Re: [PATCH] kernel: kallsyms: parameters checking, for EXPORT_SYMBOL_GPL functions

Rusty Russell
2013-04-11T04:01:01Z

Chen Gang <gang.chen@asianux.com> writes:
> On 2013年04月10日 14:57, Rusty Russell wrote:
>> Chen Gang <gang.chen@asianux.com> writes:
>>> > for EXPORT_SYMBOL_GPL functions, necessary to check their parameters.
>>> >
>>> > Signed-off-by: Chen Gang <gang.chen@asianux.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.