linux-kernel - Re: [PATCH] kernel: kallsyms: parameters checking, for EXPORT_SYMBOL

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Message-ID: <87ppy14w3u.fsf@rustcorp.com.au>
Date:	Thu, 11 Apr 2013 12:22:37 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Chen Gang <gang.chen@...anux.com>
Cc:	Stephen Boyd <sboyd@...eaurora.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kernel: kallsyms: parameters checking, for EXPORT_SYMBOL_GPL functions

Chen Gang <gang.chen@...anux.com> writes:
> On 2013年04月10日 14:57, Rusty Russell wrote:
>> Chen Gang <gang.chen@...anux.com> writes:
>>> >   for EXPORT_SYMBOL_GPL functions, necessary to check their parameters.
>>> >
>>> > Signed-off-by: Chen Gang <gang.chen@...anux.com>
>> Why?
>> 
>> If someone misuses these functions, they crash and thus indicate that
>> the caller shouldn't do that.
>> 
>
>   for me, I think:
>
>     if it is used by self (such as static functions):
>       I prefer to crash immediatly.
>       it will help us to find issue, quickly.
>
>     if it can be used by others (such as EXPORT_SYMBOL_GPL):
>       I prefer to return fail and tell caller that parameter is invalid.
>       it is more polite to callers, and still indicate it may be an issue.
>
>   :-)

I disagree.  Calling with invalid parameters is a bug.  You've just
covered up some cases of invalid use and made it less likely to be
found.  Because the caller won't notice they screwed up.

We could sprinkle WARN_ON() everywhere, but I prefer the crash.  Even
harder to ignore.

There's no limit to how many of these checks we could put in, and we can
*never* take them out.  I don't want to code that way.

>> Or is someone already doing this?
>> 
>
>   really has:
>
>     kernel: __wake_up_sync_key in kernel/sched/core.c.
>     lib: *printf.
>     mm:  kfree.

No, I mean "is someone calling these functions with NULL".

Cheers,
Rusty.
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