Re: KASAN: vmalloc-out-of-bounds Read in bpf_trace_run3

[Matt Mullins <mmullins@mmlx.us>]

On Wed, Nov 11, 2020 at 03:57:50PM +0100, Dmitry Vyukov wrote:
> On Mon, Nov 2, 2020 at 12:54 PM syzbot
> <syzbot+d29e58bb557324e55e5e@syzkaller.appspotmail.com> wrote:
> >
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    080b6f40 bpf: Don't rely on GCC __attribute__((optimize)) ..
> > git tree:       bpf
> > console output: https://syzkaller.appspot.com/x/log.txt?x=1089d37c500000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=58a4ca757d776bfe
> > dashboard link: https://syzkaller.appspot.com/bug?extid=d29e58bb557324e55e5e
> > compiler:       gcc (GCC) 10.1.0-syz 20200507
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10f4b032500000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1371a47c500000
> >
> > The issue was bisected to:
> >
> > commit 9df1c28bb75217b244257152ab7d788bb2a386d0
> > Author: Matt Mullins <mmullins@fb.com>
> > Date:   Fri Apr 26 18:49:47 2019 +0000
> >
> >     bpf: add writable context for raw tracepoints
> 
> 
> We have a number of kernel memory corruptions related to bpf_trace_run now:
> https://groups.google.com/g/syzkaller-bugs/search?q=kernel%2Ftrace%2Fbpf_trace.c
> 
> Can raw tracepoints "legally" corrupt kernel memory (a-la /dev/kmem)?
> Or they shouldn't?
> 
> Looking at the description of Matt's commit, it seems that corruptions
> should not be possible (bounded buffer, checked size, etc). Then it
> means it's a real kernel bug?

This bug doesn't seem to be related to the writability of the
tracepoint; it bisected to that commit simply because it used
BPF_PROG_TYPE_RAW_TRACEPOINT_WRITABLE for the reproducer and it EINVAL's
before that program type was introduced.  The BPF program it loads is
pretty much a no-op.

The problem here is a kmalloc failure injection into
tracepoint_probe_unregister, but the error is ignored -- so the bpf
program is freed even though the tracepoint is never unregistered.

I have a first pass at a patch to pipe through the error code, but it's
pretty ugly.  It's also called from the file_operations ->release(), for
which errors are solidly ignored in __fput(), so I'm not sure what the
best way to handle ENOMEM is...

> 
> 
> 
> > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=12b6c4da500000
> > final oops:     https://syzkaller.appspot.com/x/report.txt?x=11b6c4da500000
> > console output: https://syzkaller.appspot.com/x/log.txt?x=16b6c4da500000
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+d29e58bb557324e55e5e@syzkaller.appspotmail.com
> > Fixes: 9df1c28bb752 ("bpf: add writable context for raw tracepoints")
> >
> > ==================================================================
> > BUG: KASAN: vmalloc-out-of-bounds in __bpf_trace_run kernel/trace/bpf_trace.c:2045 [inline]
> > BUG: KASAN: vmalloc-out-of-bounds in bpf_trace_run3+0x3e0/0x3f0 kernel/trace/bpf_trace.c:2083
> > Read of size 8 at addr ffffc90000e6c030 by task kworker/0:3/3754
> >
> > CPU: 0 PID: 3754 Comm: kworker/0:3 Not tainted 5.9.0-syzkaller #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> > Workqueue:  0x0 (events)
> > Call Trace:
> >  __dump_stack lib/dump_stack.c:77 [inline]
> >  dump_stack+0x107/0x163 lib/dump_stack.c:118
> >  print_address_description.constprop.0.cold+0x5/0x4c8 mm/kasan/report.c:385
> >  __kasan_report mm/kasan/report.c:545 [inline]
> >  kasan_report.cold+0x1f/0x37 mm/kasan/report.c:562
> >  __bpf_trace_run kernel/trace/bpf_trace.c:2045 [inline]
> >  bpf_trace_run3+0x3e0/0x3f0 kernel/trace/bpf_trace.c:2083
> >  __bpf_trace_sched_switch+0xdc/0x120 include/trace/events/sched.h:138
> >  __traceiter_sched_switch+0x64/0xb0 include/trace/events/sched.h:138
> >  trace_sched_switch include/trace/events/sched.h:138 [inline]
> >  __schedule+0xeb8/0x2130 kernel/sched/core.c:4520
> >  schedule+0xcf/0x270 kernel/sched/core.c:4601
> >  worker_thread+0x14c/0x1120 kernel/workqueue.c:2439
> >  kthread+0x3af/0x4a0 kernel/kthread.c:292
> >  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296
> >
> >
> > Memory state around the buggy address:
> >  ffffc90000e6bf00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
> >  ffffc90000e6bf80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
> > >ffffc90000e6c000: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
> >                                      ^
> >  ffffc90000e6c080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
> >  ffffc90000e6c100: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
> > ==================================================================
> >
> >
> > ---
> > This report is generated by a bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for more information about syzbot.
> > syzbot engineers can be reached at syzkaller@googlegroups.com.
> >
> > syzbot will keep track of this issue. See:
> > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> > For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> > syzbot can test patches for this issue, for details see:
> > https://goo.gl/tpsmEJ#testing-patches
> >
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