[syzbot] [net?] WARNING: suspicious RCU usage in task_cls_state

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 079e5c56a5c4 bpf: Fix error return value in bpf_copy_from_..
git tree: bpf-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=178ae170580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c6c517d2f439239
dashboard link: https://syzkaller.appspot.com/bug?extid=b4169a1cfb945d2ed0ec
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13bc35f4580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15f195f4580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/8d7d35d067bc/disk-079e5c56.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/74d2648ea7f4/vmlinux-079e5c56.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e751e253ee4f/bzImage-079e5c56.xz

The issue was bisected to:

commit ee971630f20fd421fffcdc4543731ebcb54ed6d0
Author: Feng Yang <yang...@kylinos.cn>
Date: Tue May 6 06:14:33 2025 +0000

bpf: Allow some trace helpers for all prog types

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=14cd68e8580000
final oops: https://syzkaller.appspot.com/x/report.txt?x=16cd68e8580000
console output: https://syzkaller.appspot.com/x/log.txt?x=12cd68e8580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b4169a...@syzkaller.appspotmail.com
Fixes: ee971630f20f ("bpf: Allow some trace helpers for all prog types")

=============================
WARNING: suspicious RCU usage
6.15.0-rc4-syzkaller-g079e5c56a5c4 #0 Not tainted
-----------------------------
net/core/netclassid_cgroup.c:24 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
1 lock held by syz-executor296/5833:
#0: ffffffff8df3ba40 (rcu_read_lock_trace){....}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
#0: ffffffff8df3ba40 (rcu_read_lock_trace){....}-{0:0}, at: rcu_read_lock_trace+0x38/0x80 include/linux/rcupdate_trace.h:58

stack backtrace:
CPU: 0 UID: 0 PID: 5833 Comm: syz-executor296 Not tainted 6.15.0-rc4-syzkaller-g079e5c56a5c4 #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
lockdep_rcu_suspicious+0x140/0x1d0 kernel/locking/lockdep.c:6865
task_cls_state+0x1a5/0x1d0 net/core/netclassid_cgroup.c:23
__task_get_classid include/net/cls_cgroup.h:50 [inline]
____bpf_get_cgroup_classid_curr net/core/filter.c:3086 [inline]
bpf_get_cgroup_classid_curr+0x18/0x60 net/core/filter.c:3084
bpf_prog_83da9cb0e78d4768+0x2c/0x5a
bpf_dispatcher_nop_func include/linux/bpf.h:1322 [inline]
__bpf_prog_run include/linux/filter.h:718 [inline]
bpf_prog_run include/linux/filter.h:725 [inline]
bpf_prog_run_pin_on_cpu+0x67/0x150 include/linux/filter.h:742
bpf_prog_test_run_syscall+0x312/0x4b0 net/bpf/test_run.c:1564
bpf_prog_test_run+0x2a9/0x340 kernel/bpf/syscall.c:4429
__sys_bpf+0x4a4/0x860 kernel/bpf/syscall.c:5854
__do_sys_bpf kernel/bpf/syscall.c:5943 [inline]
__se_sys_bpf kernel/bpf/syscall.c:5941 [inline]
__x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5941
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fda75b18a69
Code: d8 5b 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffdd0546d48 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fda75b18a69
RDX: 0000000000000048 RSI: 0000200000000500 RDI: 000000000000000a


---
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[Charalampos Mitrodimas]

#syz test: https://github.com/charmitro/linux.git e5c42d49bfb967c3c35f536971f397492d2f46bf

[syzbot]

Hello,

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

Reported-by: syzbot+b4169a...@syzkaller.appspotmail.com
Tested-by: syzbot+b4169a...@syzkaller.appspotmail.com

Tested on:

commit: e5c42d49 net: Fix RCU warning in task_cls_state for BP..
git tree: https://github.com/charmitro/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=12750a0c580000

kernel config: https://syzkaller.appspot.com/x/.config?x=c6c517d2f439239
dashboard link: https://syzkaller.appspot.com/bug?extid=b4169a1cfb945d2ed0ec
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6

Note: no patches were applied.
Note: testing is done by a robot and is best-effort only.