Re: [PATCH -next] cgroup/cpuset: fix null-ptr-deref in rebuild_sched_domains_cpuslocked

[Waiman Long <llong@redhat.com>]

On 2/24/26 8:15 PM, Chen Ridong wrote:
> From: Chen Ridong <chenridong@huawei.com>
>
> A null-pointer-dereference bug was reported by syzbot:
>
> Oops: general protection fault, probably for address 0xdffffc0000000000:
> KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
> 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 kernel/cgroup/cpuset.c:967
> 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
> 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
>
> The issue occurs when generate_sched_domains() returns ndoms = 1 and
> doms = NULL due to a kmalloc failure. This leads to a null-pointer
> dereference when accessing doms in rebuild_sched_domains_locked().
>
> Fix this by adding a NULL check for doms before accessing it.
>
> Fixes: 6ee43047e8ad ("cpuset: Remove unnecessary checks in rebuild_sched_domains_locked")
> Reported-by: syzbot+460792609a79c085f79f@syzkaller.appspotmail.com
> Signed-off-by: Chen Ridong <chenridong@huawei.com>
> ---
>   kernel/cgroup/cpuset.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 9faf34377a88..8ebf2ab8f0df 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -962,7 +962,8 @@ void rebuild_sched_domains_locked(void)
>   	* prevent the panic.
>   	*/
>   	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;
>   	}
>   

I would prefer putting the doms check in the for loop without the line 
wrap, but that will work too.

Acked-by: Waiman Long <longman@redhat.com>