linux-kernel - Re: [PATCH v3] proc_sysctl: fix oops caused by incorrect command parameters.

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Date:   Mon, 11 Jan 2021 22:28:45 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Xiaoming Ni <nixiaoming@...wei.com>
Cc:     <linux-kernel@...r.kernel.org>, <mcgrof@...nel.org>,
        <keescook@...omium.org>, <yzaikin@...gle.com>,
        <adobriyan@...il.com>, <linux-fsdevel@...r.kernel.org>,
        <vbabka@...e.cz>, <mhocko@...e.com>, <andy.shevchenko@...il.com>,
        <wangle6@...wei.com>
Subject: Re: [PATCH v3] proc_sysctl: fix oops caused by incorrect command
 parameters.

On Tue, 12 Jan 2021 14:24:05 +0800 Xiaoming Ni <nixiaoming@...wei.com> wrote:

> On 2021/1/12 12:33, Andrew Morton wrote:
> > On Tue, 12 Jan 2021 11:31:55 +0800 Xiaoming Ni <nixiaoming@...wei.com> wrote:
> > 
> >> The process_sysctl_arg() does not check whether val is empty before
> >>   invoking strlen(val). If the command line parameter () is incorrectly
> >>   configured and val is empty, oops is triggered.
> >>
> >> --- a/fs/proc/proc_sysctl.c
> >> +++ b/fs/proc/proc_sysctl.c
> >> @@ -1770,6 +1770,9 @@ static int process_sysctl_arg(char *param, char *val,
> >>   			return 0;
> >>   	}
> >>   
> >> +	if (!val)
> >> +		return -EINVAL;
> >> +
> > 
> > I think v2 (return 0) was preferable.  Because all the other error-out
> > cases in process_sysctl_arg() also do a `return 0'.
> 
> https://lore.kernel.org/lkml/bc098af4-c0cd-212e-d09d-46d617d0acab@huawei.com/
> 
> patch4:
>      +++ b/fs/proc/proc_sysctl.c
>      @@ -1757,6 +1757,9 @@ static int process_sysctl_arg(char *param, 
> char *val,
>              loff_t pos = 0;
>              ssize_t wret;
> 
>      +       if (!val)
>      +               return 0;
>      +
>              if (strncmp(param, "sysctl", sizeof("sysctl") - 1) == 0) {
>                      param += sizeof("sysctl") - 1;
> 
> Is this the version you're talking about?

yes, but as a separate patch.  The bugfix comes first.

> > 
> > If we're going to do a separate "patch: make process_sysctl_arg()
> > return an errno instead of 0" then fine, we can discuss that.  But it's
> > conceptually a different work from fixing this situation.
> > .
> > 
> However, are the logs generated by process_sysctl_arg() clearer and more 
> accurate than parse_args()? Should the logs generated by 
> process_sysctl_arg() be deleted?

I think the individual logs are very useful and should be retained.