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

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

[syzbot]

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

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

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+6c25f4750230faf70be9@syzkaller.appspotmail.com
Tested-by: syzbot+6c25f4750230faf70be9@syzkaller.appspotmail.com

Tested on:

commit:         6c00e85c Merge branch 'net-sched-finish-the-qdisc_dequ..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git main
console output: https://syzkaller.appspot.com/x/log.txt?x=13cff1fe580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=eb3cf873145f98c4
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=13ec661c580000

Note: testing is done by a robot and is best-effort only.

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

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+6c25f4750230faf70be9@syzkaller.appspotmail.com
Tested-by: syzbot+6c25f4750230faf70be9@syzkaller.appspotmail.com

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
console output: https://syzkaller.appspot.com/x/log.txt?x=14ce93b6580000
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=110e93b6580000

Note: testing is done by a robot and is best-effort only.

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

[syzbot]

Hello,

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

failed to copy syz-execprog to VM: scp failed: timedout after 1m0s ["scp" "-P" "22" "-F" "/dev/null" "-o" "UserKnownHostsFile=/dev/null" "-o" "IdentitiesOnly=yes" "-o" "BatchMode=yes" "-o" "StrictHostKeyChecking=no" "-o" "ConnectTimeout=10" "-v" "-O" "/syzkaller/jobs/linux/gopath/src/github.com/google/syzkaller/bin/linux_amd64/syz-execprog" "root@10.128.1.113:ci-qemu-gce-upstream-auto-test-job/syz-execprog"]



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-build368877244=/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/ccyi0Yf5.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



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=17b693b6580000

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

[syzbot]

Hello,

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

failed to apply patch:
error: corrupt patch at line 6



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=4e4d2284f2ffa41
dashboard link: https://syzkaller.appspot.com/bug?extid=6c25f4750230faf70be9
compiler:       
patch:          https://syzkaller.appspot.com/x/patch.diff?x=102f6d56580000

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

[syzbot]

Hello,

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

failed to apply patch:
error: corrupt patch at line 6



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=4e4d2284f2ffa41
dashboard link: https://syzkaller.appspot.com/bug?extid=6c25f4750230faf70be9
compiler:       
patch:          https://syzkaller.appspot.com/x/patch.diff?x=125c9986580000

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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    062871f1371b Merge tag 'pinctrl-v7.1-3' of git://git.kerne..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=148da8ae580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4e4d2284f2ffa41
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
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=123143b6580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d66ac4b1a707/disk-062871f1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5fb941439264/vmlinux-062871f1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ed65e46ebbc3/bzImage-062871f1.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6c25f4750230faf70be9@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in debugfs_u32_get+0x65/0x80 fs/debugfs/file.c:657
Read of size 4 at addr ffff88807c8e5b00 by task syz.2.10230/16881

CPU: 0 UID: 0 PID: 16881 Comm: syz.2.10230 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0x13d/0x4b0 mm/kasan/report.c:482
 kasan_report+0xdf/0x1d0 mm/kasan/report.c:595
 debugfs_u32_get+0x65/0x80 fs/debugfs/file.c:657
 simple_attr_read+0x16b/0x350 fs/libfs.c:1368
 debugfs_attr_read+0x74/0xb0 fs/debugfs/file.c:523
 vfs_read+0x1e4/0xb30 fs/read_write.c:572
 ksys_read+0x12a/0x250 fs/read_write.c:717
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x840 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa7fd79ce59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe85aad168 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007fa7fda15fa0 RCX: 00007fa7fd79ce59
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007fa7fd832d6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa7fda15fac R14: 00007fa7fda15fa0 R15: 00007fa7fda15fa0
 </TASK>

Allocated by task 14078:
 kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
 kasan_save_track+0x14/0x30 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __do_kmalloc_node mm/slub.c:5296 [inline]
 __kvmalloc_node_noprof+0x360/0xa00 mm/slub.c:6833
 alloc_netdev_mqs+0xd7/0x1560 net/core/dev.c:12029
 nsim_create+0x94/0x1420 drivers/net/netdevsim/netdev.c:1133
 __nsim_dev_port_add+0x3ba/0x8f0 drivers/net/netdevsim/dev.c:1509
 nsim_dev_port_add_all drivers/net/netdevsim/dev.c:1570 [inline]
 nsim_drv_probe+0xeb7/0x14b0 drivers/net/netdevsim/dev.c:1731
 call_driver_probe drivers/base/dd.c:631 [inline]
 really_probe+0x241/0xa60 drivers/base/dd.c:709
 __driver_probe_device+0x22e/0x480 drivers/base/dd.c:871
 driver_probe_device+0x4c/0x1b0 drivers/base/dd.c:901
 __device_attach_driver+0x1df/0x340 drivers/base/dd.c:1029
 bus_for_each_drv+0x159/0x1e0 drivers/base/bus.c:500
 __device_attach+0x1e4/0x4d0 drivers/base/dd.c:1101
 device_initial_probe+0xaf/0xd0 drivers/base/dd.c:1156
 bus_probe_device+0x64/0x160 drivers/base/bus.c:613
 device_add+0x1210/0x1950 drivers/base/core.c:3706
 nsim_bus_dev_new drivers/net/netdevsim/bus.c:471 [inline]
 new_device_store+0x40b/0x700 drivers/net/netdevsim/bus.c:191
 bus_attr_store+0x74/0xb0 drivers/base/bus.c:172
 sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:142
 kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:352
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x6ac/0x1070 fs/read_write.c:688
 ksys_write+0x12a/0x250 fs/read_write.c:740
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x840 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 13:
 kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
 kasan_save_track+0x14/0x30 mm/kasan/common.c:78
 kasan_save_free_info+0x3b/0x70 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5f/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2689 [inline]
 slab_free mm/slub.c:6251 [inline]
 kfree+0x223/0x6c0 mm/slub.c:6566
 device_release+0xd2/0x270 drivers/base/core.c:2566
 kobject_cleanup lib/kobject.c:689 [inline]
 kobject_release lib/kobject.c:720 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x1f7/0x640 lib/kobject.c:737
 put_device+0x1f/0x30 drivers/base/core.c:3814
 free_netdev+0x5ef/0x8c0 net/core/dev.c:12223
 __nsim_dev_port_del+0x194/0x2b0 drivers/net/netdevsim/dev.c:1547
 nsim_dev_port_del_all drivers/net/netdevsim/dev.c:1561 [inline]
 nsim_dev_reload_destroy+0x10a/0x4a0 drivers/net/netdevsim/dev.c:1785
 nsim_dev_reload_down+0x66/0xd0 drivers/net/netdevsim/dev.c:1038
 devlink_reload+0x1ae/0x7a0 net/devlink/dev.c:462
 devlink_pernet_pre_exit+0x247/0x370 net/devlink/core.c:560
 ops_pre_exit_list net/core/net_namespace.c:161 [inline]
 ops_undo_list+0x187/0xab0 net/core/net_namespace.c:234
 cleanup_net+0x499/0x920 net/core/net_namespace.c:702
 process_one_work+0xa0e/0x1980 kernel/workqueue.c:3314
 process_scheduled_works kernel/workqueue.c:3397 [inline]
 worker_thread+0x5ef/0xe50 kernel/workqueue.c:3478
 kthread+0x370/0x450 kernel/kthread.c:436
 ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

The buggy address belongs to the object at ffff88807c8e4000
 which belongs to the cache kmalloc-cg-8k of size 8192
The buggy address is located 6912 bytes inside of
 freed 8192-byte region [ffff88807c8e4000, ffff88807c8e6000)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7c8e0
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
memcg:ffff88807c8e2011
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88813fe47640 dead000000000100 dead000000000122
raw: 0000000000000000 0000400000020002 00000000f5000000 ffff88807c8e2011
head: 00fff00000000040 ffff88813fe47640 dead000000000100 dead000000000122
head: 0000000000000000 0000400000020002 00000000f5000000 ffff88807c8e2011
head: 00fff00000000003 fffffffffffffe01 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd60c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_RETRY_MAYFAIL|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5738, tgid 5738 (syz-executor), ts 350789534111, free_ts 350786879056
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0xfd/0x120 mm/page_alloc.c:1853
 prep_new_page mm/page_alloc.c:1861 [inline]
 get_page_from_freelist+0x11a6/0x3410 mm/page_alloc.c:3941
 __alloc_frozen_pages_noprof+0x27c/0x2bc0 mm/page_alloc.c:5221
 alloc_slab_page mm/slub.c:3278 [inline]
 allocate_slab mm/slub.c:3467 [inline]
 new_slab+0xa6/0x6c0 mm/slub.c:3525
 refill_objects+0x277/0x420 mm/slub.c:7272
 refill_sheaf mm/slub.c:2816 [inline]
 __pcs_replace_empty_main+0x375/0x650 mm/slub.c:4652
 alloc_from_pcs mm/slub.c:4750 [inline]
 slab_alloc_node mm/slub.c:4884 [inline]
 __do_kmalloc_node mm/slub.c:5295 [inline]
 __kvmalloc_node_noprof+0x7da/0xa00 mm/slub.c:6833
 alloc_netdev_mqs+0xd7/0x1560 net/core/dev.c:12029
 rtnl_create_link+0xc13/0xf80 net/core/rtnetlink.c:3672
 rtnl_newlink_create net/core/rtnetlink.c:3854 [inline]
 __rtnl_newlink net/core/rtnetlink.c:3995 [inline]
 rtnl_newlink+0x13bd/0x2380 net/core/rtnetlink.c:4110
 rtnetlink_rcv_msg+0x95e/0xe90 net/core/rtnetlink.c:6997
 netlink_rcv_skb+0x159/0x420 net/netlink/af_netlink.c:2555
 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
 netlink_unicast+0x585/0x850 net/netlink/af_netlink.c:1344
 netlink_sendmsg+0x8b0/0xda0 net/netlink/af_netlink.c:1899
 sock_sendmsg_nosec net/socket.c:787 [inline]
 __sock_sendmsg net/socket.c:802 [inline]
 __sys_sendto+0x468/0x4b0 net/socket.c:2266
 __do_sys_sendto net/socket.c:2273 [inline]
 __se_sys_sendto net/socket.c:2269 [inline]
 __x64_sys_sendto+0xe0/0x1c0 net/socket.c:2269
page last free pid 5762 tgid 5762 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1397 [inline]
 __free_frozen_pages+0x794/0x10a0 mm/page_alloc.c:2938
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x47/0xf0 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x1a0/0x1f0 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x69/0x90 mm/kasan/common.c:350
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4570 [inline]
 slab_alloc_node mm/slub.c:4899 [inline]
 __kmalloc_cache_noprof+0x243/0x6f0 mm/slub.c:5415
 kmalloc_noprof include/linux/slab.h:950 [inline]
 kzalloc_noprof include/linux/slab.h:1188 [inline]
 ref_tracker_alloc+0x190/0x590 lib/ref_tracker.c:270
 __netdev_tracker_alloc include/linux/netdevice.h:4471 [inline]
 netdev_hold include/linux/netdevice.h:4500 [inline]
 netdev_hold include/linux/netdevice.h:4495 [inline]
 netdev_queue_add_kobject net/core/net-sysfs.c:1979 [inline]
 netdev_queue_update_kobjects+0x2db/0x6f0 net/core/net-sysfs.c:2041
 register_queue_kobjects net/core/net-sysfs.c:2104 [inline]
 netdev_register_kobject+0x2b3/0x3d0 net/core/net-sysfs.c:2347
 register_netdevice+0x151c/0x24b0 net/core/dev.c:11423
 __ip_tunnel_create+0x52b/0x670 net/ipv4/ip_tunnel.c:268
 ip_tunnel_init_net+0x230/0x780 net/ipv4/ip_tunnel.c:1147
 ops_init+0x1e2/0x5f0 net/core/net_namespace.c:137
 setup_net+0x118/0x3a0 net/core/net_namespace.c:446
 copy_net_ns+0x46f/0x7c0 net/core/net_namespace.c:579
 create_new_namespaces+0x3ea/0xac0 kernel/nsproxy.c:132
 unshare_nsproxy_namespaces+0xf2/0x220 kernel/nsproxy.c:234

Memory state around the buggy address:
 ffff88807c8e5a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88807c8e5a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88807c8e5b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff88807c8e5b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88807c8e5c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

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.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup