linux-kernel - Re: [PATCH] sched/numa: Fix the potential null pointer dereference in task_numa

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Message-ID: <20241025073648.GA14555@noisy.programming.kicks-ass.net>
Date: Fri, 25 Oct 2024 09:36:48 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Shawn Wang <shawnwang@...ux.alibaba.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Liam.Howlett@...cle.com, akpm@...ux-foundation.org,
	baolin.wang@...ux.alibaba.com, mingo@...hat.com,
	juri.lelli@...hat.com, vincent.guittot@...aro.org,
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
	mgorman@...e.de, vschneid@...hat.com
Subject: Re: [PATCH] sched/numa: Fix the potential null pointer dereference
 in task_numa_work()

On Fri, Oct 25, 2024 at 10:22:08AM +0800, Shawn Wang wrote:
> When running stress-ng-vm-segv test, we found a null pointer dereference
> error in task_numa_work(). Here is the backtrace:
> 
>   [323676.066985] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000020
>   ......
>   [323676.067108] CPU: 35 PID: 2694524 Comm: stress-ng-vm-se
>   ......
>   [323676.067113] pstate: 23401009 (nzCv daif +PAN -UAO +TCO +DIT +SSBS BTYPE=--)
>   [323676.067115] pc : vma_migratable+0x1c/0xd0
>   [323676.067122] lr : task_numa_work+0x1ec/0x4e0
>   [323676.067127] sp : ffff8000ada73d20
>   [323676.067128] x29: ffff8000ada73d20 x28: 0000000000000000 x27: 000000003e89f010
>   [323676.067130] x26: 0000000000080000 x25: ffff800081b5c0d8 x24: ffff800081b27000
>   [323676.067133] x23: 0000000000010000 x22: 0000000104d18cc0 x21: ffff0009f7158000
>   [323676.067135] x20: 0000000000000000 x19: 0000000000000000 x18: ffff8000ada73db8
>   [323676.067138] x17: 0001400000000000 x16: ffff800080df40b0 x15: 0000000000000035
>   [323676.067140] x14: ffff8000ada73cc8 x13: 1fffe0017cc72001 x12: ffff8000ada73cc8
>   [323676.067142] x11: ffff80008001160c x10: ffff000be639000c x9 : ffff8000800f4ba4
>   [323676.067145] x8 : ffff000810375000 x7 : ffff8000ada73974 x6 : 0000000000000001
>   [323676.067147] x5 : 0068000b33e26707 x4 : 0000000000000001 x3 : ffff0009f7158000
>   [323676.067149] x2 : 0000000000000041 x1 : 0000000000004400 x0 : 0000000000000000
>   [323676.067152] Call trace:
>   [323676.067153]  vma_migratable+0x1c/0xd0
>   [323676.067155]  task_numa_work+0x1ec/0x4e0
>   [323676.067157]  task_work_run+0x78/0xd8
>   [323676.067161]  do_notify_resume+0x1ec/0x290
>   [323676.067163]  el0_svc+0x150/0x160
>   [323676.067167]  el0t_64_sync_handler+0xf8/0x128
>   [323676.067170]  el0t_64_sync+0x17c/0x180
>   [323676.067173] Code: d2888001 910003fd f9000bf3 aa0003f3 (f9401000)
>   [323676.067177] SMP: stopping secondary CPUs
>   [323676.070184] Starting crashdump kernel...
> 
> stress-ng-vm-segv in stress-ng is used to stress test the SIGSEGV error
> handling function of the system, which tries to cause a SIGSEGV error on
> return from unmapping the whole address space of the child process.
> 
> Normally this program will not cause kernel crashes. But before the
> munmap system call returns to user mode, a potential task_numa_work()
> for numa balancing could be added and executed. In this scenario, since the
> child process has no vma after munmap, the vma_next() in task_numa_work()
> will return a null pointer even if the vma iterator restarts from 0.
> 
> Recheck the vma pointer before dereferencing it in task_numa_work().
> 
> Fixes: 214dbc428137 ("sched: convert to vma iterator")
> Cc: stable@...r.kernel.org # v6.2+

Thanks