Date: Tue, 25 Jun 2024 22:56:46 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Eduard Zingerman
 <eddyz87@...il.com>, Song Liu <song@...nel.org>,
        Yonghong Song <yonghong.song@...ux.dev>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Petr Mladek <pmladek@...e.com>, Steven Rostedt <rostedt@...dmis.org>,
        John Ogness
 <john.ogness@...utronix.de>,
        Sergey Senozhatsky <senozhatsky@...omium.org>
Cc: bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] bpf: defer printk() inside __bpf_prog_run()

syzbot is reporting circular locking dependency inside __bpf_prog_run(),
for fault injection calls printk() despite rq lock is already held.

Guard __bpf_prog_run() using printk_deferred_{enter,exit}() (and
preempt_{disable,enable}() if CONFIG_PREEMPT_RT=n) in order to defer any
printk() messages. (migrate_{disable,enable}() is not needed if
CONFIG_PREEMPT_RT=y because cant_migrate() asserts that caller already
disabled migration.)

======================================================
WARNING: possible circular locking dependency detected
6.10.0-rc4-syzkaller-00874-g84562f9953ec #0 Not tainted
------------------------------------------------------
syz-executor.1/25480 is trying to acquire lock:
ffffffff8e328140 (console_owner){..-.}-{0:0}, at: rcu_try_lock_acquire include/linux/rcupdate.h:334 [inline]
ffffffff8e328140 (console_owner){..-.}-{0:0}, at: srcu_read_lock_nmisafe include/linux/srcu.h:232 [inline]
ffffffff8e328140 (console_owner){..-.}-{0:0}, at: console_srcu_read_lock kernel/printk/printk.c:286 [inline]
ffffffff8e328140 (console_owner){..-.}-{0:0}, at: console_flush_all+0x152/0xfd0 kernel/printk/printk.c:2986

but task is already holding lock:
ffff8880b943e798 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x2a/0x140 kernel/sched/core.c:559

which lock already depends on the new lock.

(...snipped...)

Chain exists of:
  console_owner --> &p->pi_lock --> &rq->__lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&rq->__lock);
                               lock(&p->pi_lock);
                               lock(&rq->__lock);
  lock(console_owner);

 *** DEADLOCK ***

6 locks held by syz-executor.1/25480:
 #0: ffffffff8f5e6f48 (rtnl_mutex){+.+.}-{3:3}, at: dev_ioctl+0x706/0x1340 net/core/dev_ioctl.c:785
 #1: ffffffff8f67dd68 (flowtable_lock){+.+.}-{3:3}, at: nf_flow_table_cleanup+0x23/0xb0 net/netfilter/nf_flow_table_core.c:593
 #2: ffff8880b943e798 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x2a/0x140 kernel/sched/core.c:559
 #3: ffffffff8e333fa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:329 [inline]
 #3: ffffffff8e333fa0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:781 [inline]
 #3: ffffffff8e333fa0 (rcu_read_lock){....}-{1:2}, at: __bpf_trace_run kernel/trace/bpf_trace.c:2402 [inline]
 #3: ffffffff8e333fa0 (rcu_read_lock){....}-{1:2}, at: bpf_trace_run4+0x244/0x590 kernel/trace/bpf_trace.c:2446
 #4: ffffffff8e20fa60 (console_lock){+.+.}-{0:0}, at: _printk+0xd5/0x120 kernel/printk/printk.c:2370
 #5: ffffffff8e20f690 (console_srcu){....}-{0:0}, at: rcu_try_lock_acquire include/linux/rcupdate.h:334 [inline]
 #5: ffffffff8e20f690 (console_srcu){....}-{0:0}, at: srcu_read_lock_nmisafe include/linux/srcu.h:232 [inline]
 #5: ffffffff8e20f690 (console_srcu){....}-{0:0}, at: console_srcu_read_lock kernel/printk/printk.c:286 [inline]
 #5: ffffffff8e20f690 (console_srcu){....}-{0:0}, at: console_flush_all+0x152/0xfd0 kernel/printk/printk.c:2986

stack backtrace:
CPU: 0 PID: 25480 Comm: syz-executor.1 Not tainted 6.10.0-rc4-syzkaller-00874-g84562f9953ec #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
 check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2187
 check_prev_add kernel/locking/lockdep.c:3134 [inline]
 check_prevs_add kernel/locking/lockdep.c:3253 [inline]
 validate_chain+0x18e0/0x5900 kernel/locking/lockdep.c:3869
 __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
 console_lock_spinning_enable kernel/printk/printk.c:1870 [inline]
 console_emit_next_record kernel/printk/printk.c:2922 [inline]
 console_flush_all+0x810/0xfd0 kernel/printk/printk.c:2994
 console_unlock+0x13b/0x4d0 kernel/printk/printk.c:3063
 vprintk_emit+0x5a6/0x770 kernel/printk/printk.c:2345
 _printk+0xd5/0x120 kernel/printk/printk.c:2370
 fail_dump lib/fault-inject.c:45 [inline]
 should_fail_ex+0x391/0x4e0 lib/fault-inject.c:153
 __copy_to_user_inatomic include/linux/uaccess.h:123 [inline]
 copy_to_user_nofault+0x86/0x140 mm/maccess.c:149
 bpf_prog_b0a3dac844962ed2+0x47/0x4d
 bpf_dispatcher_nop_func include/linux/bpf.h:1243 [inline]
 __bpf_prog_run include/linux/filter.h:691 [inline]
 bpf_prog_run include/linux/filter.h:698 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2403 [inline]
 bpf_trace_run4+0x334/0x590 kernel/trace/bpf_trace.c:2446
 __traceiter_sched_switch+0x98/0xd0 include/trace/events/sched.h:222
 trace_sched_switch include/trace/events/sched.h:222 [inline]
 __schedule+0x2587/0x4a20 kernel/sched/core.c:6742
 preempt_schedule_notrace+0x100/0x140 kernel/sched/core.c:7017
 preempt_schedule_notrace_thunk+0x1a/0x30 arch/x86/entry/thunk.S:13
 rcu_is_watching+0x7e/0xb0 kernel/rcu/tree.c:725
 trace_lock_acquire include/trace/events/lock.h:24 [inline]
 lock_acquire+0xe3/0x550 kernel/locking/lockdep.c:5725
 rcu_lock_acquire include/linux/rcupdate.h:329 [inline]
 rcu_read_lock include/linux/rcupdate.h:781 [inline]
 start_flush_work kernel/workqueue.c:4122 [inline]
 __flush_work+0x107/0xd00 kernel/workqueue.c:4181
 flush_work kernel/workqueue.c:4232 [inline]
 flush_delayed_work+0x169/0x1c0 kernel/workqueue.c:4254
 nf_flow_table_gc_cleanup net/netfilter/nf_flow_table_core.c:585 [inline]
 nf_flow_table_cleanup+0x62/0xb0 net/netfilter/nf_flow_table_core.c:595
 flow_offload_netdev_event+0x51/0x70 net/netfilter/nft_flow_offload.c:492
 notifier_call_chain+0x19f/0x3e0 kernel/notifier.c:93
 __dev_notify_flags+0x207/0x400
 dev_change_flags+0xf0/0x1a0 net/core/dev.c:8858
 dev_ifsioc+0x7c8/0xe70 net/core/dev_ioctl.c:529
 dev_ioctl+0x719/0x1340 net/core/dev_ioctl.c:786
 sock_do_ioctl+0x240/0x460 net/socket.c:1236
 sock_ioctl+0x629/0x8e0 net/socket.c:1341
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported-by: syzbot <syzbot+f78380e4eae53c64125c@...kaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=f78380e4eae53c64125c
Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
---
Only compile tested.

 include/linux/filter.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index dd41a93f06b2e..977ae5b486164 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -674,6 +674,10 @@ static __always_inline u32 __bpf_prog_run(const struct bpf_prog *prog,
 	u32 ret;
 
 	cant_migrate();
+#ifndef CONFIG_PREEMPT_RT
+	preempt_disable();
+#endif
+	printk_deferred_enter();
 	if (static_branch_unlikely(&bpf_stats_enabled_key)) {
 		struct bpf_prog_stats *stats;
 		u64 duration, start = sched_clock();
@@ -690,6 +694,10 @@ static __always_inline u32 __bpf_prog_run(const struct bpf_prog *prog,
 	} else {
 		ret = dfunc(ctx, prog->insnsi, prog->bpf_func);
 	}
+	printk_deferred_exit();
+#ifndef CONFIG_PREEMPT_RT
+	preempt_enable();
+#endif
 	return ret;
 }
 
-- 
2.43.0

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