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

[Dmitry Vyukov]

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%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?



> 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
> ==================================================================
>
>
> ---
> This report is generated by a bot. It may contain errors.
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> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx.
>
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