WARNING in perf_trace_buf_alloc (2)

[syzbot]

Hello,

syzkaller hit the following crash on
5cb0512c02ecd7e6214e912e4c150f4219ac78e0
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master
compiler: gcc (GCC) 7.1.1 20170620
.config is attached
Raw console output is attached.
C reproducer is attached
syzkaller reproducer is attached. See https://goo.gl/kgGztJ
for information about syzkaller reproducers


------------[ cut here ]------------
WARNING: CPU: 0 PID: 3008 at kernel/trace/trace_event_perf.c:274
perf_trace_buf_alloc+0x12d/0x160 kernel/trace/trace_event_perf.c:273
Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 3008 Comm: syzkaller609027 Not tainted 4.14.0-rc7+ #159
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x194/0x257 lib/dump_stack.c:53
panic+0x1e4/0x417 kernel/panic.c:181
__warn+0x1c4/0x1d9 kernel/panic.c:542
report_bug+0x211/0x2d0 lib/bug.c:184
fixup_bug+0x40/0x90 arch/x86/kernel/traps.c:178
do_trap_no_signal arch/x86/kernel/traps.c:212 [inline]
do_trap+0x260/0x390 arch/x86/kernel/traps.c:261
do_error_trap+0x120/0x390 arch/x86/kernel/traps.c:298
do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:311
invalid_op+0x18/0x20 arch/x86/entry/entry_64.S:906
RIP: 0010:perf_trace_buf_alloc+0x12d/0x160
kernel/trace/trace_event_perf.c:273
RSP: 0018:ffff8801c0fdf760 EFLAGS: 00010286
RAX: 000000000000001c RBX: 1ffff100381fbefe RCX: 0000000000000000
RDX: 000000000000001c RSI: 1ffff100381fbeac RDI: ffffed00381fbee0
RBP: ffff8801c0fdf780 R08: 0000000000000001 R09: 0000000000000000
R10: ffff8801c0fdf7a0 R11: 0000000000000000 R12: 000000000000082c
R13: ffff8801c0fdf810 R14: ffff8801c0fdf890 R15: ffff8801d8b34b40
perf_trace_bpf_map_keyval+0x260/0xbd0 include/trace/events/bpf.h:228
trace_bpf_map_update_elem include/trace/events/bpf.h:274 [inline]
map_update_elem kernel/bpf/syscall.c:597 [inline]
SYSC_bpf kernel/bpf/syscall.c:1478 [inline]
SyS_bpf+0x33eb/0x46a0 kernel/bpf/syscall.c:1453
entry_SYSCALL_64_fastpath+0x1f/0xbe
RIP: 0033:0x445c29
RSP: 002b:00000000007eff68 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007ffe66adb340 RCX: 0000000000445c29
RDX: 0000000000000020 RSI: 000000002053dfe0 RDI: 0000000000000002
RBP: 0000000000000082 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000403280
R13: 0000000000403310 R14: 0000000000000000 R15: 0000000000000000
Dumping ftrace buffer:
(ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
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[Eric Biggers]

[+bpf maintainers and netdev]

This still happens on Linus' tree. It seems one of the BPF tracepoints is
trying to pass a buffer that is too long. Here's a simplified reproducer that
works on Linus' tree (commit 5e7c7806111ade5). Note: it's not 100% reliable for
some reason; you may have to run it a couple times. Daniel or Alexei, can one
of you please look into this more? Thanks!

#include <linux/bpf.h>
#include <linux/perf_event.h>
#include <stdio.h>
#include <sys/syscall.h>
#include <unistd.h>

int main()
{
int tracepoint_id;
FILE *f;

f = fopen("/sys/kernel/debug/tracing/events/bpf/bpf_map_update_elem/id",
"r");
fscanf(f, "%d", &tracepoint_id);

struct perf_event_attr perf_attr = {
.type = PERF_TYPE_TRACEPOINT,
.size = sizeof(perf_attr),
.config = tracepoint_id,
};
syscall(__NR_perf_event_open, &perf_attr, 0, 0, -1, 0);

for (;;) {
union bpf_attr create_attr = {
.map_type = BPF_MAP_TYPE_HASH,
.key_size = 4,
.value_size = 2048,
.max_entries = 1,
};
int fd = syscall(__NR_bpf, BPF_MAP_CREATE,
&create_attr, sizeof(create_attr));

char key[4] = { 0 };
char value[2048] = { 0 };
union bpf_attr update_attr = {
.map_fd = fd,
.key = (unsigned long)key,
.value = (unsigned long)value,
};
syscall(__NR_bpf, BPF_MAP_UPDATE_ELEM,
&update_attr, sizeof(update_attr));
close(fd);
}
}

[Alexei Starovoitov]

right. this is easily reproducible.
looks like tracepoints in bpf core rot quite a bit.
will send a patch to address that soon.

[Eric Biggers]

On Mon, Nov 06, 2017 at 03:56:01AM -0800, syzbot wrote:

This was fixed by commit 4d220ed0f8140c:

#syz fix: bpf: remove tracepoints from bpf core

- Eric