Re: [syzbot] WARNING: suspicious RCU usage in bpf_get_current_cgroup_id

[Yonghong Song <yhs@fb.com>]

On 7/24/21 12:47 AM, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    d6371c76e20d bpf: Fix OOB read when printing XDP link fdinfo
> git tree:       bpf
> console output: https://syzkaller.appspot.com/x/log.txt?x=146597f2300000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=6da37c7627210105
> dashboard link: https://syzkaller.appspot.com/bug?extid=7ee5c2c09c284495371f
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=126b7c40300000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1616cf6a300000
> 
> The issue was bisected to:
> 
> commit 79a7f8bdb159d9914b58740f3d31d602a6e4aca8
> Author: Alexei Starovoitov <ast@kernel.org>
> Date:   Fri May 14 00:36:03 2021 +0000
> 
>      bpf: Introduce bpf_sys_bpf() helper and program type.
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=14a73112300000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=16a73112300000
> console output: https://syzkaller.appspot.com/x/log.txt?x=12a73112300000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+7ee5c2c09c284495371f@syzkaller.appspotmail.com
> Fixes: 79a7f8bdb159 ("bpf: Introduce bpf_sys_bpf() helper and program type.")
> 
> =============================
> WARNING: suspicious RCU usage
> 5.14.0-rc1-syzkaller #0 Not tainted
> -----------------------------
> include/linux/cgroup.h:481 suspicious rcu_dereference_check() usage!

Looks like we may miss rcu_read_lock/rcu_read_unlock in this function,
static inline u32 bpf_prog_run_pin_on_cpu(const struct bpf_prog *prog,
                                           const void *ctx)
{
         u32 ret;

         migrate_disable();
         ret = __BPF_PROG_RUN(prog, ctx, bpf_dispatcher_nop_func);
         migrate_enable();
         return ret;
}

Will provide a fix soon.

> 
> other info that might help us debug this:
> 
> 
> rcu_scheduler_active = 2, debug_locks = 1
> no locks held by syz-executor499/8468.
> 
> stack backtrace:
> CPU: 1 PID: 8468 Comm: syz-executor499 Not tainted 5.14.0-rc1-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>   __dump_stack lib/dump_stack.c:88 [inline]
>   dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:105
>   task_css_set include/linux/cgroup.h:481 [inline]
>   task_dfl_cgroup include/linux/cgroup.h:550 [inline]
>   ____bpf_get_current_cgroup_id kernel/bpf/helpers.c:356 [inline]
>   bpf_get_current_cgroup_id+0x1ce/0x210 kernel/bpf/helpers.c:354
>   bpf_prog_08c4887f705f20b8+0x10/0x824
>   bpf_dispatcher_nop_func include/linux/bpf.h:687 [inline]
>   bpf_prog_run_pin_on_cpu include/linux/filter.h:624 [inline]
>   bpf_prog_test_run_syscall+0x2cf/0x5f0 net/bpf/test_run.c:954
>   bpf_prog_test_run kernel/bpf/syscall.c:3207 [inline]
>   __sys_bpf+0x1993/0x53b0 kernel/bpf/syscall.c:4487
>   __do_sys_bpf kernel/bpf/syscall.c:4573 [inline]
>   __se_sys_bpf kernel/bpf/syscall.c:4571 [inline]
>   __x64_sys_bpf+0x75/0xb0 kernel/bpf/syscall.c:4571
>   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>   do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>   entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x44d6a9
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 01 18 00 00 90 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:00007f32119dd318 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
> RAX: ffffffffffffffda RBX: 00000000004cb3e8 RCX: 000000000044d6a9
> RDX: 0000000000000048 RSI: 0000000020000500 RDI: 000000000000000a
> RBP: 00000000004cb3e0 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 656c6c616b7a7973
> R13: 00007ffeb7672e8f R14: 00007f32119dd400 R15: 0000000000022000
> 
> 
> ---
> 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:
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> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches
>