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From: Alexander Potapenko <glider@google.com>
Date: Tue, 16 Apr 2024 10:52:12 +0200
Message-ID: <CAG_fn=Uxaq1juuq-3cA1qQu6gB7ZB=LpyxBEdKf7DpYfAo3zmg@mail.gmail.com>
Subject: Re: [syzbot] [mm?] KMSAN: kernel-infoleak in bpf_probe_write_user
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, 
	syzbot <syzbot+79102ed905e5b2dc0fc3@syzkaller.appspotmail.com>, 
	LKML <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>, 
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>, bpf <bpf@vger.kernel.org>
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On Mon, Apr 15, 2024 at 11:06=E2=80=AFPM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> Hi,
>
> syzbot folks, please disable such "bug" reporting.
> The whole point of bpf is to pass such info to userspace.
> probe_write_user, various ring buffers, bpf_*_printk-s, bpf maps
> all serve this purpose of "infoleak".
>

Hi Alexei,

From KMSAN's perspective it is fine to pass information to the
userspace, unless it is marked as uninitialized.
It could be that we are missing some initialization in kernel/bpf/core.c th=
ough.
Do you know which part of the code is supposed to initialize the stack
in PROG_NAME?

> On Mon, Apr 15, 2024 at 1:18=E2=80=AFPM Andrew Morton <akpm@linux-foundat=
ion.org> wrote:
> >
> > (cc bpf@)
> >
> > On Fri, 12 Apr 2024 19:27:25 -0700 syzbot <syzbot+79102ed905e5b2dc0fc3@=
syzkaller.appspotmail.com> wrote:
> >
> > > Hello,
> > >
> > > syzbot found the following issue on:
> > >
> > > HEAD commit:    fec50db7033e Linux 6.9-rc3
> > > git tree:       upstream
> > > console+strace: https://syzkaller.appspot.com/x/log.txt?x=3D16509ba11=
80000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=3D13e7da432=
565d94c
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=3D79102ed905e=
5b2dc0fc3
> > > compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for=
 Debian) 2.40
> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=3D10a4af9=
d180000
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=3D12980f9d1=
80000
> > >
> > > Downloadable assets:
> > > disk image: https://storage.googleapis.com/syzbot-assets/901017b36ccc=
/disk-fec50db7.raw.xz
> > > vmlinux: https://storage.googleapis.com/syzbot-assets/16bfcf5618d3/vm=
linux-fec50db7.xz
> > > kernel image: https://storage.googleapis.com/syzbot-assets/dc9c5a1e7d=
02/bzImage-fec50db7.xz
> > >
> > > IMPORTANT: if you fix the issue, please add the following tag to the =
commit:
> > > Reported-by: syzbot+79102ed905e5b2dc0fc3@syzkaller.appspotmail.com
> > >
> > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D
> > > BUG: KMSAN: kernel-infoleak in instrument_copy_to_user include/linux/=
instrumented.h:114 [inline]
> > > BUG: KMSAN: kernel-infoleak in __copy_to_user_inatomic include/linux/=
uaccess.h:125 [inline]
> > > BUG: KMSAN: kernel-infoleak in copy_to_user_nofault+0x129/0x1f0 mm/ma=
ccess.c:149
> > >  instrument_copy_to_user include/linux/instrumented.h:114 [inline]
> > >  __copy_to_user_inatomic include/linux/uaccess.h:125 [inline]
> > >  copy_to_user_nofault+0x129/0x1f0 mm/maccess.c:149
> > >  ____bpf_probe_write_user kernel/trace/bpf_trace.c:349 [inline]
> > >  bpf_probe_write_user+0x104/0x180 kernel/trace/bpf_trace.c:327
> > >  ___bpf_prog_run+0x13fe/0xe0f0 kernel/bpf/core.c:1997
> > >  __bpf_prog_run64+0xb5/0xe0 kernel/bpf/core.c:2236
> > >  bpf_dispatcher_nop_func include/linux/bpf.h:1234 [inline]
> > >  __bpf_prog_run include/linux/filter.h:657 [inline]
> > >  bpf_prog_run include/linux/filter.h:664 [inline]
> > >  __bpf_trace_run kernel/trace/bpf_trace.c:2381 [inline]
> > >  bpf_trace_run2+0x116/0x300 kernel/trace/bpf_trace.c:2420
> > >  __bpf_trace_kfree+0x29/0x40 include/trace/events/kmem.h:94
> > >  trace_kfree include/trace/events/kmem.h:94 [inline]
> > >  kfree+0x6a5/0xa30 mm/slub.c:4377
> > >  vfs_writev+0x12bf/0x1450 fs/read_write.c:978
> > >  do_writev+0x251/0x5c0 fs/read_write.c:1018
> > >  __do_sys_writev fs/read_write.c:1091 [inline]
> > >  __se_sys_writev fs/read_write.c:1088 [inline]
> > >  __x64_sys_writev+0x98/0xe0 fs/read_write.c:1088
> > >  do_syscall_64+0xd5/0x1f0
> > >  entry_SYSCALL_64_after_hwframe+0x72/0x7a
> > >
> > > Local variable stack created at:
> > >  __bpf_prog_run64+0x45/0xe0 kernel/bpf/core.c:2236
> > >  bpf_dispatcher_nop_func include/linux/bpf.h:1234 [inline]
> > >  __bpf_prog_run include/linux/filter.h:657 [inline]
> > >  bpf_prog_run include/linux/filter.h:664 [inline]
> > >  __bpf_trace_run kernel/trace/bpf_trace.c:2381 [inline]
> > >  bpf_trace_run2+0x116/0x300 kernel/trace/bpf_trace.c:2420
> > >
> > > Bytes 0-7 of 8 are uninitialized
> > > Memory access of size 8 starts at ffff888121ec7ae8
> > > Data copied to user address 00000000ffffffff
> > >
> > > CPU: 1 PID: 4779 Comm: dhcpcd Not tainted 6.9.0-rc3-syzkaller #0
> > > Hardware name: Google Google Compute Engine/Google Compute Engine, BI=
OS Google 03/27/2024
> > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D
> > >
> > >
> > > ---
> > > 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.
> > >
> > > If the report is already addressed, let syzbot know by replying with:
> > > #syz fix: exact-commit-title
> > >
> > > If you want syzbot to run the reproducer, reply with:
> > > #syz test: git://repo/address.git branch-or-commit-hash
> > > If you attach or paste a git patch, syzbot will apply it before testi=
ng.
> > >
> > > If you want to overwrite report's subsystems, reply with:
> > > #syz set subsystems: new-subsystem
> > > (See the list of subsystem names on the web dashboard)
> > >
> > > If the report is a duplicate of another one, reply with:
> > > #syz dup: exact-subject-of-another-report
> > >
> > > If you want to undo deduplication, reply with:
> > > #syz undup
> >
>
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mail.gmail.com.


--
Alexander Potapenko
Software Engineer

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