[syzbot] WARNING in bpf_bprintf_prepare (2)

[syzbot]

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+225187...@syzkaller.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
RIP: 0033:0x4e5c73
Code: c7 c0 b8 ff ff ff 64 c7 00 16 00 00 00 b8 ff ff ff ff c3 0f 1f 40 00 64 8b 04 25 18 00 00 00 85 c0 75 14 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 55 c3 0f 1f 40 00 48 83 ec 28 48 89 54 24 18
RSP: 002b:00007ffc4f3ec0a8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000019 RCX: 00000000004e5c73
RDX: 0000000000000019 RSI: 0000000001658000 RDI: 0000000000000002
RBP: 0000000001658000 R08: 0000000000000000 R09: 0000000000000003
R10: 00007ffc4f3ec087 R11: 0000000000000246 R12: 0000000000000019
R13: 0000000000617480 R14: 0000000000000019 R15: 0000000000000001
</TASK>


---
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[Jiri Olsa]

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

[Alexei Starovoitov]

I don't think we can use this big hammer here.
raw_tp progs attached to different hooks need to
run on the same cpu otherwise we will lose events.

[Jiri Olsa]

On Tue, Sep 06, 2022 at 08:02:39PM -0700, Alexei Starovoitov wrote:

SNIP

might be good place to use prog->active
I managed to reproduce it localy, will try that

jirka