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

[Yonghong Song <yhs@fb.com>]

On 11/12/20 9:37 PM, Matt Mullins wrote:
> 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/trace/bpf_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

Maybe you can still post the patch, so people can review and make 
suggestions which may lead to a *better* solution.

> 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
>>> ==================================================================
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