Re: [syzbot] [cgroups?] general protection fault in rebuild_sched_domains_locked

[Waiman Long <llong@redhat.com>]

On 2/23/26 11:03 PM, Chen Ridong wrote:
>
> On 2026/2/16 13:57, Waiman Long wrote:
>> On 2/15/26 4:05 PM, syzbot wrote:
>>> Hello,
>>>
>>> syzbot found the following issue on:
>>>
>>> HEAD commit:    37a93dd5c49b Merge tag 'net-next-7.0' of git://git.kernel...
>>> git tree:       upstream
>>> console output: https://syzkaller.appspot.com/x/log.txt?x=1649d073980000
>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=a512b4a06724b76a
>>> dashboard link: https://syzkaller.appspot.com/bug?extid=460792609a79c085f79f
>>> compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for
>>> Debian) 2.44
>>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=152086e6580000
>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=139c2eef980000
>>>
>>> Downloadable assets:
>>> disk image:
>>> https://storage.googleapis.com/syzbot-assets/0dedaafff2ad/disk-37a93dd5.raw.xz
>>> vmlinux:
>>> https://storage.googleapis.com/syzbot-assets/aa7fae081497/vmlinux-37a93dd5.xz
>>> kernel image:
>>> https://storage.googleapis.com/syzbot-assets/9096b39b53e1/bzImage-37a93dd5.xz
>>>
>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>>> Reported-by: syzbot+460792609a79c085f79f@syzkaller.appspotmail.com
>>>
>>> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
>>> R13: 00007fe00de15fac R14: 00007fe00de15fa0 R15: 00007fe00de15fa0
>>>    </TASK>
>>> Oops: general protection fault, probably for non-canonical address
>>> 0xdffffc0000000000: 0000 [#1] SMP KASAN PTI
>>> KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
>>> CPU: 1 UID: 0 PID: 5994 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google
>>> 01/24/2026
>>> RIP: 0010:bitmap_subset include/linux/bitmap.h:433 [inline]
>>> RIP: 0010:cpumask_subset include/linux/cpumask.h:836 [inline]
>>> RIP: 0010:rebuild_sched_domains_locked+0x2aa/0x980 kernel/cgroup/cpuset.c:967
>>> Code: 7d 05 00 41 83 c4 01 89 de 48 83 c5 08 44 89 e7 e8 fb 76 05 00 41 39 dc
>>> 0f 8d 4c 04 00 00 e8 fd 7c 05 00 48 89 e8 48 c1 e8 03 <42> 80 3c 30 00 0f 85
>>> 1d 06 00 00 48 8b 04 24 48 23 45 00 31 ff 44
>>> RSP: 0018:ffffc90003ecfbc0 EFLAGS: 00010246
>>> RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000020
>>> RDX: ffff888028de0000 RSI: ffffffff8200f003 RDI: ffffffff8df14f28
>>> RBP: 0000000000000000 R08: 0000000000000cc0 R09: 00000000ffffffff
>>> R10: ffffffff8e7d95b3 R11: 0000000000000001 R12: 0000000000000000
>>> R13: 00000000000f4240 R14: dffffc0000000000 R15: 0000000000000000
>>> FS:  000055555c694500(0000) GS:ffff8881246a5000(0000) knlGS:0000000000000000
>>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> CR2: 0000001b2f463fff CR3: 000000003704c000 CR4: 00000000003526f0
>>> Call Trace:
>>>    <TASK>
>>>    rebuild_sched_domains_cpuslocked kernel/cgroup/cpuset.c:983 [inline]
>>>    rebuild_sched_domains+0x21/0x40 kernel/cgroup/cpuset.c:990
>>>    sched_rt_handler+0xb5/0xe0 kernel/sched/rt.c:2911
>>>    proc_sys_call_handler+0x47f/0x5a0 fs/proc/proc_sysctl.c:600
>>>    new_sync_write fs/read_write.c:595 [inline]
>>>    vfs_write+0x6ac/0x1070 fs/read_write.c:688
>>>    ksys_write+0x12a/0x250 fs/read_write.c:740
>>>    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>>>    do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
>>>    entry_SYSCALL_64_after_hwframe+0x77/0x7f
>>> RIP: 0033:0x7fe00db9bf79
>>> Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 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 e8 ff ff ff f7 d8 64 89 01 48
>>> RSP: 002b:00007fff27bcda88 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
>>> RAX: ffffffffffffffda RBX: 00007fe00de15fa0 RCX: 00007fe00db9bf79
>>> RDX: 00000000000000f6 RSI: 0000200000000000 RDI: 0000000000000003
>>> RBP: 00007fff27bcdaf0 R08: 0000000000000000 R09: 0000000000000000
>>> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
>>> R13: 00007fe00de15fac R14: 00007fe00de15fa0 R15: 00007fe00de15fa0
>>>    </TASK>
>>> Modules linked in:
>>> ---[ end trace 0000000000000000 ]---
>>> RIP: 0010:bitmap_subset include/linux/bitmap.h:433 [inline]
>>> RIP: 0010:cpumask_subset include/linux/cpumask.h:836 [inline]
>>> RIP: 0010:rebuild_sched_domains_locked+0x2aa/0x980 kernel/cgroup/cpuset.c:967
>>> Code: 7d 05 00 41 83 c4 01 89 de 48 83 c5 08 44 89 e7 e8 fb 76 05 00 41 39 dc
>>> 0f 8d 4c 04 00 00 e8 fd 7c 05 00 48 89 e8 48 c1 e8 03 <42> 80 3c 30 00 0f 85
>>> 1d 06 00 00 48 8b 04 24 48 23 45 00 31 ff 44
>>> RSP: 0018:ffffc90003ecfbc0 EFLAGS: 00010246
>>> RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000020
>>> RDX: ffff888028de0000 RSI: ffffffff8200f003 RDI: ffffffff8df14f28
>>> RBP: 0000000000000000 R08: 0000000000000cc0 R09: 00000000ffffffff
>>> R10: ffffffff8e7d95b3 R11: 0000000000000001 R12: 0000000000000000
>>> R13: 00000000000f4240 R14: dffffc0000000000 R15: 0000000000000000
>>> FS:  000055555c694500(0000) GS:ffff8881246a5000(0000) knlGS:0000000000000000
>>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> CR2: 0000001b2f463fff CR3: 000000003704c000 CR4: 00000000003526f0
>>> ----------------
>>> Code disassembly (best guess), 1 bytes skipped:
>>>      0:    05 00 41 83 c4           add    $0xc4834100,%eax
>>>      5:    01 89 de 48 83 c5        add    %ecx,-0x3a7cb722(%rcx)
>>>      b:    08 44 89 e7              or     %al,-0x19(%rcx,%rcx,4)
>>>      f:    e8 fb 76 05 00           call   0x5770f
>>>     14:    41 39 dc                 cmp    %ebx,%r12d
>>>     17:    0f 8d 4c 04 00 00        jge    0x469
>>>     1d:    e8 fd 7c 05 00           call   0x57d1f
>>>     22:    48 89 e8                 mov    %rbp,%rax
>>>     25:    48 c1 e8 03              shr    $0x3,%rax
>>> * 29:    42 80 3c 30 00           cmpb   $0x0,(%rax,%r14,1) <-- trapping
>>> instruction
>>>     2e:    0f 85 1d 06 00 00        jne    0x651
>>>     34:    48 8b 04 24              mov    (%rsp),%rax
>>>     38:    48 23 45 00              and    0x0(%rbp),%rax
>>>     3c:    31 ff                    xor    %edi,%edi
>>>     3e:    44                       rex.R
>> The cpuset.c:967 is:
>>
>>      966         for (i = 0; i < ndoms; ++i) {
>>      967                 if (WARN_ON_ONCE(!cpumask_subset(doms[i],
>> cpu_active_mask)))
>>      968                         return;
>>
>> The oops was caused by accessing doms[i] which was kmalloc'ed in
>> generate_sched_domains() by calling alloc_sched_domains() in
>> kernel/sched/topology.c. Looking at the console log just before the oops, I saw
>>
>> [  124.398850][ T5994] FAULT_INJECTION: forcing a failure.
>> [  124.398850][ T5994] name failslab, interval 1, probability 0, space 0, times 1
>> [  124.434865][ T5994] CPU: 1 UID: 0 PID: 5994 Comm: syz.0.17 Not tainted
>> syzkaller #0 PREEMPT(full)
>> [  124.434909][ T5994] Hardware name: Google Google Compute Engine/Google
>> Compute Engine, BIOS Google 01/24/2026
>> [  124.434936][ T5994] Call Trace:
>> [  124.434947][ T5994]  <TASK>
>> [  124.434959][ T5994]  dump_stack_lvl+0x100/0x190
>> [  124.435026][ T5994]  should_fail_ex.cold+0x5/0xa
>> [  124.435062][ T5994]  ? rebuild_sched_domains_locked+0x51/0x980
>> [  124.435113][ T5994]  should_failslab+0xc2/0x120
>> [  124.435153][ T5994]  __kmalloc_noprof+0xe0/0x850
>> [  124.435195][ T5994]  rebuild_sched_domains_locked+0x51/0x980
>> [  124.435266][ T5994]  rebuild_sched_domains+0x21/0x40
>> [  124.435314][ T5994]  sched_rt_handler+0xb5/0xe0
>> [  124.435359][ T5994]  proc_sys_call_handler+0x47f/0x5a0
>> [  124.435413][ T5994]  ? __pfx_proc_sys_call_handler+0x10/0x10
>> [  124.435475][ T5994]  vfs_write+0x6ac/0x1070
>> [  124.435511][ T5994]  ? __pfx_proc_sys_write+0x10/0x10
>> [  124.435562][ T5994]  ? __pfx_vfs_write+0x10/0x10
>> [  124.435597][ T5994]  ? __pfx_do_sys_openat2+0x10/0x10
>> [  124.435664][ T5994]  ksys_write+0x12a/0x250
>> [  124.435696][ T5994]  ? __pfx_ksys_write+0x10/0x10
>> [  124.435730][ T5994]  ? do_user_addr_fault+0x8d6/0x12f0
>> [  124.435787][ T5994]  do_syscall_64+0x106/0xf80
>> [  124.435834][ T5994]  ? clear_bhb_loop+0x40/0x90
>> [  124.435875][ T5994]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>>
>> So it looks like the oops may be expected. It may not be a bug in the cpuset
>> AFAICS.
>>
> Hi Longman,
>
> Thank you for looking into this issue.
>
> Since partition_sched_domains_locked can handle the situation where 'doms' is
> NULL, I think we should make it robust and fix it.
>
> The fix can be implemented as follows:
>
> In cpuset.c at line 964:
>
>          for (i = 0; i < ndoms; ++i) {
> -               if (WARN_ON_ONCE(!cpumask_subset(doms[i], cpu_active_mask)))
> +               if (doms && WARN_ON_ONCE(!cpumask_subset(doms[i],
> +                                         cpu_active_mask)))
>                          return;
>          }
>
The problem is that doms is not NULL. It is 0xdffffc0000000000 as shown 
in the dmesg log. So the null check here won't do any good in this 
particular case. In fact, there is already a null check right after 
alloc_sched_domains() above.

Cheers, Longman