Netdev List

* Re: WARNING in perf_trace_buf_alloc (2)
From: Alexei Starovoitov @ 2018-04-28  5:23 UTC (permalink / raw)
  To: Eric Biggers
  Cc: Alexei Starovoitov, Daniel Borkmann, linux-kernel, mingo, rostedt,
	syzkaller-bugs, netdev, syzbot
In-Reply-To: <20180421193701.GE1098@sol.localdomain>

On Sat, Apr 21, 2018 at 12:37:01PM -0700, Eric Biggers wrote:
> [+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@googlegroups.com.
> > Please credit me with: Reported-by: syzbot <syzkaller@googlegroups.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

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

> 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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