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Date:   Thu, 23 Sep 2021 19:23:12 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Chen Jun <chenjun102@huawei.com>
Cc:     <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
        <feng.tang@intel.com>, <mhocko@suse.com>, <rui.xiang@huawei.com>
Subject: Re: [PATCH v3 1/1] mm: Fix the uninitialized use in
 overcommit_policy_handler
Message-Id: <20210923192312.53dbe65db0375038c99defaa@linux-foundation.org>
In-Reply-To: <20210923020524.13289-1-chenjun102@huawei.com>
References: <20210923020524.13289-1-chenjun102@huawei.com>
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On Thu, 23 Sep 2021 02:05:24 +0000 Chen Jun <chenjun102@huawei.com> wrote:

> An unexpected value of /proc/sys/vm/overcommit_memory we will get,
> after running the following program.
> 
> int main()
> {
>     int fd = open("/proc/sys/vm/overcommit_memory", O_RDWR)
>     write(fd, "1", 1);
>     write(fd, "2", 1);
>     close(fd);
> }
> 
> write(fd, "2", 1) will pass *ppos = 1 to proc_dointvec_minmax.
> proc_dointvec_minmax will return 0 without setting new_policy.
> 
> t.data = &new_policy;
> ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos)
>       -->do_proc_dointvec
>          -->__do_proc_dointvec
>               if (write) {
>                 if (proc_first_pos_non_zero_ignore(ppos, table))
>                   goto out;
> 
> sysctl_overcommit_memory = new_policy;
> 
> so sysctl_overcommit_memory will be set to an uninitialized value.
> 
> Check whether new_policy has been changed by proc_dointvec_minmax.
> 

Thanks.  I added a cc:stable to this, so the fix will be backported
into earlier kernels.