Re: [syzbot] [bpf?] BUG: unable to handle kernel paging request in bpf_prog_ADDR (2)

[Stanislav Fomichev]

On 04/19, Alexei Starovoitov wrote:
> On Mon, Apr 8, 2024 at 8:53 PM syzbot
> <syzbot+838346b979830606c854@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    fe46a7dd189e Merge tag 'sound-6.9-rc1' of git://git.kernel..
> > git tree:       upstream
> > console+strace: https://syzkaller.appspot.com/x/log.txt?x=12596223180000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=4d90a36f0cab495a
> > dashboard link: https://syzkaller.appspot.com/bug?extid=838346b979830606c854
> > 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=134ecbb5180000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=141a8b3d180000
> >
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/f6c04726a2ae/disk-fe46a7dd.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/09c26ce901ea/vmlinux-fe46a7dd.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/134acf7f5322/bzImage-fe46a7dd.xz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+838346b979830606c854@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > BUG: unable to handle page fault for address: 0000001000000112
> > #PF: supervisor read access in kernel mode
> > #PF: error_code(0x0000) - not-present page
> > PGD 800000002e7b1067 P4D 800000002e7b1067 PUD 0
> > Oops: 0000 [#1] PREEMPT SMP KASAN PTI
> > CPU: 0 PID: 5060 Comm: syz-executor351 Not tainted 6.8.0-syzkaller-08951-gfe46a7dd189e #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
> > RIP: 0010:bpf_prog_a8e24a805b35c61b+0x19/0x1e
> > Code: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc f3 0f 1e fa 0f 1f 44 00 00 66 90 55 48 89 e5 f3 0f 1e fa 31 c0 48 8b 7f 18 <8b> 7f 00 c9 c3 cc cc cc cc cc cc 40 03 00 00 cc cc cc cc cc cc cc
> > RSP: 0018:ffffc90003b07b30 EFLAGS: 00010246
> > RAX: 0000000000000000 RBX: ffffc90000ace048 RCX: ffff88802aa89e00
> > RDX: 0000000000000000 RSI: ffffc90000ace048 RDI: 0000001000000112
> > RBP: ffffc90003b07b30 R08: ffffffff81bf633c R09: 1ffffffff2595ca0
> > R10: dffffc0000000000 R11: ffffffffa000095c R12: ffffc90000ace030
> > R13: ffff88802ac3ae28 R14: dffffc0000000000 R15: ffff88802ac3ae28
> > FS:  000055558f759380(0000) GS:ffff8880b9400000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 0000001000000112 CR3: 0000000077cfa000 CR4: 00000000003506f0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Call Trace:
> >  <TASK>
> >  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_prog_run_array_cg kernel/bpf/cgroup.c:51 [inline]
> >  __cgroup_bpf_run_filter_setsockopt+0x6fa/0x1040 kernel/bpf/cgroup.c:1830
> >  do_sock_setsockopt+0x6b4/0x720 net/socket.c:2293
> >  __sys_setsockopt+0x1ae/0x250 net/socket.c:2334
> >  __do_sys_setsockopt net/socket.c:2343 [inline]
> >  __se_sys_setsockopt net/socket.c:2340 [inline]
> >  __x64_sys_setsockopt+0xb5/0xd0 net/socket.c:2340
> >  do_syscall_64+0xfb/0x240
> >  entry_SYSCALL_64_after_hwframe+0x6d/0x75
> 
> This one looks interesting.
> But I cannot reproduce it.
> 
> Bjorn or Stan,
> 
> Could you take a look?
> 
> Probably a race in xdp dispatcher setup or the way cgroup-lsm
> logic is doing it.

Managed to repro it by hacking the C reproducer to attach bpf prog
to /sys/fs/cgroup instead of syzkallers custom path. Will try to
poke it a bit more..