Date:   Sat, 21 Apr 2018 12:37:01 -0700
From:   Eric Biggers <ebiggers3@...il.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com,
        rostedt@...dmis.org, syzkaller-bugs@...glegroups.com,
        netdev@...r.kernel.org,
        syzbot 
        <bot+a9dbb3c3e64b62536a4bc5ee7bbd4ca627566188@...kaller.appspotmail.com>
Subject: Re: WARNING in perf_trace_buf_alloc (2)

[+bpf maintainers and netdev]

On Mon, Nov 06, 2017 at 03:56:01AM -0800, syzbot wrote:
> 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..
> 
> 
> ---
> This bug is generated by a dumb bot. It may contain errors.
> See https://goo.gl/tpsmEJ for details.
> Direct all questions to syzkaller@...glegroups.com.
> Please credit me with: Reported-by: syzbot <syzkaller@...glegroups.com>
> 
> syzbot will keep track of this bug report.
> Once a fix for this bug is committed, please reply to this email with:
> #syz fix: exact-commit-title
> To mark this as a duplicate of another syzbot report, please reply with:
> #syz dup: exact-subject-of-another-report
> If it's a one-off invalid bug report, please reply with:
> #syz invalid
> Note: if the crash happens again, it will cause creation of a new bug
> report.
> Note: all commands must start from beginning of the line.

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);
        }
}

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