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From: Andrei Matei <andreimatei1@gmail.com>
Date: Thu, 21 Mar 2024 10:07:07 -0400
Message-ID: <CABWLsetWao1dd7mXJ2Gsq6JsPzkc=t3VRtAtreTSV03wGVUYCw@mail.gmail.com>
Subject: Re: stack access issue. Re: [syzbot] [bpf?] UBSAN:
 array-index-out-of-bounds in check_stack_range_initialized
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Andrii Nakryiko <andrii@kernel.org>, Alexei Starovoitov <ast@kernel.org>, bpf <bpf@vger.kernel.org>, 
	Daniel Borkmann <daniel@iogearbox.net>, Eddy Z <eddyz87@gmail.com>, Hao Luo <haoluo@google.com>, 
	John Fastabend <john.fastabend@gmail.com>, Jiri Olsa <jolsa@kernel.org>, 
	KP Singh <kpsingh@kernel.org>, LKML <linux-kernel@vger.kernel.org>, 
	Martin KaFai Lau <martin.lau@linux.dev>, Network Development <netdev@vger.kernel.org>, 
	Stanislav Fomichev <sdf@google.com>, Song Liu <song@kernel.org>, 
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>, Yonghong Song <yonghong.song@linux.dev>
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Thanks for the report! Will look in a bit.

On Thu, Mar 21, 2024 at 3:33=E2=80=AFAM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> Hi Andrei,
>
> looks like the refactoring of stack access introduced a bug.
> See the reproducer below.
> positive offsets are not caught by check_stack_access_within_bounds().
> So both slot and spi become negative and access
> stack[spi].slot_type[slot % BPF_REG_SIZE]
> returns garbage.
>
> On Tue, Mar 19, 2024 at 11:12=E2=80=AFAM syzbot
> <syzbot+33f4297b5f927648741a@syzkaller.appspotmail.com> wrote:
> >
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    0740b6427e90 Merge branch 'bpf-arena-followups'
> > git tree:       bpf
> > console+strace: https://syzkaller.appspot.com/x/log.txt?x=3D12fed769180=
000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=3D6fb1be60a19=
3d440
> > dashboard link: https://syzkaller.appspot.com/bug?extid=3D33f4297b5f927=
648741a
> > compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for D=
ebian) 2.40
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=3D1763a4791=
80000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=3D15c38711180=
000
> >
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/c9e6e9f97566/d=
isk-0740b642.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/78476a588b62/vmli=
nux-0740b642.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/50cd6fab9ead=
/bzImage-0740b642.xz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the co=
mmit:
> > Reported-by: syzbot+33f4297b5f927648741a@syzkaller.appspotmail.com
> >
> > ------------[ cut here ]------------
> > UBSAN: array-index-out-of-bounds in kernel/bpf/verifier.c:7190:12
> > index -1 is out of range for type 'u8[8]' (aka 'unsigned char[8]')
> > CPU: 0 PID: 5071 Comm: syz-executor474 Not tainted 6.8.0-syzkaller-0522=
6-g0740b6427e90 #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS=
 Google 02/29/2024
> > Call Trace:
> >  <TASK>
> >  __dump_stack lib/dump_stack.c:88 [inline]
> >  dump_stack_lvl+0x1e7/0x2e0 lib/dump_stack.c:106
> >  ubsan_epilogue lib/ubsan.c:217 [inline]
> >  __ubsan_handle_out_of_bounds+0x121/0x150 lib/ubsan.c:415
> >  check_stack_range_initialized+0x1668/0x19a0 kernel/bpf/verifier.c:7190
> >  check_helper_mem_access+0x2eb/0xfa0 kernel/bpf/verifier.c:7294
> >  check_helper_call+0x263c/0x7220 kernel/bpf/verifier.c:10252
> >  do_check+0x9e29/0x10530 kernel/bpf/verifier.c:17801
> >  do_check_common+0x14bd/0x1dd0 kernel/bpf/verifier.c:20500
> >  do_check_main kernel/bpf/verifier.c:20591 [inline]
> >  bpf_check+0x136ab/0x19010 kernel/bpf/verifier.c:21261
> >  bpf_prog_load+0x1667/0x20f0 kernel/bpf/syscall.c:2895
> >  __sys_bpf+0x4ee/0x810 kernel/bpf/syscall.c:5631
> >  __do_sys_bpf kernel/bpf/syscall.c:5738 [inline]
> >  __se_sys_bpf kernel/bpf/syscall.c:5736 [inline]
> >  __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5736
> >  do_syscall_64+0xfb/0x240
> >  entry_SYSCALL_64_after_hwframe+0x6d/0x75
> > RIP: 0033:0x7f8416194629
> > Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 00 00 48 89 f8 48 89=
 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 =
ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
> > RSP: 002b:00007ffdc6f0fdb8 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
> > RAX: ffffffffffffffda RBX: 00007ffdc6f0ff88 RCX: 00007f8416194629
> > RDX: 0000000000000090 RSI: 00000000200000c0 RDI: 0000000000000005
> > RBP: 00007f8416207610 R08: 0000000000000000 R09: 00007ffdc6f0ff88
> > R10: 00000000fffffff8 R11: 0000000000000246 R12: 0000000000000001
> > R13: 00007ffdc6f0ff78 R14: 0000000000000001 R15: 0000000000000001
> >  </TASK>
> > ---[ end trace ]---
> >
> >
> > ---
> > 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 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