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Message-ID: <YxXZT6NxSSLufivZ@krava>
Date:   Mon, 5 Sep 2022 13:11:11 +0200
From:   Jiri Olsa <olsajiri@...il.com>
To:     syzbot <syzbot+2251879aa068ad9c960d@...kaller.appspotmail.com>
Cc:     andrii@...nel.org, ast@...nel.org, bpf@...r.kernel.org,
        daniel@...earbox.net, haoluo@...gle.com, john.fastabend@...il.com,
        kpsingh@...nel.org, linux-kernel@...r.kernel.org,
        martin.lau@...ux.dev, sdf@...gle.com, song@...nel.org,
        syzkaller-bugs@...glegroups.com, yhs@...com
Subject: Re: [syzbot] WARNING in bpf_bprintf_prepare (2)

On Sun, Sep 04, 2022 at 02:21:23PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    7fd22855300e Add linux-next specific files for 20220831
> git tree:       linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=14e5668b080000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=3e56c1a274c93753
> dashboard link: https://syzkaller.appspot.com/bug?extid=2251879aa068ad9c960d
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17dc728b080000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=164748d7080000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+2251879aa068ad9c960d@...kaller.appspotmail.com
> 
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 3601 at kernel/bpf/helpers.c:769 try_get_fmt_tmp_buf kernel/bpf/helpers.c:769 [inline]
> WARNING: CPU: 1 PID: 3601 at kernel/bpf/helpers.c:769 bpf_bprintf_prepare+0xf31/0x11a0 kernel/bpf/helpers.c:817
> Modules linked in:
> CPU: 1 PID: 3601 Comm: strace-static-x Not tainted 6.0.0-rc3-next-20220831-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022
> RIP: 0010:try_get_fmt_tmp_buf kernel/bpf/helpers.c:769 [inline]
> RIP: 0010:bpf_bprintf_prepare+0xf31/0x11a0 kernel/bpf/helpers.c:817
> Code: ff e8 93 9f ea ff 48 83 7c 24 08 00 41 bd 04 00 00 00 0f 85 8a fa ff ff e8 7c 9f ea ff 8d 6b 03 e9 f7 f6 ff ff e8 6f 9f ea ff <0f> 0b 65 ff 0d 8e ba 71 7e bf 01 00 00 00 41 bc f0 ff ff ff e8 16
> RSP: 0018:ffffc90003cfeb70 EFLAGS: 00010093
> RAX: 0000000000000000 RBX: 0000000000000002 RCX: 0000000000000000
> RDX: ffff8880219b3a80 RSI: ffffffff819186b1 RDI: 0000000000000005
> RBP: ffffc90003cfeca0 R08: 0000000000000005 R09: 0000000000000003
> R10: 0000000000000004 R11: 0000000000000001 R12: 0000000000000003
> R13: 0000000000000004 R14: ffffc90003cfed58 R15: 0000000000000003
> FS:  0000000001655340(0000) GS:ffff8880b9b00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020003000 CR3: 0000000074d58000 CR4: 00000000003506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  ____bpf_trace_printk kernel/trace/bpf_trace.c:383 [inline]
>  bpf_trace_printk+0xab/0x170 kernel/trace/bpf_trace.c:374
>  bpf_prog_0605f9f479290f07+0x2f/0x33
>  bpf_dispatcher_nop_func include/linux/bpf.h:904 [inline]
>  __bpf_prog_run include/linux/filter.h:594 [inline]
>  bpf_prog_run include/linux/filter.h:601 [inline]
>  __bpf_trace_run kernel/trace/bpf_trace.c:2046 [inline]
>  bpf_trace_run2+0x110/0x340 kernel/trace/bpf_trace.c:2083
>  __bpf_trace_contention_begin+0xb5/0xf0 include/trace/events/lock.h:95
>  trace_contention_begin.constprop.0+0xda/0x1b0 include/trace/events/lock.h:95
>  __pv_queued_spin_lock_slowpath+0x103/0xb50 kernel/locking/qspinlock.c:405
>  pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:591 [inline]
>  queued_spin_lock_slowpath arch/x86/include/asm/qspinlock.h:51 [inline]
>  queued_spin_lock include/asm-generic/qspinlock.h:114 [inline]
>  do_raw_spin_lock+0x200/0x2a0 kernel/locking/spinlock_debug.c:115
>  __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:111 [inline]
>  _raw_spin_lock_irqsave+0x41/0x50 kernel/locking/spinlock.c:162
>  ____bpf_trace_printk kernel/trace/bpf_trace.c:388 [inline]
>  bpf_trace_printk+0xcf/0x170 kernel/trace/bpf_trace.c:374
>  bpf_prog_0605f9f479290f07+0x2f/0x33
>  bpf_dispatcher_nop_func include/linux/bpf.h:904 [inline]
>  __bpf_prog_run include/linux/filter.h:594 [inline]
>  bpf_prog_run include/linux/filter.h:601 [inline]
>  __bpf_trace_run kernel/trace/bpf_trace.c:2046 [inline]
>  bpf_trace_run2+0x110/0x340 kernel/trace/bpf_trace.c:2083
>  __bpf_trace_contention_begin+0xb5/0xf0 include/trace/events/lock.h:95
>  trace_contention_begin.constprop.0+0xda/0x1b0 include/trace/events/lock.h:95
>  __pv_queued_spin_lock_slowpath+0x103/0xb50 kernel/locking/qspinlock.c:405
>  pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:591 [inline]
>  queued_spin_lock_slowpath arch/x86/include/asm/qspinlock.h:51 [inline]
>  queued_spin_lock include/asm-generic/qspinlock.h:114 [inline]
>  do_raw_spin_lock+0x200/0x2a0 kernel/locking/spinlock_debug.c:115
>  __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:111 [inline]
>  _raw_spin_lock_irqsave+0x41/0x50 kernel/locking/spinlock.c:162
>  ____bpf_trace_printk kernel/trace/bpf_trace.c:388 [inline]
>  bpf_trace_printk+0xcf/0x170 kernel/trace/bpf_trace.c:374
>  bpf_prog_0605f9f479290f07+0x2f/0x33
>  bpf_dispatcher_nop_func include/linux/bpf.h:904 [inline]
>  __bpf_prog_run include/linux/filter.h:594 [inline]
>  bpf_prog_run include/linux/filter.h:601 [inline]
>  __bpf_trace_run kernel/trace/bpf_trace.c:2046 [inline]
>  bpf_trace_run2+0x110/0x340 kernel/trace/bpf_trace.c:2083
>  __bpf_trace_contention_begin+0xb5/0xf0 include/trace/events/lock.h:95
>  trace_contention_begin.constprop.0+0xda/0x1b0 include/trace/events/lock.h:95
>  __pv_queued_spin_lock_slowpath+0x103/0xb50 kernel/locking/qspinlock.c:405
>  pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:591 [inline]
>  queued_spin_lock_slowpath arch/x86/include/asm/qspinlock.h:51 [inline]
>  queued_spin_lock include/asm-generic/qspinlock.h:114 [inline]
>  do_raw_spin_lock+0x200/0x2a0 kernel/locking/spinlock_debug.c:115
>  __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:111 [inline]
>  _raw_spin_lock_irqsave+0x41/0x50 kernel/locking/spinlock.c:162
>  ____bpf_trace_printk kernel/trace/bpf_trace.c:388 [inline]
>  bpf_trace_printk+0xcf/0x170 kernel/trace/bpf_trace.c:374
>  bpf_prog_0605f9f479290f07+0x2f/0x33
>  bpf_dispatcher_nop_func include/linux/bpf.h:904 [inline]
>  __bpf_prog_run include/linux/filter.h:594 [inline]
>  bpf_prog_run include/linux/filter.h:601 [inline]
>  __bpf_trace_run kernel/trace/bpf_trace.c:2046 [inline]
>  bpf_trace_run2+0x110/0x340 kernel/trace/bpf_trace.c:2083
>  __bpf_trace_contention_begin+0xb5/0xf0 include/trace/events/lock.h:95
>  trace_contention_begin+0xc0/0x150 include/trace/events/lock.h:95
>  __mutex_lock_common kernel/locking/mutex.c:605 [inline]
>  __mutex_lock+0x13c/0x1350 kernel/locking/mutex.c:747
>  __pipe_lock fs/pipe.c:103 [inline]
>  pipe_write+0x132/0x1be0 fs/pipe.c:431
>  call_write_iter include/linux/fs.h:2188 [inline]
>  new_sync_write fs/read_write.c:491 [inline]
>  vfs_write+0x9e9/0xdd0 fs/read_write.c:578
>  ksys_write+0x1e8/0x250 fs/read_write.c:631
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd

looks like __bpf_trace_contention_begin needs bpf_prog_active check
(like below untested), which would prevent the recursion and bail
out after 2nd invocation

should be easy to reproduce, will check

jirka


---
diff --git a/include/trace/bpf_probe.h b/include/trace/bpf_probe.h
index 6a13220d2d27..481b057cc8d9 100644
--- a/include/trace/bpf_probe.h
+++ b/include/trace/bpf_probe.h
@@ -4,6 +4,8 @@
 
 #ifdef CONFIG_BPF_EVENTS
 
+DECLARE_PER_CPU(int, bpf_prog_active);
+
 #undef __entry
 #define __entry entry
 
@@ -82,7 +84,11 @@ static notrace void							\
 __bpf_trace_##call(void *__data, proto)					\
 {									\
 	struct bpf_prog *prog = __data;					\
+	if (unlikely(__this_cpu_inc_return(bpf_prog_active) != 1))	\
+		goto out;						\
 	CONCATENATE(bpf_trace_run, COUNT_ARGS(args))(prog, CAST_TO_U64(args));	\
+out:									\
+        __this_cpu_dec(bpf_prog_active);				\
 }
 
 #undef DECLARE_EVENT_CLASS

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