linux-kernel - Re: [syzbot] [mm?] KMSAN: kernel-infoleak in bpf_probe_write

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Message-ID: <CAADnVQ+E=j1Z4MOuk2f-U33oqvUmmrRcvWvsDrmLXvD8FhUmsQ@mail.gmail.com>
Date: Mon, 15 Apr 2024 14:06:39 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: syzbot <syzbot+79102ed905e5b2dc0fc3@...kaller.appspotmail.com>, 
	LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>, 
	syzkaller-bugs <syzkaller-bugs@...glegroups.com>, bpf <bpf@...r.kernel.org>
Subject: Re: [syzbot] [mm?] KMSAN: kernel-infoleak in bpf_probe_write_user

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".

On Mon, Apr 15, 2024 at 1:18 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> (cc bpf@)
>
> On Fri, 12 Apr 2024 19:27:25 -0700 syzbot <syzbot+79102ed905e5b2dc0fc3@...kaller.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=16509ba1180000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=13e7da432565d94c
> > dashboard link: https://syzkaller.appspot.com/bug?extid=79102ed905e5b2dc0fc3
> > 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=10a4af9d180000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12980f9d180000
> >
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/901017b36ccc/disk-fec50db7.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/16bfcf5618d3/vmlinux-fec50db7.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/dc9c5a1e7d02/bzImage-fec50db7.xz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+79102ed905e5b2dc0fc3@...kaller.appspotmail.com
> >
> > =====================================================
> > 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/maccess.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, BIOS Google 03/27/2024
> > =====================================================
> >
> >
> > ---
> > 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@...glegroups.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 testing.
> >
> > 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
>