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

[Eric Dumazet]

On 11/13/20 5:08 PM, Yonghong Song wrote:
> 
> 
> 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@xxxxxxxxxxxxxxxxxxxxxxxxx> 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@xxxxxx>
>>>> 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.


ping

This bug is still there.


> 
>> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
>>>> 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
>>>> ==================================================================
> [...]