ops_undo_list+0x187/0xab0
[   92.462981][   T36]  ? __pfx_ops_undo_list+0x10/0x10
[   92.463009][   T36]  ? rcu_is_watching+0x12/0xc0
[   92.463073][   T36]  ? cleanup_net+0x332/0x920
[   92.463102][   T36]  ? lock_release+0x24d/0x310
[   92.463136][   T36]  ? idr_destroy+0x62/0x2e0
[   92.463167][   T36]  cleanup_net+0x499/0x920
[   92.463199][   T36]  ? __pfx_cleanup_net+0x10/0x10
[   92.463228][   T36]  ? rcu_is_watching+0x12/0xc0
[   92.463253][   T36]  ? lock_acquire+0x301/0x370
[   92.463288][   T36]  ? rcu_is_watching+0x12/0xc0
[   92.463368][   T36]  process_one_work+0xa23/0x1940
[   92.463500][   T36]  ? __pfx_process_one_work+0x10/0x10
[   92.463540][   T36]  ? __pfx_cleanup_net+0x10/0x10
[   92.463574][   T36]  worker_thread+0x5ef/0xe50
[   92.463618][   T36]  ? __pfx_worker_thread+0x10/0x10
[   92.463657][   T36]  ? kthread+0x13a/0x450
[   92.463685][   T36]  ? __pfx_worker_thread+0x10/0x10
[   92.463717][   T36]  kthread+0x370/0x450
[   92.463747][   T36]  ? __pfx_kthread+0x10/0x10
[   92.463779][   T36]  ret_from_fork+0x72b/0xd50
[   92.463809][   T36]  ? __pfx_ret_from_fork+0x10/0x10
[   92.463840][   T36]  ? __switch_to+0x800/0x10f0
[   92.463880][   T36]  ? __switch_to_asm+0x39/0x70
[   92.463915][   T36]  ? __pfx_kthread+0x10/0x10
[   92.463946][   T36]  ret_from_fork_asm+0x1a/0x30
[   92.463991][   T36]  </TASK>
[   92.464012][   T36] ==================================================================
[   92.772868][   T36] Kernel panic - not syncing: KASAN: panic_on_warn set ...
[   92.780396][   T36] CPU: 0 UID: 0 PID: 36 Comm: kworker/u8:2 Not tainted syzkaller #0 PREEMPT(full) 
[   92.790031][   T36] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
[   92.800267][   T36] Workqueue: netns cleanup_net
[   92.805109][   T36] Call Trace:
[   92.808440][   T36]  <TASK>
[   92.811417][   T36]  dump_stack_lvl+0x100/0x190
[   92.816229][   T36]  vpanic+0x552/0x970
[   92.820274][   T36]  ? __pfx_vpanic+0x10/0x10
[   92.824842][   T36]  ? rcu_is_watching+0x12/0xc0
[   92.829669][   T36]  ? trace_irq_enable.constprop.0+0x122/0x160
[   92.835913][   T36]  ? down_write_nested+0xb4/0x200
[   92.841014][   T36]  panic+0xd1/0xe0
[   92.844800][   T36]  ? __pfx_panic+0x10/0x10
[   92.849264][   T36]  ? check_panic_on_warn+0x1f/0x90
[   92.854429][   T36]  check_panic_on_warn.cold+0x19/0x34
[   92.859848][   T36]  end_report.part.0+0x3a/0x90
[   92.864760][   T36]  kasan_report.cold+0xe/0x18
[   92.869508][   T36]  ? down_write_nested+0xb4/0x200
[   92.874628][   T36]  kasan_check_range+0x10f/0x1e0
[   92.879623][   T36]  down_write_nested+0xb4/0x200
[   92.884625][   T36]  ? __simple_recursive_removal+0x7f/0x5c0
[   92.890505][   T36]  ? __pfx_down_write_nested+0x10/0x10
[   92.896033][   T36]  ? lock_release+0x24d/0x310
[   92.900788][   T36]  ? do_raw_spin_unlock+0x145/0x1e0
[   92.906176][   T36]  __simple_recursive_removal+0x7f/0x5c0
[   92.911965][   T36]  ? __pfx_remove_one+0x10/0x10
[   92.916896][   T36]  ? mntput+0x70/0xa0
[   92.920939][   T36]  debugfs_remove+0x5d/0x80
[   92.925495][   T36]  nsim_destroy+0x6a/0x970
[   92.929962][   T36]  ? mntput_no_expire+0x202/0x220
[   92.935044][   T36]  __nsim_dev_port_del+0x1c2/0x2b0
[   92.940226][   T36]  nsim_dev_reload_destroy+0x10a/0x4a0
[   92.945728][   T36]  ? xa_get_mark+0x19c/0x750
[   92.950360][   T36]  ? lock_release+0x24d/0x310
[   92.955078][   T36]  nsim_dev_reload_down+0x66/0xd0
[   92.960223][   T36]  devlink_reload+0x1ae/0x7a0
[   92.964932][   T36]  ? __pfx_devlink_reload+0x10/0x10
[   92.970170][   T36]  devlink_pernet_pre_exit+0x247/0x370
[   92.975679][   T36]  ? iput.part.0+0x1a0/0x1050
[   92.980407][   T36]  ? __pfx_devlink_pernet_pre_exit+0x10/0x10
[   92.986708][   T36]  ? iput+0x3a/0x40
[   92.990650][   T36]  ? sock_release+0x14d/0x1c0
[   92.995410][   T36]  ? __pfx_devlink_pernet_pre_exit+0x10/0x10
[   93.001440][   T36]  ops_undo_list+0x187/0xab0
[   93.006072][   T36]  ? __pfx_ops_undo_list+0x10/0x10
[   93.011244][   T36]  ? rcu_is_watching+0x12/0xc0
[   93.016081][   T36]  ? cleanup_net+0x332/0x920
[   93.020714][   T36]  ? lock_release+0x24d/0x310
[   93.025452][   T36]  ? idr_destroy+0x62/0x2e0
[   93.030007][   T36]  cleanup_net+0x499/0x920
[   93.034648][   T36]  ? __pfx_cleanup_net+0x10/0x10
[   93.039645][   T36]  ? rcu_is_watching+0x12/0xc0
[   93.044549][   T36]  ? lock_acquire+0x301/0x370
[   93.049372][   T36]  ? rcu_is_watching+0x12/0xc0
[   93.054634][   T36]  process_one_work+0xa23/0x1940
[   93.059802][   T36]  ? __pfx_process_one_work+0x10/0x10
[   93.065227][   T36]  ? __pfx_cleanup_net+0x10/0x10
[   93.070244][   T36]  worker_thread+0x5ef/0xe50
[   93.074965][   T36]  ? __pfx_worker_thread+0x10/0x10
[   93.080203][   T36]  ? kthread+0x13a/0x450
[   93.084484][   T36]  ? __pfx_worker_thread+0x10/0x10
[   93.089720][   T36]  kthread+0x370/0x450
[   93.093825][   T36]  ? __pfx_kthread+0x10/0x10
[   93.098662][   T36]  ret_from_fork+0x72b/0xd50
[   93.103320][   T36]  ? __pfx_ret_from_fork+0x10/0x10
[   93.108847][   T36]  ? __switch_to+0x800/0x10f0
[   93.113675][   T36]  ? __switch_to_asm+0x39/0x70
[   93.118505][   T36]  ? __pfx_kthread+0x10/0x10
[   93.123162][   T36]  ret_from_fork_asm+0x1a/0x30
[   93.127988][   T36]  </TASK>
[   93.131657][   T36] Kernel Offset: disabled
[   93.136033][   T36] Rebooting in 86400 seconds..


syzkaller build log:
go env (err=<nil>)
AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE='auto'
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/syzkaller/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/syzkaller/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build3995708942=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/syzkaller/jobs/linux/gopath/src/github.com/google/syzkaller/go.mod'
GOMODCACHE='/syzkaller/jobs/linux/gopath/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/syzkaller/jobs/linux/gopath'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/syzkaller/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.26.0'
GOWORK=''
PKG_CONFIG='pkg-config'

git status (err=<nil>)
HEAD detached at 4f06757f6
nothing to commit, working tree clean


tput: No value for $TERM and no -T specified
tput: No value for $TERM and no -T specified
Makefile:31: run command via tools/syz-env for best compatibility, see:
Makefile:32: https://github.com/google/syzkaller/blob/master/docs/contributing.md#using-syz-env
go list -f '{{.Stale}}' -ldflags="-s -w -X github.com/google/syzkaller/prog.GitRevision=4f06757f683a802254a4c8edbfe67ff801904c5e -X github.com/google/syzkaller/prog.gitRevisionDate=20260612-145234"  ./sys/syz-sysgen | grep -q false || go install -ldflags="-s -w -X github.com/google/syzkaller/prog.GitRevision=4f06757f683a802254a4c8edbfe67ff801904c5e -X github.com/google/syzkaller/prog.gitRevisionDate=20260612-145234"  ./sys/syz-sysgen
make .descriptions
tput: No value for $TERM and no -T specified
tput: No value for $TERM and no -T specified
Makefile:31: run command via tools/syz-env for best compatibility, see:
Makefile:32: https://github.com/google/syzkaller/blob/master/docs/contributing.md#using-syz-env
bin/syz-sysgen
touch .descriptions
GOOS=linux GOARCH=amd64 go build -ldflags="-s -w -X github.com/google/syzkaller/prog.GitRevision=4f06757f683a802254a4c8edbfe67ff801904c5e -X github.com/google/syzkaller/prog.gitRevisionDate=20260612-145234"  -o ./bin/linux_amd64/syz-execprog github.com/google/syzkaller/tools/syz-execprog
mkdir -p ./bin/linux_amd64
g++ -o ./bin/linux_amd64/syz-executor executor/executor.cc \
	-m64 -O2 -pthread -Wall -Werror -Wparentheses -Wunused-const-variable -Wframe-larger-than=16384 -Wno-stringop-overflow -Wno-array-bounds -Wno-format-overflow -Wno-unused-but-set-variable -Wno-unused-command-line-argument -static-pie -std=c++17 -I. -Iexecutor/_include   -DGOOS_linux=1 -DGOARCH_amd64=1 \
	-DHOSTGOOS_linux=1 -DGIT_REVISION=\"4f06757f683a802254a4c8edbfe67ff801904c5e\"
/usr/bin/ld: /tmp/ccxfdxNm.o: in function `Connection::Connect(char const*, char const*)':
executor.cc:(.text._ZN10Connection7ConnectEPKcS1_[_ZN10Connection7ConnectEPKcS1_]+0x386): warning: Using 'gethostbyname' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
./tools/check-syzos.sh 2>/dev/null


Error text is too large and was truncated, full error text is at:
https://syzkaller.appspot.com/x/error.txt?x=160368ea580000


Tested on:

commit:         e771677c Merge tag 'for-linus-iommufd' of git://git.ke..
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
kernel config:  https://syzkaller.appspot.com/x/.config?x=ea349aa18d06ec5e
dashboard link: https://syzkaller.appspot.com/bug?extid=6c25f4750230faf70be9
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
patch:          https://syzkaller.appspot.com/x/patch.diff?x=177a74fe580000