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

From: syzbot

Date: Thu Jun 18 2026 - 05:29:37 EST

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